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Brodie Reid
Lead author
Dr Brodie Reid teaches secondary science and Years 11 and 12 ATAR Chemistry at a Perth school. He also has many years of experience teaching at the tertiary level and is an author of more than 10 academic publications. He has presented his research internationally, winning several awards along the way.
Gemma Dale
Dr Gemma Dale is a nationally certified lead teacher, working as a senior biology teacher at a Brisbane school. With more than 17 years’ experience teaching senior sciences in the UK and Australia, she also has a tertiary background in ecology and a Master of Science in Biodiversity and Conservation. She has also completed an education doctorate (EdD), specialising in scientific literacy.
The publisher thanks XX for reviewing and contributing to this resource.
6.1
6.2
6.3
7.1
7.3
7.4
7.5
Glossary
Definitions of key terms are provided next to where the key terms first appear in the chapter.
Students are encouraged to conduct research online to find and interpret information.
These provide quick checks for recalling facts and understanding content. Cognitive verbs appear in bold. These questions can be completed in the Interactive Textbook or downloaded as Word documents.
These are descriptions of what the student will learn throughout the section.
These are short facts that contain interesting information.
These are recent developments in the particular area of science being covered. They may also show how ideas in science have changed over the years through human discovery and inventions.
Question sets at the ends of sections are categorised under five headings: Remembering, Understanding, Applying, Analysing and Evaluating. Cognitive verbs appear in bold. These questions can be completed in the Interactive Textbook or downloaded as Word documents.
Classroom activities help explore concepts that are currently being covered.
Visible-thinking-style classroom activities help consolidate the concepts currently being covered.
Practical
These activities focus on developing science inquiry skills, including using laboratory equipment. These activities are also available as Word document downloads in the Interactive Textbook.
Chapter checklist
Success criteria Linked questions
2.1 I can recall the components that make up the structure of DNA and RNA molecules. 6, 13
2.1 I can describe the relationship between genes, DNA and chromosomes. 1
2.1 I can describe the steps in which DNA is used to synthesise proteins.7, 18
2.2 I can recall the steps involved in DNA replication. 3, 4, 15
2.2 I can describe the stages of cell division in mitosis. 17
2.2 I can describe the stages of cell division in meiosis. 17
2.2 I can use a karyotype to determine information about an individual.10
2.3 I can define the terms ‘homozygous’, ‘heterozygous’, ‘dominant’ and ‘recessive’ with respect to genetic inheritance. 5
2.3 I can use and interpret a Punnett square to identify possible genotypes and phenotypes of offspring. 20, 23
2.3 I can explain sex linkage. 11, 19
2.3 I can distinguish between codominance and incomplete dominance.22
2.3 I can use a pedigree diagram to determine the type of inheritance that is occurring. 19
2.4 I can explain the different types of mutations, including their causes and effects. 16
2.4 I can describe some ways in which DNA can be manipulated. 25 Scorcher competition
Data questions
A student prepared an onion root tip slide and examined the cells using a light microscope.
She recorded the number of cells in each stage of the cell cycle.
The table shows her results.
Remembering
1. State the name of the position on a chromosome where a particular gene is located.
2. Recall two autosomal recessive inheritable traits.
3. Recall the name of the enzyme that unwinds the DNA double helix during DNA replication.
4. Name the structure formed when DNA condenses and becomes visible before cell division.
5. Define the terms ‘homozygous’, ‘heterozygous’, ‘dominant’ and ‘recessive’.
6. Identify the parts of the nucleotide in the following figure.
7. State the location in the cell where transcription and translation occur.
Chapter checklists help students check that they have understood the main concepts and learning goals of the chapter.
Chapter review question sets are categorised under five headings: Remembering, Understanding, Applying, Analysing and Evaluating. These questions can be completed in the Interactive Textbook or downloaded as Word documents.
8. State how many chromosomes you would expect to find in:
She then calculated the mitotic index for different areas of the root tip. The graph shows her results.
a) a human somatic cell
b) a human gamete
c) a somatic cell of a human with Down syndrome.
1. The mitotic index of dividing tissue is calculated with the following formula: Mitotic index = number of cells seen that were undergoing mitosis
Calculate the mitotic index of the tissue shown in the table.
2. The duration of any phase of the cell cycle can be calculated with the following formula:
The cell cycle duration for the onion is 24
Calculate the duration of metaphase.
3. Identify the trend shown in the graph.
4. Extrapolate the data in the graph to estimate the mitotic index of the cells found 2 mm from the root tip.
Data questions help students apply their understanding, as well as analyse and interpret different forms of data linked to the chapter content. These questions can be completed in the Interactive Textbook or downloaded as Word documents.
STEM activities encourage students to collaboratively come up with designs and build solutions to real-world problems and challenges.
VIDEO
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WIDGET
These icons indicate that there is an interactive widget in the Interactive Textbook.
These icons indicate that worksheets, activities or question sets can be downloaded from the Interactive Textbook. DOC
QUIZ
Automarked quizzes can be found in the Interactive Textbook for every section.
SCORCHER
Competitive questions can be found in the Interactive Textbook for every chapter review.
These icons indicate that questions can be completed in workspaces in the Interactive Textbook.
The Interactive Textbook (ITB) is an online HTML version of the print textbook, powered by the Edjin platform. It is included with the print book or available as a separate digital-only product.
Definitions pop up for key terms in the text.
Quizzes contain automarked questions that enable students to quickly check their understanding.
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Practicals are available as Word document downloads, with sample answers and guides for teachers in the Online Teaching Suite.
Worksheets are provided as downloadable Word documents.
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Self-assessment tools enable students to check answers, mark their own work and rate their confidence level in their work. Student accounts can be linked to the learning management system used by the teacher in the Online Teaching Suite.
The Online Teaching Suite (OTS) is automatically enabled with a teacher account and is integrated with the teacher’s copy of the Interactive Textbook. All the assets and resources are in one place for easy access. The features include:
• the Edjin learning management system with class and student analytics and reports, and communication tools
• teacher’s view of students’ working and self-assessment
• chapter tests and worksheets as PDFs and as editable Word documents with answers
• editable curriculum grids and teaching programs
• teacher notes (including suggested responses if relevant) for Practicals, Try this, Making thinking visible, Explore! and STEM activities
• adaptive tools, including ready-made pre- and post-tests and intuitive reporting.
Scientists ask questions about the world around them and follow a systematic process, known as the scientific method, to find answers. In this chapter, you’ll learn how to think like a scientist by developing clear, testable hypotheses, making reasoned predictions and asking questions that can be investigated. You’ll also explore how to plan and carry out fair, reproducible and ethical experiments that help you answer those questions. Finally, you’ll discover how to evaluate the quality of other scientists’ work, judging whether their findings are valid and reliable.
Questioning and predicting
Section 1.1
Section 1.2
Section 1.3
Section 1.4
The scientific method is a framework for research.
Planning and conducting
Processing and analysing
Evaluating and communicating
• Proposing investigable questions
• Identifying variables
• Forming hypotheses
• Making predictions
• Validity and reproducibility
• Safety and ethics
• Collecting data
• Accuracy and precision
• Types of data
• Calculating central tendency
• Displaying data
• Interpreting data
• Evaluating methods
• Evaluating claims
• Communicating effectively
• Line of best fit
• Interpolation
• Extrapolation
• Trends in data
Curriculum content
Propose
© School Curriculum and Standards Authority Glossary terms
At the end of this section, I will be able to:
1. Propose investigable questions and hypotheses to test relationships.
2. Describe the types of variables in scientific investigations.
Scientists observe the world around them and ask questions about what they see. To find answers, they follow a structured process called the scientific method. This method helps ensure that investigations are carried out in a logical and reliable way. In this section, you will explore the first steps of that process.
Observing and asking questions is the first step of the scientific method. Scientists gather information using all their senses: sight, hearing, smell, taste and touch. An observation is a statement about information gathered from the senses without any explanations or opinions, such as, ‘The sky is blue’, ‘The water is cold’, ‘The leaf has a rough texture’.
Once they have made an observation, scientists use inference to provide possible explanations based on their existing knowledge. For example, if you observe that the sky is overcast, you might infer that it will rain soon. An inference helps you to formulate an investigable question that can be answered by conducting an experiment, such as: ‘Does light intensity affect the rate of photosynthesis in plants?’ or ‘Does the temperature of water affect how fast sugar dissolves?’
Investigable questions are those that can be answered through scientific investigation or experimentation. These questions are specific, measurable and testable. The question, ‘How does light intensity affect the growth of plants?’ is investigable because it involves a variable (light intensity) that can be manipulated and measured (plant growth). To answer investigable questions, you need appropriate resources, such as equipment, materials and time.
inference the process of linking an observation with past knowledge and assigning meaning to the observation investigable question a research question that can be answered by conducting an experiment
On the other hand, non-investigable questions are those that cannot be answered through experimentation. They might be too broad, subjective or not measurable, such as, ‘Why are plants important?’ or ‘What is the best type of music?’. These questions might require background research or expert opinions rather than practical experiments. When considering which type of question to ask, it is important to think about the resources you have available, such as access to equipment, time constraints and the feasibility of carrying out the investigation. This helps ensure that the question you choose is appropriate for a scientific investigation.
Quick check 1.1
1. State the purpose of formulating an investigable question.
2. Provide an example of a non-investigable question related to plant biology.
3. If you observe that a liquid is boiling, state the type of inference you might make.
Before planning an experiment to answer a research question, scientists first look at what other scientists have already discovered about the topic. This is called a literature review. It is important because scientists can learn from the results and methods used in previous studies. By doing this, they can improve their own research, avoid repeating experiments that already have answers, and find new ideas to explore.
A literature review also helps scientists understand what challenges others have faced, what worked well, and what didn’t. This makes it easier to design experiments that are likely to succeed.
Most scientific research is funded by the government or private companies. To get funding, scientists need to prove that their research is important and useful. A good literature review shows why the work is needed, how it can solve real-world problems, and what new information it will provide. By building on past research, scientists can show that their project is worth supporting and can make an impact.
Science inquiry 1.1
Researchers have discovered that the native legume Crotalaria novae-hollandiae hyperaccumulates zinc by concentrating it in its tissues. They have speculated that this could enable phytomining, the process of harvesting substances from the living tissue of plants that act as hyperaccumulators. Such plants retain certain substances in particularly high concentrations after absorbing them through their roots. There are around 100 known hyperaccumulators, and the ash created when these plants are burned can be a ‘bioore’, often containing more than 25% metal.
These plants could potentially offer an environmentally friendly method of extracting valuable metals from mining waste materials, or of cleaning up soil contaminated with mining waste. This type of research could have a significant impact on the future of the metal industry, but it depends on researchers being successful in obtaining funds. To make this type of discovery, these researchers would have had to write applications for financial grants from government or, less commonly, from commercial entities. To successfully attract a grant, they have to provide compelling literature reviews and a well-designed project plan, and outline the likely future benefits of their findings for society.
1. Describe why a literature review might be important for a scientist seeking funding.
The purpose of an investigation is to answer a research question through systematic data collection and analysis. This helps scientists understand natural phenomena, test ideas or explore impacts in the real world. For example, an investigation into the effects of pollutants on local water quality might aim to find out how different contaminants affect aquatic ecosystems. Clearly defining this purpose ensures that the investigation stays focused and relevant.
In all investigations, the independent variable is the factor that is deliberately changed to observe its effect, such as the amount of sunlight a plant receives. The dependent variable is what you measure to determine whether it is affected by changes in the independent variable, such as the plant’s growth rate. Controlled variables are the factors that are kept constant to ensure a fair test and isolate the effect of the independent variable, such as using the same type of soil and plant species.
For example, in an experiment designed to test whether the amount of water affects plant growth, the independent variable would be the amount of water given to the plants, while the dependent variable would be the plant height measured. Controlled variables in this scenario might include soil type, plant species and light conditions, and the experimenter would ensure that these remain constant throughout the experiment.
Making thinking visible 1.1
think, pair, share: Research question
Consider the research question: Does light intensity affect the length of a bean sprout’s growth?
1. Think of as many variables as possible that would be required to be controlled in this experiment.
2. Pair up with a partner and share your list. Listen to your partner’s thoughts.
3. Share your combined list with another group in the class. Listen to the list that the other group came up with.
The Think, pair, share thinking routine was developed by Project Zero, a research centre at the Harvard Graduate School of Education
independent variable the variable that is deliberately changed during an experiment dependent variable the variable that is measured during an experiment (as it responds to the independent variable) controlled variable a factor that remains constant throughout an experiment, to ensure that any changes observed in the dependent variable are solely due to the manipulation of the independent variable fair test an experiment where all variables are kept constant except for the independent variable being tested
confounding variable an external factor that can unintentionally affect the outcome of an experiment, making it difficult to determine whether changes in the dependent variable are caused by the independent variable validity the extent to which an investigation accurately measures or tests what it was intended to measure or test qualitative a form of data that describes characteristics or qualities about something quantitative a form of data that is a numerical measurement field work practical work conducted by a scientist in a natural environment rather than in a laboratory precision how closely repeated measurements agree with each other hypothesis an educated guess that can be tested through further experimentation; plural hypotheses prediction a statement that describes what is expected to happen if the hypothesis is true
It is also important to identify and account for confounding variables. These are factors that might unintentionally influence the results, preventing you from identifying the relationship between the independent and dependent variables. In this experiment, potential confounding variables could include variations in temperature, differences in soil moisture content or even pests affecting plant health.
To decide whether an experiment has provided ‘valid’ results, the experimenter must consider the influence of any loosely controlled variable or confounding variables, rather than how much data was collected. If a confounding variable was not controlled in the method, the results might be ‘reliable’ but not ‘valid’. It is important that scientists are strict in controlling the controlled variables, to ensure validity of their results.
Different investigations require different types of data. Qualitative data is descriptive, like noting the colour or texture of plant leaves, while quantitative data is numerical, such as measuring the height or number of leaves. Choosing the right method to collect reliable data is also important. Field work, such as observing animals in their natural habitat, can provide real-world data, whereas laboratory experimentation, like testing chemical reactions under controlled conditions, ensures precision. For instance, if studying the effect of light on plant growth, laboratory experiments can control environmental factors with more precision than field studies.
Investigations often need to be modified in response to new evidence. If initial results suggest an unexpected trend, the hypothesis or experimental design might need to be adjusted. Say you are testing how different fertilisers affect plant growth and you discover that one fertiliser unexpectedly stunts growth. You might need to do some further investigation of the chemical composition of that fertiliser and its effect on the plants.
1. Identify whether you would use qualitative or quantitative data to describe the colour of a plant’s leaves.
2. Identify an example of a controlled variable in an experiment testing the effect of light on plant growth.
3. Explain what a confounding variable is.
Stating a hypothesis and making predictions are key steps in scientific investigations. A hypothesis is an ‘educated guess’ based on existing knowledge, written as a testable statement, such as: ‘If plants receive more water, then they will grow taller’.
A prediction describes what is expected to happen if the hypothesis is true. It guides the experiment’s design and data collection. For example, ‘Plants watered daily will grow 5 cm taller in a month compared to those watered weekly’.
Try this 1.1
Two students had the research question ‘Does light intensity affect the length of a bean sprout’s growth?’
They were thinking of setting this experiment up under three different conditions: darkness, ambient light and a greenhouse setting.
1. State the independent variable for this experiment.
2. State the dependent variable for this experiment.
3. Write an appropriate hypothesis for this investigation using an ‘If … then …’ statement.
4. List four variables that must be controlled in this experiment.
5. What assumptions might have been made in this experiment regarding controlled variables?
6. How might the results of this experiment lead to further hypotheses and testing?
Section 1.1 questions
Remembering
1. Recall the primary purpose of conducting background research before designing an experiment.
2. Define the term ‘controlled variable’.
Understanding
3. Describe an investigable question.
4. Explain why it is important to identify and account for confounding variables in an experiment.
Applying
5. You are investigating the effect of different types of soil on plant growth. If you use three types of soil and measure the height of the plants, identify the independent and dependent variables.
6. Describe how a literature review could influence the design of your experiment.
7. Create an investigable question related to the effects of pollution on water quality.
Analysing
8. Explain how the process of stating a hypothesis differs from making a prediction in scientific investigations.
9. Discuss how confounding variables might affect the validity of an experiment. Provide an example related to plant growth.
Evaluating
10. Given the information that a research study found that increased nitrogen levels lead to greater plant growth, propose an appropriate hypothesis to further test this finding
11. Assess the importance of proposing clear investigable questions in scientific research.
At the end of this section, I will be able to:
1. Define ‘validity’ and ‘reproducibility’.
2. Explain the importance of managing risks and ethical considerations.
3. Collect and record data with precision.
Once a scientist has formed a hypothesis, the next step is to test it through a scientific investigation. This involves following a series of structured steps to ensure that the results are valid and reliable.
Selecting suitable materials and technologies is essential for the success of an investigation. Choosing high-quality and appropriate tools, such as using a pH meter for accurate acidity measurements, ensures reliable and valid results.
Accurately assembling, constructing and manipulating equipment will improve any investigation. This involves setting up experimental apparatus according to detailed instructions and ensuring all components function correctly. For instance, when assembling a circuit for an electrical experiment, the wires must be connected properly and the power supply must be compatible with the components used.
Manipulating equipment with precision, such as adjusting the flame of a Bunsen burner or calibrating a digital scale, ensures that the experimental conditions are consistent and reliable. Calibration is the process of adjusting equipment to ensure its measurements are accurate and consistent. This procedure involves comparing the measurements from the equipment with known standards or reference values and making necessary adjustments to correct any discrepancies.
1.8 When conducting scientific experiments in challenging environments (like the Snowy Mountains, shown here), proper set-up and handling of equipment are crucial for obtaining accurate results.
Ensuring all equipment is correctly calibrated will allow better replicability and reproducibility by other scientists. Personal error in taking measurements (e.g. taking readings on glassware from a steep angle, or a slow reflex time when stopping a stopwatch) can reduce the reliability of results. Repeating the experiment multiple times and averaging the results can reduce the impact of errors. Using and maintaining equipment properly can also enhance the accuracy of results and prolong the lifespan of the tools and materials used.
Following the planned procedure methodically is important for experimental validity. This involves following the step-by-step instructions outlined in the experimental design and being vigilant for any deviations or errors that may occur. If an error is identified, such as an unexpected change in temperature or a malfunctioning piece of equipment, it is important to pause the experiment, assess the situation and take corrective action. This may involve recalibrating equipment, repeating certain steps, or adjusting the procedure to account for the error. Documenting any deviations and the actions taken to address them is important for maintaining the integrity of the investigation and providing a clear record for future reference.
In any scientific investigation, you must identify any potential risks, to ensure the safety of all participants. Risks can include physical hazards, such as exposure to harmful chemicals, or environmental hazards, such as those affecting local ecosystems. If you were conducting field work in a river to study water quality, risks might include slippery surfaces, strong currents and the presence of dangerous wildlife.
To manage these risks, safe work practices should be implemented. This includes wearing appropriate personal protective equipment (PPE), such as gloves, safety glasses and lab coats, when handling hazardous materials, as well as following safety protocols to reduce the chance of accidents.
replicability how well the results match up when a different scientist repeats the experiment under the same conditions as the original experiment, including the same equipment and laboratory or field site reproducibility how well the results match up when a different scientist repeats the experiment under different conditions than the original experiment, including different equipment and laboratory or field site reliability how repeatable, replicable and reproducible the results are
Managing risks includes having emergency procedures in place, such as knowing the location of safety showers and eye wash stations. Addressing potential risks and following safety guidelines reduces the likelihood of accidents and injuries.
Figure 1.10 Proper use of personal protective equipment, such as radiation protection suits, is necessary to maintain safety while handling hazardous materials. informed consent when participants are informed about the risks and procedures involved in an experiment and they sign to say they agree to participate ethics the standards used to appraise and guide what is considered acceptable conduct
Figure 1.11 Effective risk management involves ensuring that emergency procedures, like the location of eye wash stations, are well known and accessible.
Alongside safety, ethical issues must also be considered, especially when working with living organisms or human subjects. Ensuring that no harm comes to participants and obtaining informed consent are fundamental principles of ethics.
1. State what you should do if you identify an error during an experiment.
2. Identify an example of personal protective equipment (PPE) that should be worn when handling hazardous materials.
3. Explain why it is important to select high-quality and appropriate tools for an investigation.
Experiments come in various forms, and you may already be engaging in experimentation in your daily life! However, for scientific investigations to yield meaningful results, they should always be conducted in a controlled environment, where only the independent variable is altered and the dependent variable is measured.
While experiments are often performed in laboratories, there are times when scientists must work in the field. Field work involves gathering evidence in real-world settings, outside the controlled conditions of a laboratory. This presents challenges, because scientists in the field cannot manipulate environmental factors or control confounding variables, and this makes it more difficult to establish causal relationships.
There are various reasons for conducting field work. Astrophysicists, for instance, may travel to remote astronomical observatories, such as the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory in Sierra Negra, Mexico. Environmental chemists often conduct field work to assess the presence and impact of chemicals in natural ecosystems. Similarly, marine biologists may need to locate, tag and track marine animals during their migratory movements. Through such field investigations, scientists gain valuable insights that contribute to our understanding of the natural world.
It is important to consider sample size in any experiment, because it can affect the accuracy and reliability of the results obtained. The amount of data needed to produce a useful sample size depends on several factors, but in general a larger sample size will give more accurate and reliable results. This is because a larger sample size reduces the effect of random error. However, a larger sample size may not always be necessary or feasible, particularly in cases where the data is highly consistent, or there are experimental or financial limitations.
Wherever the experiment is done, data collection and recording involves using appropriate methods and tools to ensure all measurements are precise and consistent. For example, when measuring the growth rate of plants, it is important to use a consistent method, such as measuring from the base to the highest point of the plant at regular intervals. With field work, documenting the conditions under which the data was collected, such as the date, time and environmental factors, can also provide valuable information when interpreting the results later.
accuracy
how closely a measurement matches the ‘true’ or accepted value
systematic error
an error that occurs due to a poorly calibrated device
(giving consistently high or consistently low measurements)
outlier
an anomalous data
value that does not seem to fit with the rest of the data
Experimental accuracy refers to how closely the experimental results match the ‘true’ values. If, for instance, you record the volume of water in a measuring cylinder to be 20 mL, but it actually provides 21 mL, then your measurement might be considered inaccurate. Choosing the best equipment and using a method that avoids systematic errors will improve the accuracy of the experiment. For example, you could use an electronic timer system to record measurements at given time intervals rather than rely on a human using a hand-operated stopwatch.
Experimental precision refers to how closely repeated measurements agree with each other. Suppose you record the mass of a product of a chemical reaction in grams and you repeat the experiment four times, getting results of 1.54 g, 1.55 g, 1.55 g and 1.54 g. This data shows low variation from the mean (it is clustered tightly) and can be said to be precise. However, even though this data is precise, it is not necessarily accurate. Precision does not indicate how ‘true’ the data is; that is, it does not indicate how accurately the data matches the actual values. Precision can be affected by how the experimenter reads the values on glassware, such as burettes and measuring cylinders, particularly when they need to estimate a value between the graduated markings.
Figure 1.14 A faulty piece of measuring equipment might consistently give wrong values, like the target on the left. This measurement is precise, but the results are inaccurate and do not measure what they claim to measure; therefore, they have low validity.
Outliers are anomalous data values that do not appear to fit with the other recorded values. These values are often a long way from the mean and may represent an experimental error, such as error in reading the scale or a fault in the measuring equipment.
It is important to investigate outliers and account for them in the discussion of your results. Sometimes, repeating the experiment eliminates the outlier, but if you do this, you need to mention that this has occurred. The most common causes of outliers in a data set in a scientific laboratory are:
• data entry errors (human miscalculation)
• inaccurate measurements (instrument error).
Figure 1.15 Outliers (such as the data point in red) are often easily spotted once the data has been plotted on a graph.
Outliers can easily be spotted when the data is graphed. There will often be a large gap between an extremely high or low value and the rest of the observations, indicating that it differs greatly.
1. Suggest how a systematic error could affect your experimental results.
2. Define the term ‘outlier’ in your own words.
Section 1.2 review
Online quiz
Section questions
Remembering
1. Define ‘validity’.
2. State what is meant by experimental accuracy.
Teachers can assign tasks and track results
3. Name one reason why it is important to follow planned procedures in an experiment.
4. Describe the process of calibration in relation to scientific equipment.
Understanding
5. Explain why it is necessary to use appropriate tools and methods when collecting data.
6. Describe how the presence of an outlier affects the interpretation of the data.
7. Explain the differences between accuracy and precision in experimental measurements.
Applying
8. If you notice that your digital scale is giving slightly different readings for the same weight, identify what you should do.
9. When measuring the growth rate of plants, plan how your method should be consistent.
10. When doing field work to assess the impact of chemicals in an ecosystem, identify the safety measures that should be implemented.
Analysing
11. Compare the effects on experimental accuracy of using a hand-operated stopwatch versus an electronic timer system.
12. If repeated measurements of a chemical reaction’s mass are very close but consistently slightly off from the true value, infer what this means.
13. Discuss the relationship between sample size and reliability in experimental results. Why is a larger sample size generally advantageous?
Evaluating
14. Discuss why documenting conditions such as date, time and environmental factors is important for field work data.
15. Propose some ethical issues that must be considered when conducting an experiment about how sleep deprivation affects Year 9 students’ exam scores.
Go online to access the interactive section review and more!
continuous data
quantitative (numerical) data points that have a value within a range; usually measured against a scale that includes decimals or fractions (e.g. length in metres)
discrete data
quantitative (numerical) data points that tend to be whole numbers; usually counted (e.g. number of pets)
ordinal data qualitative (categorical) data where the categories have an order (e.g. days of the week)
nominal data qualitative (categorical) data where the categories have no clear order (e.g. colours)
mean the average value, found by adding all the numbers together and dividing by the count of numbers
median the middle value in an ordered data set, or the average of the two middle values if the set has an even number of observations
At the end of this section, I will be able to:
mode
the most frequently occurring value in a data set
range the difference between the highest and lowest values in a data set
1. Calculate the mean, median, mode and range of a data set.
2. Use appropriate representations to organise data and information.
3. Construct graphs to organise and analyse data.
Once data has been collected during an investigation, the next stage is to organise and examine it. Scientists process the data to identify patterns, trends and relationships that might help answer their research questions or support their hypotheses.
Types of data
Quantitative data is numerical, and can be categorised as either continuous or discrete. Continuous data tends to include all numerical values within a range and is often measured. Discrete data consists of exact values such as integer numbers (whole numbers) and is often counted.
Qualitative data is data that is worded, descriptive or categorical. It can be categorised as either ordinal or nominal. Ordinal data has a clear order to the categories, whereas nominal data has no clear order to the categories. Some examples are shown in Figure 1.16.
Quantitative (numerical) ContinuousDiscrete
Examples:
• time in seconds
• volume in millilitres
• height in metres
Examples:
• number of students in the room
• score rolled on a die
• frequency of an event
Qualitative (categorical)
Examples: • colours • breeds of dog • gender
Ordinal
Examples:
• subjective ratings, such as small, medium or large
• day of the week
When interpreting the results of your scientific investigation, organising the data effectively will enable you to draw accurate conclusions. Large data sets often require ‘data cleaning’. This means removing duplicates, addressing missing values and correcting errors, to maintain the quality of the data. Descriptive statistics are used to summarise and describe the key features of a data set. They include measures of central tendency (the mean, median and mode), which provide a ‘central’ value for comparison, and measures of variability (the range), which show how spread out the data is. The mean is used to measure the centre of a quantitative data set. It is the most common statistic used to represent an average. The mean is the sum of all the values collected, divided by the number of values:
Mean sum of all data values number of data values
However, the mean may not be a fair representation of the data, because the mean is heavily influenced by outliers – values that are either very large or very small. The median is an alternative way of measuring the centre of your data. In a set of data, the median is the value where an equal number of data points sit above it and below it. Think about the median strip in the centre of a major highway. It is in the middle, with the same number of lanes on either side. The median is the true middle of the data and is a good measure of the average when your data includes outliers. The mode is the most frequently occurring value or values in a data set. The range is the difference between the highest and lowest values in a data set. It can be calculated using the following equation:
Worked example 1.1
To determine how light affects plant growth, Jedda creates three groups, each consisting of 10 plants, and measures their growth rates (in cm/week). The data is recorded in the table.
Growth rates of 10 plants under different light conditions
Group Light conditions
Growth rate (cm/week)
APlants grown under natural sunlight5, 6, 7, 5, 6, 8, 7, 5, 6, 7
BPlants grown under LED lights 7, 8, 7, 8, 9, 8, 7, 8, 9, 7
CPlants grown under fluorescent lights4, 5, 4, 5, 6, 5, 4, 5, 6, 4
Calculate the mean, mode, median and range for each group.
Working
Group
Explanation
Calculating the mean
To calculate the mean, add up all the values, then divide the result by the sample size (the number of plants), which in this case is 10 for each group.
Calculating the mode
Group A mode = 5, 6, 7 (all appear 3 times each)
Group B mode = 7, 8 (both appear 4 times each)
Group C mode = 4, 5 (both appear 4 times each)
Group A: 5, 5, 5, 6, 6, 6, 7, 7, 7, 8
Median = (6 + 6) 2 = 6
Group B: 7, 7, 7, 7, 8, 8, 8, 8, 9, 9
Median = (8 + 8) 2 = 8
Group C: 4, 4, 4, 4, 5, 5, 5, 5, 6, 6
Median = (5 + 5) 2 = 5
The mode is the most frequently occurring value. In this case, each group has multiple modes.
Calculating the median
To find the median, first arrange the values in ascending order. Then identify the middle value. Because there is an even number of values in each group, the median is the average of the 5th and 6th values.
Group A = 8 – 5 = 3
Group B = 9 – 7 = 2
Group C = 6 – 4 = 2
To calculate the range, subtract the smallest value from the largest value.
There are many benefits of analysing descriptive statistics. These statistics provide a clear summary of the data set, and this helps in recognising patterns within the data, making it easier to communicate these patterns to others. In Worked example 1.1, calculating the mean and median growth rates makes it easier to compare the growth of the plants under different light conditions. Group B shows the highest growth rates, suggesting it performed best under the given conditions, probably due to the LED lights. Group A has the highest range, which shows more variability in growth. Group C has the lowest mean growth rate.
Consider the following data set: 17, 14, 18, 21, 21, 19, 12, 20, 16.
1. Calculate the mean, median, mode and range of the data.
2. Put the data into spreadsheet software and explore how you can determine the mean, median, mode and range of the data using analysis from the software.
Scientific notation is a commonly used system in science for writing numbers. It involves writing a number as a coefficient multiplied by a power of 10.
As an example, the number 0.0000123 can be written in scientific notation as shown in Figure 1.17.
Coefficient
Exponent (or power)
1.23 × 10 –5
Base
Figure 1.17 To write 0.0000123 in scientific notation, the decimal is moved backwards five places, so the exponent is –5.
When recording data values, it is important to use appropriate scientific notation to reflect the precision of the measurements. For very small or very large numbers, scientific notation can help to make the values more manageable and easier to read. It also allows us to represent the precision of the measurements concisely.
Consider a measurement of 0.0062 grams. This value can be written as 6.2 × 10–3 g, which indicates that the measurement is accurate to two significant figures. If we were to record the measurement as 0.006 g (i.e. using one significant figure), we would be losing precision and potentially introducing error into our data.
A variety of representations can be used to organise and present data, including graphs, keys, models, diagrams, tables and spreadsheets. The type of representation used depends on the type of data, and the target audience you are communicating the data to. Table 1.1 outlines some examples of data representation.
representation
Example
Bar graphsIdeal for comparing groups. The independent variable is plotted on the x (horizontal) axis. The dependent variable is plotted on the y (vertical) axis.
Line graphsIdeal for displaying changes over time. The independent variable is plotted on the x (horizontal) axis. The dependent variable is plotted on the y (vertical) axis.
Maximum average temperature in cities in WA
Perth
Kalgoorlie
Albany
Port Hedland
Kununurra
Type of data
representation
Pie charts Useful for showing proportions.
Example
Figure 1.21 The proportions of the 2023/24 ACT budget spent on different services
Keys and models Can represent biological processes or chemical reactions visually, helping to simplify complex information. Useful for communicating complex ideas to the general public (e.g. in a science museum).
Patagotitan mayorum
Paraceratherium transouralicum
10 m
Palaeoloxodon recki
African Elephant (Loxodonta africana)
White Rhino (Ceratotherium sinum)
Giraffe (Giraffa camelopardalis)
Polar Bear (Ursus maritimus)
Figure 1.22 Comparable sizes of various large land animals (living and extinct) and humans
Spreadsheets Essential for organising large data sets and doing calculations efficiently. Allow scientists to present data clearly and effectively, facilitating understanding and communication of their findings.
Figure 1.23 Using a spreadsheet on a computer to analyse data
An x–y scatter plot is one of the most common representations used to identify the relationship between two variables. The data is displayed on a Cartesian plot – this is a type of graph that has an x-axis (horizontal) and a y-axis (vertical), and each plotted point consists of a pair of numbers. The first number is the x-axis value and the second number is the y-axis value.
A scatter plot can be used for discrete or continuous quantitative data and consists of the following parts:
• The x-axis is the bottom horizontal part of the graph. It contains the data from the independent variable. These are the numbers that were changed in the experiment. They are not affected by the other variables. For example, the x-axis could show the time the experiment ran for, or the mass of substance used as a reactant.
• The y-axis is the vertical side of the graph. It represents the dependent variable. These numbers are a result of changes to the independent variable.
It is important to place the numbers on the x-axis and the y-axis in a way that shows the correct relationship. The numbers on both axes should increase evenly, and they usually start at zero as the corner point (origin). Each unit of distance on the line should represent the same value of the data. If, for example, the first unit of the graph represents five kilograms (kg), every increment of the graph also has to represent five kilograms (see Figure 1.24).
To plot points on the graph, place a dot or cross at the intersection of the two numbers. If plotting more than one variable, you can use different shapes (e.g. squares, stars, closed circles, open circles) to distinguish the points.
Aim to make the graph as large as possible – at least half a page is a good guide. This will make the data clearer and easier to use when doing your analysis. Also, wherever possible, draw all parts of the graph in pencil only, to make it easier to correct any mistakes.
Once the data points are plotted, they can be further analysed in terms of correlation. Figure 1.25 shows the results of an investigation into plant height over 25 days. Only the averages are shown. Plotting the data correctly on a Cartesian plane makes it easier to analyse.
Independent variable on left, dependent on right
Each pair of values represents one data point on the line graph located at (x, y), e.g. (25, 23.5)
Dependent variable on y-axis, labelled with units
Clear title
Figure 1.25 Mean plant height over time, presented in a table and a graph
Independent variable on x-axis, labelled with units
A study was conducted to investigate how the amount of plant food added affects plant growth in an aquarium. Eight aquariums (A–H) containing aquatic plants were set up in a laboratory. Food was added to each aquarium each day, in the amounts shown in the table below. After 3 weeks, the increase in mass of plants in each aquarium was measured. The results are shown in the table.
1. Identify the independent variable in this experiment.
2. Identify the dependent variable in this experiment.
3. Use this information to draw a complete x–y scatter plot of this data.
4. List three common tools or representations used to organise and present data.
5. Explain how the mean and range of a data set provide insights into the data’s central tendency and variability
Line of best fit
It may be difficult to see how the variables relate to each other on a scatter plot, especially when there are many data points. A ‘line of best fit’, also known as a trend line, can be drawn to represent all the points. The line is drawn so that it goes through the points as accurately as possible. It may touch some, all, or even none of the data points. The line is sometimes linear (straight) but it may also be non-linear by making it a curve. Drawing a line of best fit allows scientists to look for a general trend in the data being analysed.
There are some general rules for drawing a line of best fit.
• Do not include outliers.
• Make the line as close to as many points as possible (see Figure 1.26). Line of best fit
Figure 1.26 A scatter plot with a line of best fit. Even though the line is not touching any of the points, it is drawn as close to all the points as possible.
Figure 1.27 is an example of when a non-linear line fits the data points better than a straight line. In these cases, you can use a software program such as Microsoft Excel or a website such as Desmos to find the line of best fit.
Figure 1.27 The data points here suggest that the relationship between the x and y variables is non-linear. This means the line that best fits the data is curved, like graph (b), rather than straight, like graph (a)
interpolation the method of estimating unknown values within the range of known data points
extrapolation predicting values outside the range of known data points, based on the existing trend
correlation the relationship between two variables
Graphing data allows scientists to visualise relationships between variables and to make predictions. Interpolation involves estimating values within the range of observed data points (see Figure 1.28a), while extrapolation extends predictions beyond the observed range (see Figure 1.28b). Suppose a graph shows a linear increase in enzyme activity with increasing temperature up to 40°C. Interpolation can be used to estimate enzyme activity at 35°C, and extrapolation might predict activity at 45°C. These techniques are valuable for making informed predictions and understanding trends beyond the collected data.
growth (mm)
Interpolation (predicting inside the data set)
Extrapolation (predicting outside the data set)
growth (mm)
Figure 1.28 Predicting values using (a) interpolation versus (b) extrapolation
Identifying patterns and trends in data is necessary to understand the underlying phenomena in scientific investigations. Patterns are regularities or repeated sequences in data, while trends are a general direction in which data points move.
The relationships between variables should be described. This involves examining how changes in one variable affect another variable. For instance, in a study examining the effect of fertiliser on plant growth, the amount of fertiliser used (independent variable) and the height of the plants (dependent variable) are the key variables. A positive relationship might be observed if increased fertiliser leads to taller plants, while a negative relationship would occur if the fertiliser harmed the plants.
When interpreting a correlation between variables, it is important not to assume that one variable is having an effect on the other. A correlation may actually be caused by a confounding variable. That is why it is important to use the word ‘suggests’ rather than ‘proves’ or ‘causes’ when talking about possible relationships between variables. Table 1.2 outlines different types of correlation.
Correlation
Example graph
Positive (one variable increases as the other variable increases) Tree growth (mm) Rainfall (mm)
Negative (one variable decreases as the other variable increases) Tree growth (mm)
No correlation (no pattern in the way the variables increase or decrease) Tree growth (mm)
Interpretation
The results suggest that more rainfall may contribute to an increase in tree growth in a specific area.
The results suggest that increased salt added to the soil in a specific area inhibits (hinders) tree growth.
The results suggest that a tree’s growth is not affected by its distance from a lake.
1.2 How x–y scatter plots show correlation between two variables
1. State whether you would expect positive, negative or no correlation for each of the following examples.
a) The volume of a set of headphones, and hearing damage
b) A high temperature forecast, and the expectation of bushfires
c) Eating fatty foods, and having healthy cholesterol levels
d) Students’ absences, and their grades
2. Refer back to Quick check 1.6.
a) Predict whether the trend line for the graph you drew will be linear or non-linear.
b) Identify whether there is positive, negative or no correlation.
c) Describe what the data suggests would happen if you reduced the amount of food added.
d) Extrapolate the data to 5 weeks.
In a causal relationship, one variable directly affects another. This means that changes in the independent variable cause changes in the dependent variable. Establishing causality often requires controlled experiments, where the researchers can manipulate the independent variable and observe the resulting changes in the dependent variable.
In a correlational relationship, two variables are related, but this does not necessarily mean causation. In other words, while the variables may move together in a predictable pattern, this relationship does not establish that one variable causes the other to change. Correlation can be positive (both variables increase or decrease together) or negative (one variable increases while the other decreases).
A common misunderstanding is to assume that correlation equals causation. There are many examples where a correlation exists between two variables, but one variable does not cause the other to change. Other factors, often unmeasured or less obvious, might be influencing both variables. For example, increased ice cream sales correlate with increased drowning incidents. However, this does not mean that buying ice cream increases your risk of drowning! The correlation is due to higher temperatures driving increased ice cream consumption and increased swimming activity, which raises drowning risks.
Use the internet to research some more examples where correlation might not imply causation.
Remembering
1. Name four features of an x–y scatter plot.
2. Define the terms mean, median, mode and range.
3. Explain why data cleaning is important in data analysis.
4. Describe the role of significant figures in recording measurements.
Applying
5.
notation to the following numbers.
6. Classify the correlation between the variables in the following scatter plots.
7. Construct an x–y scatter plot of the following data from an experiment measuring the stretch in a spring with increasing masses added.
8. Construct an appropriate graph for the following data showing the temperature of water measured after every minute of heating.
Analysing
9. Contrast the benefits of using mean versus median when analysing a data set with outliers.
10. Explain how interpolation and extrapolation can be used to predict values in scientific experiments.
Evaluating
11. Evaluate the impact of outliers on the mean and median of a data set.
12. Examine a scenario that finds a correlation between the number of people who carry umbrellas and the number of traffic accidents. Why might this correlation be misleading?
primary data data that researchers collect themselves for a specific purpose; obtained from observations, experiments, surveys or interviews
At the end of this section, I will be able to:
1. Evaluate the validity and reliability of methods.
2. Evaluate the validity of conclusions and claims.
3. Communicate ideas, findings and arguments effectively.
When a scientist has conducted an investigation and analysed the data, the process isn’t over. The final stage involves communicating findings to others and reflecting on the quality of the investigation. Scientists evaluate their own work and the work of others to improve future experiments and ensure that results are trustworthy. This critical thinking helps science move forward.
To ‘evaluate the method’ means to critically analyse the reliability and validity of the experimental methods you used. To do this, examine the quality of the data you obtained, identifying outliers and explaining their presence. You should also address any issues that have arisen with the results, by considering the limitations of the equipment and the techniques you used.
Primary data is data collected directly by researchers for a specific purpose. To evaluate primary data, you need to evaluate both the validity and the reproducibility of the methods used.
‘Reproducibility’ refers to whether the same results can be obtained when different researchers repeat the study under similar or varied conditions. If different trials give different results, the reliability of the conclusions is called into question. Problems in validity or reproducibility can create significant gaps in the findings, so careful evaluation is necessary to ensure trustworthy results.
Assumptions made during research can affect the validity of the conclusions drawn. If, for instance, a researcher assumes that their study population (such as a specific type of plant) is representative of all plant species, the conclusions drawn may not be valid if they don’t apply universally. If a study on the effect of different fertilisers on plant growth uses only one species, such as a tomato plant, the findings may not accurately reflect the impact of fertilisers on other species. If a researcher assumes that a particular method of data collection (such as measuring plant height) is the best indicator of growth without considering other factors (such as leaf number or overall biomass), this could compromise the validity of the study.
It is crucial, therefore, to identify any assumptions made and evaluate their reasonableness. For instance, if a study assumes that a specific type of fertiliser significantly enhances plant growth without considering factors such as soil quality or watering frequency, the conclusions could be flawed. If there is limited evidence to support the claim that a certain fertiliser leads to better growth outcomes, this raises questions about the reliability of the findings.
When assessing assumptions, researchers must determine whether there is sufficient evidence to support their conclusions, or whether alternative explanations are possible. By critically analysing the context and the methodology, researchers can avoid potential pitfalls in their investigations.
Secondary data is information that has been collected by others for their own purposes, that is still relevant to your research. This includes data from published studies, government reports and various sources. When evaluating secondary data, it is essential to ensure that it does not contain personal information that could harm individuals, particularly sensitive data such as medical records or financial information. Before using secondary data, researchers should carefully review it to ensure that it has been anonymised – that is, identifying information has been removed.
It is important to cite secondary data correctly, to maintain academic integrity. Citing a source means identifying the original source of the data and providing accurate reference details in your report or publication. Failing to cite sources correctly can result in plagiarism accusations and damage the credibility of your research. Proper citations also allow readers to locate and verify the information cited.
When assessing the relevance of secondary data to your research question or claim, carefully review its quality, reliability and validity. To evaluate the validity of secondary sources, consider the:
• credibility of the data – examine whether it is from a reputable source and whether it provides references to support its claims
• currency of the information – to ensure that it is recent and relevant
• objectivity of the source – examine whether it has a particular bias that may influence the information presented
• methodology used – to ensure that there are no potential sources of bias or error in the data collection process
• consistency of the information – compared with other sources of information.
By critically evaluating both primary and secondary data, researchers can strengthen their investigations and contribute valuable insights to their field of research, with reliable and robust conclusions.
In 2018, a research paper was co-written by William McAuliffe, a psychology PhD student, in the esteemed journal Nature Human Behaviour. The paper suggested that people tend to become less generous over time when making decisions in an environment where they lack knowledge or interaction with others.
However, the university’s press department may have sought to increase the study’s appeal to news outlets by exaggerating its findings. The press release announcing the study’s publication carried the headline ’Is big-city living eroding our nice instinct?’
peer review a process where work is examined and approved by experts before being published randomised controlled trial a study design that randomly assigns participants to either an experimental group or a control group; the only expected difference is the variable being studied
Consequently, various media outlets picked up the story, with headlines such as ’City life makes humans less kind to strangers’ and ’Big city living “switches off human instinct to be nice”’. However, these interpretations of the study were inaccurate, as it was conducted in a lab, not a city, and only measured investment behaviour rather than overall kindness.
When reading reports of scientific studies in the media, it is important to evaluate the methods used by scientists to conduct their research to ensure the validity of the headlines. Here are some steps you can take when evaluating these factors.
1. Read beyond the headline. The headline of an article is designed to grab your attention, but it may not provide a complete or an accurate summary of the study. Read the full article to get a better understanding of the research and the methods used.
2. Check the source. Look for reputable sources of information, such as peer-reviewed scientific journals.
3. Look for replication. Scientific findings should be replicated by other researchers before they are accepted as true.
4. Check the sample size. Studies with larger sample sizes are generally more reliable than studies with small sample sizes.
5. Check the methodology. Look for studies that use rigorous methods to control for confounding variables and minimise bias. Randomised controlled trials are generally considered the best.
6. Look for limitations. No study is perfect, and there may be limitations to the methods used or the findings reported. Look for studies that acknowledge their limitations. Your teacher will provide you with headlines and the scientific report they are based on. Research the methods used by scientists in the provided studies and evaluate the validity of the headlines written in the media.
Quick check 1.8
1. Explain how primary data differs from secondary data.
2. Explain why it is important to evaluate the validity of secondary data.
An important part of writing a science practical report is evaluating your method and suggesting areas for improvement. Improving the quality of data collected during an investigation can enhance its reliability and validity. There are many ways to do this.
• Increase sample size – a larger and more diverse sample can give more generalisable results. If, for example, you are testing the effects of a fertiliser, including a range of plant species from different environments will provide more comprehensive understanding of the fertiliser’s effects.
• Ensure accurate measurements – using calibrated equipment for measurements and following standardised procedures will ensure that the data you collect is consistent.
• Minimise experimental errors – repeating measurements multiple times and calculating averages can help reduce random errors.
• Control confounding variables – ensuring that external factors, such as light exposure and watering frequency, are controlled throughout the experiment will help ensure that any observed effects are due to the independent variable being tested, and not other, unexpected things.
• Use valid data collection methods – choosing an appropriate method of collecting data that aligns with your research question will provide valid results.
In your conclusion, you should respond directly to your initial research question, indicating whether your hypothesis is upheld or not. Start with a broad summary of your findings, then back this up with specific data from your results. Use your scientific understanding to further explain your conclusions. For instance, understanding how photosynthesis works can help explain why increased light exposure enhances plant growth. Conclusions that you draw about your results should be directly supported by the evidence you collected during the investigation. Your conclusion should also support or refute your hypothesis – this is done by comparing the observed results with the expected outcomes based on your hypothesis.
1.31 If a hypothesis states that increased sunlight will enhance plant growth, data showing higher growth rates in plants exposed to more sunlight would support the hypothesis. If the data showed no significant difference or a decrease in growth, it would refute the hypothesis.
When you use information from other sources in your work, it is important to give credit to the original authors – this is known as referencing. Referencing shows where you got your information from and allows others to check your sources. When citing references and compiling a references list, you should use an accepted referencing style.
There are several common referencing styles you might use. The APA (American Psychological Association) style involves putting the author’s last name and the year of publication in parentheses when you mention their work in the text. At the end of your document, you create a reference list with all the details for each source, including the author’s name, the title of the work and the publication details.
Using the correct referencing style is important for several reasons. It helps you avoid plagiarism by giving proper credit to other researchers. It also allows others to verify your sources and check the information for accuracy. Proper referencing shows that you respect intellectual property and follow academic standards. Always be sure to use the style required by your school and use it consistently throughout your work.
1. Recall what plagiarism is, and why it is important to avoid it in research.
2. Describe how researchers can ensure that their conclusions are well supported by evidence.
Scientific texts can range from highly technical to more accessible, depending on their intended audience and purpose. A scientific paper published in a peer-reviewed journal will probably be written for a specialised audience of scientists, researchers and academics. These papers often use technical language and complex concepts that may be difficult for the general public to understand. In contrast, a popular science article or blog post will typically be written for a more general audience, with a focus on making complex concepts more understandable. These articles may include anecdotes or examples to illustrate key points, and they may be written in a more conversational tone. These articles try to engage and entertain the reader.
When comparing these types of texts, it is important to analyse how the author’s choice of language, tone and style affect the reader’s understanding and engagement with the topic. For example, a highly technical paper may provide an in-depth analysis of the data but non-expert readers may find it difficult to understand. A popular science magazine may be more engaging but will lack detail.
Acknowledging and communicating Aboriginal and Torres Strait Islander Peoples’ knowledge
Aboriginal and Torres Strait Islander communities hold important knowledge about their traditional culture, practices and history. Their understanding of the world comes from a strong connection to nature, developed over thousands of years through careful observation and experimentation. This is different from modern science, which uses strict methods of observation, experimentation and analysis to understand the natural world.
It is important for scientists to recognise the cultural value of traditional knowledge and to respect significant cultural sites, such as ceremonial grounds and traditional quarries, especially when they find artefacts during research. When traditional artefacts are discovered or when working in culturally important areas, scientists should engage with local Aboriginal and Torres Strait Islander leaders and relevant government agencies. Collaborating with these leaders helps ensure that scientists follow ethical guidelines when using traditional knowledge. Ignoring these guidelines can lead to cultural appropriation, where traditional knowledge is used without proper credit or permission, often leading to misunderstanding or misuse.
Understanding the link between Aboriginal and Torres Strait Islander knowledge and modern science creates a more inclusive approach to learning. This idea, known as working ‘both ways’, involves blending traditional knowledge with contemporary scientific methods, recognising the value of both perspectives.
When sharing knowledge from Aboriginal and Torres Strait Islander Peoples, it is crucial to be respectful and culturally sensitive. This means following cultural protocols and avoiding harmful stereotypes or language. It is usually best to seek permission from the relevant Aboriginal and Torres Strait Islander communities before sharing their knowledge. Being aware of the differences between various communities and languages, and using the correct terms when discussing specific cultural practices or beliefs, is also very important.
The Australian Government has made a significant shift by prioritising Indigenous knowledge in its updated National Science and Research framework. This marks the first time that Aboriginal and Torres Strait Islander knowledge systems will be integrated into scientific research and innovation efforts, particularly in emerging fields such as digital and data technologies. The move aims to protect and incorporate Indigenous cultural and intellectual property while advancing science.
The framework highlights five key priorities: transitioning to a net-zero future, supporting healthy and thriving communities, protecting and restoring the environment, building a secure and resilient nation, and elevating Indigenous knowledge systems. This integration is expected to address pressing challenges, including climate change and environmental degradation, by combining the deep environmental insights held by Indigenous Peoples with Western scientific approaches.
Indigenous rangers and UWA scientists are combining traditional knowledge and Western science to restore seagrasses in Shark Bay, Western Australia. Seagrass, vital for biodiversity and cultural heritage, has been severely affected by marine heatwaves. One approach involves transplanting healthy seagrass cuttings into affected areas, a labour-intensive process requiring divers to collect and replant the specimens. The second method uses a ‘seagrass snagger’, a device made from hessian fabric designed to slow down sand movement on the seabed. This allows seagrass seeds and fragments to become trapped, encouraging their growth in previously barren areas.
Online quiz
Section questions
Remembering
Teachers can assign tasks and track results
1. Identify the types of data that are considered primary and secondary in scientific research.
2. List common methods that researchers can use to improve the quality of data collected during an investigation.
Understanding
3. Explain how increasing sample size contributes to the reliability and validity of experimental results.
4. Describe the main factors to consider when evaluating the validity of secondary data.
Applying
5. Describe an example of how assumptions made during research can affect the validity of the conclusions drawn from a study.
Analysing
6. Analyse how biases in scientific studies might influence the interpretation of results.
Evaluating
7. Critique the method of using plant height as the sole indicator of plant growth in an experiment, highlighting the limitations of this approach.
8. Justify why it is essential to control confounding variables in an experiment and what the consequences of not doing so could be.
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Chapter checklist
Success criteria Linked questions
1.1 I can propose investigable questions and hypotheses to test relationships. 13, 14
1.1 I can describe the types of variables in scientific investigations.7
1.2 I can define ‘validity’ and ‘reproducibility’. 5
1.2 I can explain the importance of managing risks and ethical considerations. 3
1.2 I can collect and record data with precision. 9
1.3 I can calculate the mean, median, mode and range of a data set.11
1.3 I can use appropriate representations organise data and information.8, 15
1.3 I can construct graphs to organise and analyse data. 10
1.4 I can evaluate the validity and reliability of methods. 6, 12
1.4 I can evaluate the validity of conclusions and claims. 16
1.4 I can communicate ideas, findings and arguments effectively. 17
Scorcher competition
Review questions
questions
1. Recall why it is important to cite sources correctly.
2. State the purpose of extrapolation.
Data questions
3. Recall how chemical hazards should be addressed in experimental investigations. Understanding
4. Contrast primary data and secondary data, giving an example of each.
5. Define validity and reproducibility.
6. Explain why sample size is important in any scientific investigation.
7. Distinguish between the three types of variables.
8. The following data was obtained from a survey of the methods used to heat houses in a neighbourhood. Construct an appropriate representation for the data.
Applying
9. Sequence the instruments shown in Figure 1.33, from highest to lowest accuracy.
Analysing
10. A pathologist wanted to know the effect of adding an unknown substance X to bacteria. She conducted an experiment comparing bacterial colonies where the substance had been added to those where it had not been added. She then counted the number of colonies over a number of hours. The results are shown in the following table.
a) Construct a graph of the data and draw a line of best fit for each set of data.
b) Describe the two results in terms of correlation.
c) Determine the relationship between substance X and bacterial colony growth.
d) Using extrapolation, predict the number of bacterial colonies on day 10 if no substance X is added.
11. Two students wanted to determine the average price of milkshakes in Perth. They researched the prices of milkshakes from various cafes and compiled the data shown in the table. Calculate the mean, median, mode and range of the data set.
12. Evaluate the validity of the data when extrapolating from a graph.
13. Propose a hypothesis to test an identified relationship of your choosing.
14. Discuss why a scientific hypothesis must be able to be supported or refuted by evidence.
15. Deduce when a scientist might use a column graph rather than a scatter plot.
16. Discuss how the validity of media headlines can be evaluated.
17. Contrast the features of a peer-reviewed scientific journal article with those of a popular science article.
A Western Australian scientist designed an experiment to show how the temperature at which water boils changes as the water is placed at different heights above sea level. The scientist did this by boiling water while on a hike up Mount Meharry (also known as Wirlbiwirlbi to the local Indigenous Peoples) in Western Australia’s Karijini National Park. The mountain’s peak is 1249 m high and is Western Australia’s highest peak above sea level. The scientist used the same volume of water in the same beaker, the same heating apparatus and the same thermometer to measure the temperature. The results are presented in Figure 1.34.
1. Identify two controlled variables in this experiment.
2. Use the graph to determine the independent variable in the experiment.
3. Identify the trend in water boiling temperature as height above sea level changes.
4. Analyse the data points and identify any outliers that should be removed from the trend line.
5. From the trend line, infer the temperature of boiling water at 700 m above sea level on Mount Meharry (Wirlbiwirlbi).
6. Justify the claim that the linear trend line is a reliable fit for the data.
7. Extrapolate the data to estimate the height above sea level where water would boil at 95°C.
8. Calculate the range of the data presented.
9. Mountains in the Alps in Europe reach a height above sea level that is double that of Mount Meharry (Wirlbiwirlbi). Predict the temperature that water would boil at on a 2400 m peak in the Alps.
Organisms use various mechanisms to respond to environmental changes, ensuring their survival and stability. In humans, the nervous and endocrine systems regulate and coordinate the body’s responses to internal and external stimuli. Negative feedback is crucial in maintaining homeostasis, by counteracting the effects of fluctuations in the external environment. This chapter explores how the nervous and endocrine systems regulate responses to stimuli. It compares the temperatureregulation strategies of endotherms and ectotherms, and examines the role of negative feedback. It also investigates how plants use tropisms to adapt to their environment.
Endocrine system Body systems work together to maintain homeostasis.
Organisms respond to changes in the external environment.
Nervous system
Section 2.1
Section 2.2
Section 2.3
Animals can be classified according to how they respond to temperature.
Endotherms
• Birds
• Mammals
Ectotherms
• Reptiles
• Amphibians
• Fish
Plants respond to the external environment via tropisms.
• Phototropism
• Geotropism
• Hydrotropism
• Thigmotropism
• Chemotropism
• Heliotropism
Curriculum content
Biological sciences
Organisms have mechanisms to respond to changes in their environment; endotherms and ectotherms respond differently to changes in external temperature; tropisms help plants respond to external stimuli
• how endotherms, such as mammals and birds, and ectotherms, such as reptiles and fish, use heat transfer mechanisms to respond to changes in external temperature 2.1
• tropisms, such as phototropism, geotropism and hydrotropism 2.3
© School Curriculum and Standards Authority
Glossary terms
action potential auxin behavioural mechanism chemotropism conduction control centre convection ectotherm effector endocrine system endotherm geotropism heliotropism homeostasis hormone hydrotropism integumentary interneuron motor neuron negative feedback nervous system neuron neurotransmitter pathogen phototropism physiological mechanism radiation receptor reflex action response sensory neuron stimulus synapse target cell thigmotropism tropism
Learning goals
At the end of this section, I will be able to:
1. Describe organisms’ responses to external or internal stimuli.
2. Describe the relationships between body systems that are necessary to coordinate a response to stimuli.
3. Describe how endotherms respond to changes in temperature.
4. Describe how ectotherms respond to changes in temperature.
Coordination: It’s a team effort!
In the human body, eleven major organ systems work together to support growth, survival and reproduction. Each system relies on the others to maintain optimal function, with specialised organs performing distinct roles. In all multicellular organisms, body systems must coordinate to sustain life. Despite fluctuations in the external environment, the body effectively maintains a stable internal environment through homeostasis.
Homeostasis is essential for ensuring that the body’s internal conditions remain within the narrow range required for cellular and organ function. If these conditions are not maintained, enzymes can malfunction, disrupting cell processes and possibly causing severe health consequences.
Negative feedback mechanisms play a crucial role in maintaining homeostasis. These mechanisms operate by sensing when a system deviates from a set point, and then activating responses to counteract the deviation and bring the system back to its set point. It is called negative feedback because the response produced acts in the opposite direction to the change that was detected. In other words, the feedback negates or reduces the original stimulus, helping to restore balance. If there is a change in an animal’s external environment, such as a rise in temperature, the body must adapt to maintain a stable internal environment. In the human body, other physiological parameters that must be tightly regulated include blood glucose levels, blood pH and blood pressure.
Above normal level detected
Response triggered to reduce level to normal
‘Level’ of something Time
Below normal level detected Normal level
Response triggered to increase level to normal
To achieve homeostasis, the body responds to changes in its internal and external environment. A stimulus is any change in the environment that is detected by the body. The change can be physical or chemical. Stimuli include changes in temperature, light, sound, pressure and chemicals in the air or food.
stimulus a change in the environment that is detected by the human body; plural stimuli WORKSHEET
homeostasis the process in which an organism maintains a stable internal environment despite changes in the external environment negative feedback a regulatory process that reduces changes in a system, bringing it back to its normal state when it deviates from its set point
receptor a specialised structure that allows the body to detect and respond to stimuli
effector a muscle, gland or organ that carries out a response or an action in response to a stimulus
control centre often the brain or spinal cord, which receives signals from receptors and sends out signals to effectors to produce a response to a stimulus
response the reaction to a stimulus
Changes in the environment are detected by receptors in the body. If a response is required, certain actions are brought about by effectors within the body, to bring the body back to its ‘normal’ or optimum level.
Receptors are specialised structures in the human body that allow it to detect and respond to various stimuli. Receptors occur in all types of tissue, from the skin to the internal organs. There are many types of receptors, each specialised to detect a specific type of stimulus (see Figure 2.2). The different receptors are described in Table 2.1.
Vision
Photoreceptors detect light.
Touch
Mechanoreceptors detect mechanical forces such as pressure or movement. Thermoreceptors detect temperature changes. Nociceptors detect damage to body tissues, causing pain perception.
Olfactory chemoreceptors detect chemical stimuli.
Hearing
Mechanoreceptors detect mechanical forces from the vibrations conducted from the eardrum.
Taste
Gustatory chemoreceptors detect chemical stimuli.
Figure 2.2 The different sensory receptors associated with your five senses. Their shape is closely associated with their specialised functions.
Receptor typeLocation
Chemoreceptor
Stimulus
Blood vessels, brainChanges in blood chemistry (e.g. oxygen, carbon dioxide, pH levels)
MechanoreceptorSkin, muscles, joints, inner ear Physical distortion or deformation (e.g. touch, pressure, stretching, sound)
PhotoreceptorRetina of eye Light energy
ThermoreceptorSkin, brain Changes in temperature (e.g. heat or cold)
Olfactory receptorNose Chemicals in air (odours)
Gustatory receptorTaste buds on tongueChemicals in food and drink (taste)
NociceptorSkin, muscles, joints, organs Tissue damage or potentially harmful stimuli (e.g. heat, cold, pressure, chemicals)
Table 2.1 A summary of receptors in the body
When a receptor is activated, it sends a signal to the control centre, which is often the brain or spinal cord, to process the information and determine the appropriate response. The control centre then sends signals to the effectors, which are the organs, tissues and cells that carry out the necessary actions to produce a response to the stimulus.
The five-step stimulus–response model is shown in Figure 2.3.
Stimulus
Receptor
Making thinking visible 2.1
See, feel, think, wonder:
Taste buds
The tongue is a complex organ that contains various types of papillae, which house specialised sensory receptors known as taste buds. Papillae are small, raised structures on the surface of the tongue, and they can be different shapes and sizes. Taste buds play a crucial role in our sense of taste. The human tongue can contain thousands of taste buds, which detect different types of taste, such as sweet, sour, salty, bitter and umami (savoury). Each taste bud is made up of groups of specialised cells, called taste receptor cells, which are stimulated by different chemicals in the food we eat. When a taste receptor cell is activated, it sends a signal to the brain, which then translates the information into the sensation of taste. The location and number of taste buds varies from person to person, and can influence individual preferences for different types of food.
Taste hairs
Taste buds
Basal cell
Taste pore
Transitional cell
Gustatory cell
1. Define ‘homeostasis’.
2. Explain why homeostasis is so important for your survival.
3. Describe negative feedback.
Extracellular pH is the pH level in the extracellular fluid (fluid located outside cells in the body). This fluid surrounds the cells, providing them with nutrients and removing waste products. The normal extracellular pH range in humans is 7.35 to 7.45, which is slightly alkaline. The respiratory and renal systems maintain the pH of the extracellular fluid within this narrow range. Any deviations from this range can lead to various health problems and can even be life-threatening.
A key factor influencing extracellular pH is the level of carbon dioxide in the blood. Carbon dioxide is transported in the blood as bicarbonate ions and dissolved carbon dioxide. When carbon dioxide combines with water in the blood, it forms carbonic acid, which makes the blood more acidic. Therefore, regulating carbon dioxide levels is crucial for maintaining extracellular pH. To maintain the pH of blood within the normal range, the respiratory and renal systems work together to eliminate excess carbon dioxide from the body. The respiratory system increases the rate and depth of breathing, which increases the elimination of carbon dioxide through exhalation, which in turn reduces the carbonic acid in the blood. The excretory system also plays a role in regulating extracellular pH by excreting excess hydrogen ions or bicarbonate ions in urine.
Change in extracellular pH
Respiratory: increased rate and depth of breathing (to expel more CO2, reducing acidity)
Renal: excretion of H+ ions or reabsorption/secretion of bicarbonate (to balance pH)
Chemocreceptors (in blood vessels)
Respiratory system: lungs and associated muscles
Renal system: kidneys
Medulla oblongata (in brainstem)
A well-known response to changing light levels is the constriction or dilation of the pupil in the eye, which helps to control the amount of light that enters the eye. This response is controlled by a negative feedback mechanism – the constriction or dilation of the pupil is triggered by signals from specialised cells in the retina that detect changes in light intensity and send signals to the brain, which in turn sends signals to the muscles that control the size of the pupil. When exposed to bright light, the pupil constricts to reduce the amount of light that enters the eye; in low light, the pupil dilates to allow more light in (see Figure 2.8).
that can enter the eye by (a) constricting in bright light and (b) dilating in low light.
The body’s sleep–wake cycle is also closely linked to changes in light. The hypothalamus in the brain contains a specialised group of cells called the suprachiasmatic nucleus (SCN), which acts as the body’s master clock. The SCN receives information from the eyes about changes in light and uses this information to regulate the release of various hormones, such as melatonin, that help to control the sleep–wake cycle (see Figure 2.9).
Light-induced activation of SCN prevents the production of melatonin by pineal gland
Figure 2.9 The suprachiasmatic nucleus (SCN) triggers synthesis and release of the hormone melatonin by the pineal gland.
Changes in light can also affect mood and behaviour. Exposure to bright light can help to boost mood and increase energy levels, whereas exposure to low light can have the opposite effect, making people feel tired and lethargic.
Change in light intensity
In bright light: pupil constricts (circular muscles contract)
In dim light: pupil dilates (radial muscles contract)
Figure 2.10 Light stimulus–response model
Photoreceptors (rods and cones) in the retina
Circular and radial muscles of the iris
Midbrain
The fight-or-flight response is triggered by the release of stress hormones, such as adrenaline and cortisol, in response to perceived threats or stressors in the environment. These hormones increase heart rate and blood pressure, delivering more oxygen and nutrients to the body’s tissues to prepare the body for action. The rate and depth of breathing may also increase, to ensure there is enough oxygen in the bloodstream to support the increased activity. This response is regulated by negative feedback mechanisms, as the release of hormones eventually decreases, causing heart rate and blood pressure to return to normal levels.
Perceived danger or stress
Increased heart rate and blood pressure
Increased breathing rate and depth
Redirected blood
flow to muscles
Dilated pupils
Slowed digestion
Sensory receptors (e.g. in eyes, ears, skin)
Adrenal medulla (releases adrenaline and noradrenaline)
Various body organs, including heart, lungs, blood vessels and muscles
Figure 2.11 Danger stimulus–response model
Hypothalamus: activates the sympathetic nervous system and signals the adrenal medulla
pathogen any agent that can cause disease, such as bacteria, viruses or fungi
ectotherm
an organism that relies on external environmental sources of heat to regulate its body temperature endotherm
an organism that regulates its body temperature internally through metabolic processes, such as sweating, shivering or adjusting blood flow radiation the transfer of energy from a source without the involvement of particles
The body’s observable responses to the presence of pathogens, such as bacteria, fungi and viruses, are evidence of the immune response. These responses can include inflammation, fever, pain, swelling, and changes in behaviour such as fatigue and lethargy. Inflammation is a common response to infection by a pathogen – the body sends immune cells and fluid to the site of infection to help fight off the pathogen. Fever is another common response – the body raises its temperature to create an inhospitable environment for the pathogen. Once the pathogen is eliminated, negative feedback mechanisms cause the body’s immune response to decrease, returning it to its baseline state.
Presence of pathogens
Inflammation (swelling, redness, pain, heat at site)
Fever (raised body temperature)
Destruction or neutralisation of pathogens
Immune cells
White blood cells (e.g. neutrophils, T cells, B cells)
Hypothalamus (for fever regulation)
Damaged tissue releasing chemical signals (e.g. histamine)
2.13 Pathogen stimulus–response model
Immune system coordination centres, including lymph nodes and hypothalamus (especially for fever)
Figure 2.14 Fever is a physiological response to infection by pathogens such as viruses, bacteria and fungi.
Quick check 2.2
1. State the part(s) of the body that are involved in maintaining homeostasis.
2. Create a stimulus–response model similar to Figure 2.3, in your notes or on A4 paper, and annotate it with information about each of the five parts.
3. State the body systems that maintain the pH of extracellular fluid.
4. Describe how the eye responds to decreasing light levels.
An ectotherm is an organism that relies on external environmental sources of heat to regulate its body temperature, because it cannot generate sufficient internal heat. Reptiles, amphibians and fish are all ectotherms. They control their body temperature through behaviour, such as basking in the sun, moving into shade or burrowing into cooler areas. On the other hand, an endotherm is an organism that can regulate its body temperature internally through metabolic processes, such as sweating, shivering or adjusting blood flow. Mammals and birds are endotherms.
Ectotherms have a slower metabolism than endotherms, meaning they do not generate significant internal heat. Their energy comes mainly from external heat sources, such as the sun or warm surfaces. Because of this, they must use behavioural and physiological adaptations to control their temperature.
Ectotherms regulate their body temperature through different methods of heat transfer, because they cannot generate their own metabolic heat, as endotherms can. Ectotherms use radiation as a key source of heat, letting the sun warm their bodies. Many ectotherms, such as lizards and snakes, bask in the sun to raise their body temperature, which is essential for increasing their activity levels.
2.15 A Mertens’ water monitor (Varanus mertensi) basking in the sun. As an ectotherm, it relies on external heat sources to warm its body, which is essential for maintaining metabolic functions and activity levels.
2.16 The watjulum frog (Litoria watjulumensis) is a nocturnal tree frog found in northern Western Australia that thrives in warm, tropical environments. It regulates its body temperature by seeking shade during the day, and its moist skin allows evaporative cooling. At night, it absorbs heat from warm surfaces.
Conduction occurs when heat is transferred by direct contact with a surface. For example, a lizard lying on a warm rock absorbs heat from the rock, while a frog pressed against cool, damp soil loses heat to the soil.
Convection involves the transfer of heat through air or water movement. A breeze or flowing water can carry heat away from an ectotherm’s body, cooling it down. This is particularly important for aquatic ectotherms, such as fish, which experience heat exchange with their surrounding water (see Figure 2.17).
conduction the transfer of thermal energy through collisions between particles convection the transfer of thermal energy due to the movement of particles in a liquid or gas
behavioural mechanism
an action or response carried out by an organism to help maintain homeostasis and increase its chances of survival in a changing environment
Evaporation also helps to regulate temperature, because water loss from the skin or from respiratory surfaces removes heat. Amphibians, for example, can cool down through moisture evaporating from their skin.
Ectotherms can also use behavioural mechanisms to regulate their body temperature. Because they do not generate their own internal heat, they rely on their environment to warm up or cool down. Many species adjust their activity levels, positioning or habitat use to maintain an optimal body temperature for survival. The perentie (Varanus giganteus) (see Figure 2.18), Australia’s largest monitor lizard, basks in the sun during the morning to raise its body temperature, becoming more active as it warms up. However, during the hottest part of the day, it retreats to shaded areas or burrows to avoid overheating. This pattern of sunbathing and seeking shelter allows it to maintain an ideal body temperature for hunting and movement.
The western bearded dragon (Pogona minor) (see Figure 2.19) has the unique ability to change its body colour to assist with temperature control. In the cooler mornings, it darkens its scales to absorb more heat from the sun, helping it warm up quickly. As temperatures rise in the afternoon, it becomes a lighter colour, reflecting more sunlight to prevent overheating. This colour change reduces the energy and time needed for basking, allowing the bearded dragon to remain active for longer.
The pilbara olive python (Liasis olivaceus barroni), a nocturnal snake, uses its environment to regulate its temperature at night. After the sun sets, the rocks and surfaces that absorbed heat during the day remain warm. The python coils around these rocks to raise its body temperature, enabling it to stay active in cooler conditions. This behaviour is essential for hunting, as the python relies on maintaining a suitable temperature for muscle function and digestion.
Unlike reptiles, some aquatic ectotherms, such as the Western Australian dhufish (Glaucosoma hebraicum) (see Figure 2.20), regulate their temperature by adjusting their depth in water. Deeper waters are typically cooler, while shallower waters warm up more quickly. By moving between different depths, the dhufish can find a temperature that suits its metabolic needs. This behaviour is particularly important during seasonal changes, when surface water temperatures fluctuate significantly.
Endotherms are animals that can generate and maintain their own body heat through metabolic processes. This allows them to stay active in a wide range of temperatures, unlike ectotherms, which rely on external heat sources. Mammals and birds are endotherms; they regulate their body temperature by using physiological mechanisms and behavioural adaptations, such as:
• metabolic heat production – cellular respiration in the body generates heat, which helps maintain a stable internal temperature
• insulation – fur, feathers or fat help to trap body heat and reduce heat loss
• vasodilation and vasoconstriction – blood vessels dilate (become wide) to release heat, or constrict (become narrow) to retain heat
• sweating and panting – evaporation of sweat or moisture from the respiratory system cools the body
• shivering – rapid muscle contractions generate heat in cold conditions
• behavioural adaptations – seeking shade, burrowing, huddling or changing posture help manage heat exposure.
Change in external temperature
In cold conditions:
• shivering (muscle activity generates heat)
• vasoconstriction (reduces blood flow to skin)
Thermoreceptors in the skin and hypothalamus
• behavioural changes (e.g. huddling, burrowing)
• use of insulation (e.g. fluffing feathers, trapping air)
In hot conditions:
• sweating or panting (heat loss via evaporation)
• vasodilation (increases blood flow to skin)
• behavioural changes (e.g. seeking shade, spreading out)
Muscles, sweat glands, blood vessels, and behaviour
Hypothalamus
physiological mechanism an internal process or function carried out by the body to maintain homeostasis or respond to environmental changes
Many mammals and birds in Western Australia have adapted to cope with extreme heat and variable conditions. They use both physiological and behavioural strategies to cope with the intense heat, ensuring they can maintain their body temperature within a narrow range.
The red kangaroo (Macropus rufus) (see Figure 2.22) has adapted to the harsh conditions of the Australian outback by using its forearms to promote evaporative cooling. By licking its forearms, the kangaroo encourages moisture to evaporate, which helps lower its body temperature. Additionally, during the hottest parts of the day, the red kangaroo restricts its movement to conserve energy and avoid overheating.
The greater bilby (Macrotis lagotis) (see Figure 2.23), a nocturnal marsupial, avoids the extreme heat of the day. It remains hidden during the daytime, emerging only at night when temperatures are lower. Its large ears assist in heat loss, which helps to regulate its body temperature, allowing the bilby to maintain a stable internal temperature despite the intense daytime heat.
The emu (Dromaius novaehollandiae) (see Figure 2.24) has adapted to high temperatures by reducing its activity levels during the heat of the day. It also has loosely packed feathers that allow heat to escape more effectively, helping to prevent overheating. By staying relatively inactive during the hottest parts of the day, the emu conserves energy and avoids heat stress.
The western quoll (Dasyurus geoffroii) (see Figure 2.25) relies on burrowing to escape extreme surface temperatures. By spending much of its time in burrows, it can avoid the intense heat of the Australian summer. The quoll is most active at night, further conserving energy during the day and taking advantage of cooler temperatures at night for hunting and foraging.
These adaptations allow Western Australian endotherms to survive in hot, dry environments while maintaining a stable internal temperature.
In humans, the circulatory, integumentary, respiratory and muscular systems work together to regulate and maintain the body’s core temperature within a narrow range. If the core temperature begins to rise, thermoreceptors in the skin and in the hypothalamus detect the increase. Acting as both a receptor and an effector, the hypothalamus triggers several responses to cool the body. Sweat glands activate, releasing sweat onto the skin. As the sweat evaporates, it helps to cool the body. Blood vessels in the skin also undergo vasodilation, which allows more blood to flow to the surface of the skin, where it can release heat. These responses work together to reduce the body’s temperature back to its set point. The body’s observable responses to a drop in temperature are shown in Table 2.2.
Stimulus A change in the internal or external environment that triggers a response A sudden drop in external temperature
ReceptorSpecialised cells that detect the change and transmit a signal to the control centre
Control centre A structure in the brain (hypothalamus) that receives the signal and coordinates the response
EffectorThe muscles or organs that carry out the response
ResponseThe body returning to a state of balance so that the receptors are no longer active
Thermoreceptors in the skin and brain detect the drop in temperature and send a signal to the control centre.
The hypothalamus in the brain receives the signal and sends an electrochemical signal to the effector.
Muscles begin to contract and relax rapidly (shivering) to generate heat and increase the body’s core temperature.
The body’s temperature returns to within a normal range, and shivering stops. As the body warms up, the thermoreceptors detect the increase in temperature and signal the hypothalamus to reduce the response.
Hypothermia is a medical condition that occurs when the body’s core temperature drops below normal levels, typically below 35°C. It can occur if the body’s feedback systems fail to work properly.
For example, if the hypothalamus is damaged or not functioning correctly, it may not be able to detect changes in body temperature and adjust the body’s response accordingly. This can result in the body losing heat faster than it can produce it, leading to hypothermia.
2.27 Lambs born in colder areas are increasingly being outfitted with plastic raincoats. These lamb macs are designed to shield the lambs from harsh weather conditions and reduce their susceptibility to hypothermia.
Another way that disorders in feedback systems can lead to hypothermia is by disrupting the body’s ability to produce heat. For example, if the thyroid gland is not functioning correctly and not producing enough thyroid hormone, it can slow down the body’s metabolism, leading to a decrease in heat production. This can also result in hypothermia.
Hypothermia can also lead to some unusual behaviours. Conduct some research on paradoxical undressing and terminal burrowing.
Dogs don’t sweat, as humans do. Instead of sweating through their skin, dogs regulate their body temperature primarily through panting. When a dog pants, the evaporation of moisture from its tongue and respiratory tract helps to cool it down. This is why you’ll often see your dog panting after exercise or on hot days – it’s their natural way of cooling off.
Section 2.1 review
Online quiz
Section 2.1 questions
Remembering
Section questions
Teachers can assign tasks and track results
Go online to access the interactive section review and more!
1. Homeostasis is the maintenance of a relatively stable internal environment. Name four things that are tightly regulated in the human body.
2. State the normal pH range of extracellular fluid in humans.
3. State the difference between endotherms and ectotherms.
Understanding
4. Describe the negative feedback mechanisms that occur when the body’s temperature increases.
5. Describe how the respiratory system can control extracellular pH.
Applying
6. Construct a labelled diagram showing the stages of the stimulus–response model.
Analysing
7. Categorise the following organs as receptors or effectors.
a) hypothalamus
b) baroreceptors
c) liver
d) kidney tubules
e) pancreas
f) skeletal muscles
8. Categorise the following temperature regulation processes as typical of either endotherms or ectotherms.
a) shivering
b) behavioural adaptations (e.g. basking)
c) vasoconstriction
d) sweat production
e) hibernation
Evaluating
9. Evaluate the advantages and disadvantages of being an endotherm in environments with extreme temperatures.
10. Discuss the interdependence of various organ systems (e.g. circulatory, respiratory and excretory systems) in maintaining homeostasis.
WORKSHEET
neurotransmitter
a chemical messenger that transmits a signal across a synapse from one neuron to another cell, which may be another neuron, a muscle cell or a gland
neuron a nerve cell
nervous system the body system consisting of the brain, spinal cord, peripheral nerves and receptors that communicate messages quickly within the body
Learning goals
At the end of this section, I will be able to:
1. Describe the role of electrical impulses in the body’s responses to external stimuli.
2. Describe the role of hormones in the body’s responses to external stimuli.
The brain controls all bodily functions by communicating with different parts of the body, every second of every day. It does this in two ways: by sending electrical signals and neurotransmitters via the nervous system, and by communicating using chemical messengers (hormones) via the endocrine system.
The fundamental units of the nervous system are neurons (also spelled ‘neurones’) (see Figure 2.29).
A neuron is a single nerve cell that transmits signals between the brain and the body. Networks of neurons enable the communication of signals throughout the body, collectively making up the nervous system, which consists of up to one trillion neurons.
The human nervous system has two main parts:
• the central nervous system (CNS), which includes the brain and spinal cord
• the peripheral nervous system (PNS), which is all the neurons and nerve networks throughout the body that are outside the CNS.
Neurons transmit neural information to, from and within the central nervous system. There are three types of neurons (see Figure 2.30).
• Sensory neurons transmit neural information from sensory receptor sites in the PNS to the CNS. The sensory information being transmitted could be from any of your five senses.
• Interneurons (also called relay neurons) transmit neural information within the spinal cord and brain. Interneurons connect the sensory and motor neurons, and are only found in the CNS.
• Motor neurons transmit neural information from the CNS to the PNS, in order to initiate a response in an effector, which could be a muscle or a gland.
To help remember the three types of neurons, think of a SIM (Sensory, Inter, Motor) card from a mobile phone.
Figure 2.30 The three types of neurons – sensory, interneurons and motor – work together in a pathway called a reflex arc. Sensory neurons detect a stimulus, such as pain from touching a cactus, and send this information from the body to the central nervous system (CNS). Interneurons, found only in the brain and spinal cord, process this information and connect it to motor neurons. Motor neurons then carry messages from the CNS to muscles or glands to produce a response, such as pulling the hand away.
The key structures of a neuron are dendrites, cell body (soma), axon, myelin sheath, axon terminals and synapse. The synapse is not a true structure – it is the junction between neurons. The synapse consists of the axon terminal (of the sending neuron), the gap between the neurons (the synaptic cleft) and the dendrite (of the receiving neuron). Chemicals called neurotransmitters are released from a neuron on one side of the synapse and travel across the synapse to bind to the neuron on the other side. Figure 2.32 and Table 2.3 show the key structures of a neuron.
sensory neuron a nerve cell that transmits messages from sensory receptors to the central nervous system interneuron a nerve cell that transmits information within the brain and the spinal cord (central nervous system) motor neuron a nerve cell that transmits messages from the central nervous system to effectors (e.g. muscles or glands) synapse the junction between two neurons
Direction of impulse
Dendrite
Nucleus
Cell body (soma)
Axon
Myelin sheath (Schwann cell)
Direction of impulse
Axon terminal
Figure 2.32 The key structures of a motor neuron. The neural impulse travels in one direction only along the neuron, from the dendrites to the axon terminals.
Neuron structure
Axon
Function
Transfers electrical impulses from the cell body to the synapse. Axons are called 'nerves' when they are grouped together in a bundle.
Axon terminalLocated at the end of the axon, contains neurotransmitters that are held in vesicles. Neurotransmitters are released once an electrical impulse is received.
Cell body (soma)Contains most of the cell’s organelles, including the nucleus
Dendrite Contains receptor sites that receive neurotransmitters from neighbouring neurons
Myelin sheathA fatty, insulating layer made of Schwann cells that covers the axon. It helps keep the electrical signals inside the cell, allowing faster transmission.
Nucleus
Control centre of the cell; contains its genetic material
Schwann cellsSpecialised cells that form the myelin sheath
Synapse
Electrical messages are passed along the neuron, but neurons do not touch one another. There is a gap between the neurons, called a synapse. When an electrical impulse is received, the signal diffuses (travels) across the synapse in the form of chemical signals called neurotransmitters. The neurotransmitters then bind to the receptors on the dendrites of the neighbouring neurons.
Table 2.3 Neuron structures and their functions
1. Name the three types of neurons.
2. State the function of the myelin sheath that covers the axon.
3. Recall the role of interneurons.
Create a poster with models of two neurons, showing their structure and function. Make sure your poster has the following features: a title, a model of two adjacent neurons, labels for every structure on one of the neurons (along with a dot point explaining their function) and a label for the synapse.
You will need a piece of A3 paper, and your teacher will provide you with a selection of materials to make the model neurons. Suggestions include pipe cleaners, aluminium foil, pom-poms, drinking straws, modelling clay/plasticine or similar.
Suggested
1. Cut a pipe cleaner into three pieces. Wrap the pieces of pipe cleaner around a pom-pom. The pipe cleaner pieces will be the dendrites and the pom-pom will be the soma (the cell body of a neuron).
2. Wrap the end of another pipe cleaner around the soma, so you have a long piece coming down. This represents the axon.
3. Cut pieces of drinking straw about 2.5 centimetres (cm) long and thread them onto the axon. Leave gaps between the lengths of straw. You should have a bit of pipe cleaner left at the end. The straw represents the myelin sheath.
4. Take the end of the pipe cleaner near the bottom of the last myelin sheath, twist it into a loop and cut it so it splits – or add more small pipe cleaner pieces. You are beginning to make the axon terminals.
5. Repeat steps 1–4 for the next neuron.
6. Stick the neurons onto the sheet of paper and label the parts of one neuron with a dot point explaining the function of each structure (including the synapse).
7. Put up your posters in the classroom so that the axon terminals of one person's poster connect to the dendrites on the next poster. You should have a chain of neurons forming a nerve!
Communication along a neuron: Action potential
An action potential is another name for the electrical or neural impulse that moves along a neuron. Once the action potential reaches the axon terminal, neurotransmitters pass the action potential on to the next neuron.
When a neuron is not sending a neural impulse along its axon, it is ‘at rest’. Each neuron requires a minimum level of stimulation – called the neuron’s threshold potential – to activate an action potential. When enough neurotransmitters arrive from other neurons, and the threshold is reached, an action potential begins and moves along the axon like a wave. If the threshold is not reached, no action potential can start. This is known as the ‘all-or-none’ principle. Once an action potential has been triggered, it is self-sustaining; that is, it will continue to the end of the axon without further stimulation.
When neurons communicate with each other, the action potential travelling down the axon causes neurotransmitters to be released. Scientists have identified more than 100 types of neurotransmitters in the human brain alone, but evidence suggests there are significantly more than this. Some of the more common neurotransmitters are described in Table 2.4.
DopamineActs within the brain on pathways associated with motor functions (movement) and emotional arousal and motivation
AcetylcholineTransmits the message from the axon terminals of a motor neuron to a skeletal muscle
Serotonin Produced in the intestine and central nervous system; regulates appetite, mood, memory and behaviour
GlutamateA neurotransmitter in the CNS, involved with memory and learning
A lack of dopamine-producing cells in the brain can cause Parkinson’s disease, a neurological condition characterised by tremors, stiffness and uncoordinated movements.
Curare is a plant-based toxin that was used by South American Indigenous Peoples to paint the arrows of blow-darts. When shot at a victim, this toxin prevented acetylcholine from binding to the postsynaptic neuron, causing paralysis.
Some scientists theorise that low levels of serotonin are linked to depression.
High glutamate levels are involved with depression, anxiety and symptoms typical of attention deficit hyperactivity disorder (ADHD), such as the inability to concentrate. Low levels of glutamate are linked to insomnia, lack of concentration and low energy levels.
Table 2.4 Some common neurotransmitters and their roles
Neural impulse
Presynaptic neuron Postsynaptic neuron
The action potential reaches the presynaptic (axon) terminal.
This triggers the release of neurotransmitter from the synaptic vesicles in the presynaptic axon.
The neurotransmitter binds to receptors on the postsynaptic dendrite.
The action potential transmits through the next cell (postsynaptic neuron).
Figure 2.33 Communication between neurons. An action potential triggers the release of neurotransmitters from their synaptic vesicles in the presynaptic neuron. The neurotransmitters move across the gap and bind to receptors on the postsynaptic neuron.
Once the neurotransmitters are released, they bind to special receptor sites on the dendrite of the next neuron – called the postsynaptic neuron. The receptor sites convert the information back into electrical signals, which are then transmitted to the cell body of the postsynaptic neuron and along the axon. This process continues until the last neuron in the pathway connects to a muscle or a gland, causing a response.
Figure 2.34 An illustration of a synapse. (a) A synaptic vesicle in the axon terminal storing neurotransmitters, and the neurotransmitters (yellow) crossing the synapse to be received by the receptor sites (red) on the neighbouring neuron's dendrite. (b) Neurotransmitters (yellow) being released across the synaptic cleft and being received by the receptor sites (red) of the dendrite if they share the same distinct size and shape.
The sciatic nerve is the longest and widest nerve in the human body. It isn’t a single neuron, but a bundle of neurons, formed by a combination of five pairs of nerve roots in the lower spine. It extends from the lower back all the way to the tip of the toe and can be up to 1 metre long. The sciatic nerve is about 2 cm in diameter (roughly as thick as your thumb) and contains some of the longest individual neurons in the body. There are two sciatic nerves, one running down each leg.
1. State whether an action potential is a signal between two neurons, along a neuron or along an axon.
2. Recall what the ‘all-or-none’ principle means.
3. Define ‘neurotransmitter’.
4. Describe the role of the postsynaptic neuron.
5. Recall three common neurotransmitters and their function.
Drugs are substances that affect the brain by altering the way neurons send, receive and process information. Certain drugs, such as marijuana and heroin, imitate naturally occurring neurotransmitters to activate neurons. Alternatively, drugs such as cocaine and amphetamines stimulate neurons to produce more of the natural neurotransmitters, amplifying signals, blocking recycling of the chemicals, and disrupting communication channels.
WORKSHEET
Response time data analysis
A reflex action is a fast, automatic response that protects the body from harm. At times, the body must react quickly without waiting for instructions from the brain. During such instances, the spinal cord is mainly responsible for detecting the stimulus and initiating a response. A message is passed to the brain only after a brief delay, and the brain registers both the stimulus and the response after the reflex action has already taken place.
A reflex action, also known as a reflex arc, involves a maximum of three neurons. The signal travels to the spinal cord and then returns to the muscle, prompting a rapid contraction that does not involve the brain. Figure 2.36 shows an example of a reflex arc. When the brain is responsible for detecting and responding to a stimulus, the process is referred to as the stimulus–response model.
Figure 2.36 An example of a reflex arc. When you touch a prickly cactus with your finger, a receptor in a sensory neuron detects the pain and initiates an action potential. The impulse is carried to the spinal cord, where the sensory neuron connects to an interneuron. The interneuron then connects to a motor neuron, which sends an action potential through to the muscle tissue. Your muscles contract and you move your hand away.
How the nervous system drives response
A person sees a can of soft drink sitting on the bench. They feel quite thirsty, so they reach out and pick up the can to have a drink.
Referring to the components defined in the table below, describe how the person’s actions fit the stimulus–response model.
Part of the stimulus–response model
Stimulus
Definition of this part
Change in the environment
Receptors Detect the stimulus and stimulate the sensory neuron
Sensory neuronsTransmit an action potential (nerve impulse) to the integration area (the CNS)
CNS
Brain coordinates an appropriate response by sending nerve impulse along interneurons which connect to motor neurons
Motor neuronsTransmits an action potential (nerve impulse) to the effector organ (muscle or gland)
Effectors Act to cause the response
Response
Body’s reaction to the stimulus
Background information
Reaction time is a measure of how quickly a person responds to a stimulus. Many factors can affect reaction time, including age, gender, practice, blood sugar, alcohol, caffeine and general fitness. You will design your own investigation to explore the effect of practice time on reaction time.
Aim
To plan and investigate the effect of practice time on automatic reflexes and response times
Planning
1. Write a rationale on reaction times and the factors that affect this.
2. Create a relevant and specific research question for this practical.
3. Write a risk assessment for this practical.
Materials
• stopwatch
• ruler
• well-lit room
Method
Do not practise the experiment before starting to collect the results. You should start measuring immediately to ensure that you can determine the effect of practice time.
1. Have your partner lean their forearm on a bench with their weakest hand extending over the edge. If they are left-handed, they should use their right hand and vice versa. Ask them to make a pincer grip with their thumb and index finger with a gap of 2 cm between them.
2. Dangle the ruler above their hand so that the end marked 0 cm is hanging between their thumb and index finger.
3. Instruct them to catch the ruler with their thumb and index finger when they notice you have released it.
4. Release the ruler without warning.
5. Take note of the measurement on the ruler where they have caught it. This is the number of centimetres that the ruler fell before the person responded. Use the conversion table (see Table 2.5) to determine the reaction time.
6. Each person should complete the drop test 15 times. Record the ruler reading and reaction time for each test.
Results
Create a results table for this experiment.
Data processing
Draw a graph of drop test number against reaction time. Practical 2.1
Table 2.5 Conversion table for reaction times
Analysis
1. Identify any patterns, trends or relationships in your results.
2. The ruler drop experiment is not really testing a reflex. Draw a stimulus–response flow chart, highlighting the part that proves this is not a simple reflex. Explain why this is the case.
3. Compare your results with those of other people in your class. Do students who play particular sports or musical instruments have faster reaction times?
Evaluation
Limitations
1. Identify any potential sources of error in this experiment.
Improvements
2. Suggest any changes that could be made to the method to improve the quality of the data in future experiments. Justify your suggestions by explaining how each change will improve the data quality
Conclusion
1. Draw a conclusion from this experiment regarding practice time and reaction time. Justify your answer with data.
Quick check 2.6
1. ‘The brain is not immediately involved in a reflex arc.’ Propose whether this statement is true or false.
2. Illustrate a reflex arc for a person touching a flame.
3. Compare the reflex arc and stimulus–response models of the nervous system.
The nervous system does not work in isolation; it works with the body’s sense organs and the endocrine system. The endocrine system includes glands throughout the body that secrete hormones that regulate a variety of bodily processes, such as metabolism, digestion, blood pressure and growth.
Although the endocrine system is not directly linked to the nervous system, the two interact in many ways. Some of the most important endocrine glands are in the brain. These include the pineal gland, the hypothalamus and the pituitary gland.
Frontal lobe
Parietal lobe
Hypothalamus
Pituitary gland
Temporal lobe
Pons
Medulla
Spinal cord
Occipital lobe
Pineal gland
Cerebellum
Figure 2.37 A cross-sectional view of the brain, showing the location of the pineal gland, the pituitary gland and the hypothalamus
At the base of the forebrain is a tiny collection of neurons known as the hypothalamus (see Figure 2.37).
The hypothalamus links the nervous and endocrine systems. It is responsible for regulating several behaviours, such as sleep, hunger, thirst, sexual behaviour, and emotional and stress responses. The hypothalamus also controls the pituitary gland and the release of several hormones.
Other important glands in the body are the thyroid, thymus and adrenal glands, and the pancreas, ovaries and testes (see Figure 2.38). These glands are involved in regulating metabolism, fight-orflight responses and reproductive processes.
ENDOCRINE GLANDS
Pineal glandHypothalamus
Pituitary gland
endocrine system the system of glands that controls hormones in the body hormone a chemical messenger that is secreted by endocrine glands and circulates in the bloodstream to act on a target cell
Thyroid gland
Thymus gland
Adrenal glands
Pancreas
Testis
Ovary
Hormones are chemical messengers sent by the endocrine system to communicate with other parts of the body. They are produced by endocrine glands, which secrete the hormones directly into the circulatory or lymphatic system. The blood or lymph carries the hormones around the body, so the hormones are transported to, and have an effect in, a different part of the body from where they were made. The cells they affect are called target cells. Organisms are coordinated by many hormones, and small amounts of these chemicals can have major effects. Table 2.6 shows where some hormones are produced and what effect they have on the human body.
Table 2.6 Endocrine glands and the actions of the hormones they produce target cell a cell affected by a specific hormone
Hormone
Endocrine gland where produced
Action of hormone
Insulin Pancreas Reduces blood glucose levels by increasing glucose uptake by cells and promoting the conversion of excess glucose to glycogen in liver and muscle cells.
Glucagon Pancreas Increases blood glucose levels by stimulating the conversion of stored glycogen into glucose and releasing it into the bloodstream.
Adrenaline Adrenal gland Secreted during times of fear, stress or excitement, it increases heart rate, constricts blood vessels near the skin, dilates blood vessels to some muscles, raises blood pressure, and elevates blood sugar, preparing the body for physical action during the fight-or-flight response.
Erythropoietin Kidneys Promotes the production of red blood cells by the bone marrow.
Growth hormone (GH), antidiuretic hormone (ADH) and others
Pituitary gland GH promotes cell division, growth and repair in the body; ADH regulates the level of water in the blood.
Melatonin Pineal gland Regulates sleep patterns by inducing sleep. It is released in darkness and ceases to be produced in light.
Testosterone Testes Promotes bone growth, muscle development, facial hair growth, and deepening of the voice in males during puberty.
Oestrogen Ovaries Promotes breast and hair development and changes the shape of the hip bones in females during puberty.
Various thyroid hormones, including thyroxine
Parathyroid hormone
Thyroid
Parathyroid gland
Thymosin Thymus
Controls the body’s rate of energy production and metabolism and regulates the body’s sensitivity to other hormones.
Controls the amount of calcium in the blood and bones.
Stimulates the development of T cells, which are important in maintaining a healthy immune system.
What might be causing the increasing rates of cancer and metabolic conditions such as diabetes? What is the potential explanation for declining fertility rates? One hypothesis is that exposure to endocrine-disrupting chemicals is affecting our bodily functions. Although the scientific research supporting this hypothesis is mostly based on studies conducted on rats and mice, some researchers believe that it is applicable to humans as well. These chemicals are present in many household products including plastics. As a result, understanding safe levels of exposure is a topic of ongoing research.
1. Where might you find endocrine-disrupting chemicals in your house?
2. What everyday products might you find that contain BPA (bisphenol A)?
3. Discuss the stages of your life during which exposure to endocrine-disrupting hormones might be more har mful.
4. List some ways you could limit your exposure to endocrine-disrupting hormones.
1. Recall the part of the brain that is located at the base of the forebrain and controls many bodily functions, such as sleep, hunger and thirst.
2. Describe how hormones are transported around the body.
3. Define ‘target cells’.
Homeostasis is maintained by the endocrine and nervous systems working together. The nervous system plays the primary role in controlling and coordinating most actions of the human body. It works in partnership with the endocrine system, which produces particular hormones that are released into the bloodstream in response to external or internal changes.
The two systems work as a team by using chemical messengers and electrical impulses to communicate with cells and glands. The speed of message transmission and the length of the effects differ between the two systems: the nervous system provides fast-acting, short-lasting effects and the endocrine system triggers slow-acting, long-lasting effects.
The endocrine and nervous systems work in a coordinated way with all the other body systems to maintain a relatively stable internal environment and protect the body from harm.
2.39 An example of the nervous and endocrine systems working together is when you suddenly see a snake. The nervous system quickly processes the sight and sends signals to your muscles to jump back or run away. At the same time, the endocrine system releases adrenaline into your bloodstream, which raises your heart rate, increases your breathing and directs more blood to your muscles. This helps you react immediately and stay alert for longer.
Go online to access the interactive section review and more!
The key differences between the features of the endocrine and nervous systems are summarised in Table 2.7.
Feature
Signals
Pathway
Speed of information transfer
Duration of effect
Type of action and response
Target cells
Example of action
Nervous system
Electrochemical messengers (via electrical impulses and neurotransmitters)
Transmission by neurons in the nervous system
Fast
Short lived
Voluntary or involuntary
Localised cells
A friend throws a ball towards you. Your sensory receptors capture the visual stimulus, and through a network of neurons, the information is relayed to your brain. Subsequently, additional messages are conveyed through your spinal cord, and using motor neurons, your skeletal muscles receive stimulation, causing them to contract. As a result, you reach out and catch the ball.
Table 2.7 A comparison of the nervous and endocrine systems
Section 2.2 review
Online quiz
Section 2.2 questions
Remembering
Section questions
Endocrine system
Chemical messengers (hormones)
Transported in the bloodstream (circulatory system) and lymph (lymphatic system)
Slow
Typically longer lasting
Involuntary
Systemic (many cells may be affected)
When a male reaches puberty, the pituitary gland secretes a hormone called luteinising hormone. This acts on the testes and stimulates them to release testosterone. As the amount of testosterone builds up in his system, it triggers sperm production, muscle development, hair growth and changes to his voice.
Teachers can assign tasks and track results
1. Name two endocrine glands in the brain.
2. Recall how hormones reach their target cells.
3. State an example of a reflex action.
4. State the function of dendrites.
Understanding
5. Explain the difference in the speed of transmission within the nervous and endocrine systems.
6. Describe how an action potential is triggered and transmitted from one neuron to the next.
Applying
7. Construct a Venn diagram that shows the similarities and differences between the nervous and endocrine systems.
8. If a drug blocks receptor sites, explain the effect it could have on neurotransmission across synapses.
Analysing
9. Figure 2.40 shows how an impulse moving along an interneuron causes an impulse to be sent along another type of neuron, neuron X. Identify the name of neuron X.
X
Evaluating
10. The contraceptive pill contains a chemical that acts like the hormone oestrogen, and it must be taken daily by women. It is designed to stop sperm reaching an egg in several ways, including:
• suppressing ovulation, so an egg is not released from the ovaries
• making the cervical mucus thicker, so it is more difficult for sperm to reach the egg
• reducing the thickness of the lining of the womb, so it is not thick enough for an egg to attach to it.
Deduce some reasons why the pill is not guaranteed to work 100% of the time.
11. Imagine that you sneak up behind someone and make a sudden loud noise. They respond by blinking, twitching, moving their head suddenly, screaming or throwing their hands up. Using your knowledge of reflexes, discuss whether their response is voluntary, and give some reasons why this reflex might be a helpful mechanism to have.
12. Caffeine is known to increase alertness levels. You usually feel tired when the neurotransmitter adenosine is released. Discuss how caffeine may affect adenosine receptors.
13. Dopamine is a neurotransmitter that is involved in making us feel good. Caffeine works by slowing down the rate at which dopamine leaves the brain for your body, while at the same time not affecting the rate at which it is released into your brain. This leads to an increased level of dopamine in the brain for a short time. Deduce how this might affect your feelings and behaviour. Interneuron
tropism
directional growth of a plant in response to an external stimulus phototropism the growth of plants in response to light, where plant parts grow towards or away from light sources
auxin a plant hormone that regulates growth and development geotropism the growth of plant parts in response to gravity, with roots growing downwards and stems growing upwards hydrotropism the growth of plant roots towards areas with higher moisture levels
At the end of this section, I will be able to: 1. Describe how tropisms help plants respond to external stimuli.
Plants have evolved various ways to respond to changes in their environment to ensure survival and growth. These responses are known as tropisms, which are directional growth movements triggered by external stimuli. Tropisms help plants adapt to environmental factors such as light, gravity, touch and water, allowing them to thrive in a wide range of conditions.
Phototropism is the growth of plants in response to light. Plants need light for photosynthesis, the process by which they produce their food. To maximise light exposure, plants grow towards light sources. This growth is driven by auxins, plant hormones that accumulate on the shaded side of the plant, causing those cells to elongate. This uneven growth makes the plant bend towards the light, ensuring it can photosynthesise efficiently.
Geotropism (or gravitropism) is the growth of plant parts in response to gravity. Roots grow downwards into the soil to anchor the plant and absorb water and nutrients, while shoots grow upwards to access sunlight. This growth is also regulated by auxins, which accumulate on the lower side of the plant parts in response to gravity. In roots, auxins inhibit growth, causing them to grow downwards, while in stems, auxins promote growth, helping them grow upwards.
Hydrotropism is the growth of plant roots towards areas with higher moisture levels. Plants need water to photosynthesise and transport nutrients, so their roots grow in the direction of available water. This response ensures that plants can access sufficient water, especially in dry conditions. Roots detect moisture gradients in the soil, and are guided by them towards water sources, to maintain hydration and avoid drought stress.
Positive geotropism
Negative geotropism
2.42 Geotropism: roots grow downwards, stems grow upwards.
Thigmotropism is the growth response of plants to physical contact or touch. This is especially important for climbing plants, such as vines, which use this response to wrap around supports, such as trellises or fences. When plant tendrils or stems come into contact with an object, they begin to curl and grow towards it, securing the plant and enabling it to climb, for better access to sunlight.
Chemotropism is the growth of plants in response to chemicals in their environment. An example of chemotropism is the way pollen tubes grow towards the ovules during pollination, following chemical signals released by the flower’s ovary. Additionally, plant roots may grow towards or away from certain chemicals in the soil, such as nutrients or harmful substances. This allows plants to optimise their nutrient uptake and avoid harmful chemicals in their environment.
thigmotropism the growth of plants in response to physical touch or contact, such as vines wrapping around supports chemotropism the growth of plants in response to chemicals (e.g. pollen tubes growing towards ovules during pollination)
heliotropism the movement of plant parts in response to the direction of sunlight, effectively tracking the
as it
Heliotropism is the movement of plant parts, especially leaves or flowers, in response to the direction of the Sun. Unlike phototropism, which is a growth response to light, heliotropism involves the plant tracking the Sun’s movement across the sky. This helps maximise sunlight exposure throughout the day, enhancing photosynthesis. Some plants, such as sunflowers, are well known for their heliotropic behaviour, where their flowerheads follow the Sun from east to west.
Tropisms play a critical role in helping plants survive and thrive in their environments. Each type of tropism enables plants to optimise their growth and maximise their chances of survival. By growing towards light, plants can photosynthesise more efficiently; by responding to gravity, they can anchor their roots and ensure their stems grow upwards; by detecting water, they ensure they have enough hydration; and by responding to touch or chemicals, they can interact with their environment more effectively.
These adaptive responses allow plants to adjust to a variety of external factors, ensuring they remain healthy and can reproduce successfully. Without tropisms, plants would struggle to grow optimally, limiting their ability to survive in changing environments.
1. State the direction that plant roots grow in response to gravity.
2. Identify the type of external stimulus that triggers hydrotropism.
3. State the direction that plants move in response to sunlight during heliotropism.
Section 2.3 questions
Remembering
1. Define geotropism.
2. Recall the role that auxins play in tropisms.
Understanding
3. Explain the difference between phototropism and heliotropism.
Applying
4. Imagine that a plant is growing in a dark room with only one window. Describe how it would respond.
5. If a plant’s roots are in an area with excess moisture, describe what you would expect to happen.
Analysing
6. Determine how a plant’s survival would be impacted if it lacked the ability to respond with hydrotropism.
7. Examine a sunflower’s heliotropic behaviour and explain why this behaviour might be important for the plant’s growth.
Evaluating
8. Justify which tropism you think is most essential for plant survival.
Chapter checklist
Success criteria
Linked questions
2.1 I can describe organisms’ responses to external or internal stimuli.2, 6
2.1 I can describe the relationships between body systems that are necessary to coordinate a response to stimuli. 11, 12
2.1 I can describe how endotherms respond to changes in temperature.4, 5, 8, 15
2.1 I can describe how ectotherms respond to changes in temperature.4, 10, 15
2.2 I can describe the role of electrical impulses in the body’s responses to external stimuli. 1, 9, 13, 16, 17
2.2 I can describe the role of hormones in the body’s responses to external stimuli. 13
2.3 I can describe how tropisms help plants respond to external stimuli.3, 7, 14
Scorcher competition
Review questions
Remembering
Review questions
1. Name the key structures (A–F) of the neuron shown in Figure 2.47.
2. Define the term ‘homeostasis’.
3. Define hydrotropism and explain its importance for plant growth.
4. Name two examples of endotherms and two examples of ectotherms.
Understanding
5. Describe how a disorder in a feedback system can lead to hypothermia.
6. Explain how the process of regulation is monitored and adjusted by connections between the receptor, control centre and effector.
7. Explain how thigmotropism benefits climbing plants.
8. Describe how endotherms regulate their body temperature when exposed to cold environments.
Data questions
Go online to access the interactive chapter review
Applying
9. Sophia accidentally touches a hot pan and automatically snatches her hand away from it. Figure 2.48 shows the structures involved in this action.
Figure 2.48 Response to touching a hot pan
a) Identify and label the structures Figure 2.48.
Analysing
12. Categorise the following organs as receptor or effector.
a) hypothalamus
b) mechanoreceptor
c) liver
d) kidney tubules
e) pancreas
f) skeletal muscle
b) Contrast Sophia’s response to touching the hot pan to her using an oven-mitt to pick up the pan.
10. Imagine you are observing a reptile basking in the sun. Explain how this behaviour helps the reptile regulate its body temperature, comparing it to how an endothermic animal might respond to the same environmental conditions.
11. Summarise how the digestive, circulatory and respiratory systems interact with each other.
13. Compare the role of electrical impulses and hormones in the body’s responses to external stimuli.
14. Determine how a plant’s response to water availability (hydrotropism) would be affected if its auxin production was inhibited.
15. Categorise the following organisms as endotherm or ectotherm.
a) lizard
b) penguin
c) crocodile
d) polar bear
e) western dhufish
Evaluating
16. If a particular drug blocks the receptor sites on the dendrites of the postsynaptic neuron, propose how this may affect the neurotransmitters.
17. Taking the drug cocaine causes a build-up of dopamine in the synapse. Based on what you have read about dopamine, give your opinion on the statement, ‘I will just take it a couple of times; it won’t affect me’. In your response, discuss the effects that taking cocaine could have.
A student with diabetes measures their blood sugar level hourly. The data is plotted in blue in Figure 2.49. Another student, who does not have diabetes, also measures their blood sugar as a comparison, and this is plotted in orange. The students are careful to eat the same three meals on this day – breakfast, lunch and dinner at the same time. The student with diabetes injects insulin straight after each meal.
Student with diabetes
Student without diabetes
Blood sugar level (g/L)
Figure 2.49 Relative blood sugar level over 24 hours
1. Identify the homeostatic blood sugar level for each student.
2. Determine the times that the students ate breakfast, lunch and dinner.
3. Identify the peak blood sugar level for both students on this day.
4. Identify any patterns or trends that appear in the data.
5. Contrast the change in blood sugar level after each meal and provide a reason for the difference between the two students.
6. Infer a reason for the lower peak in blood sugar for the student with diabetes after eating lunch than after the other meals.
7. Justify whether the comparison of data would be valid if the students ate different meals on this day.
8. After the student with diabetes ate dinner, deduce the time that they injected insulin. Assume that insulin starts to act immediately upon injection.
9. Predict what would happen to the plotted data if the student with diabetes did not use insulin directly after the breakfast meal.
Texting is a common part of everyday life but using a mobile phone while doing other activities – especially driving – can be dangerous. When people divide their attention between tasks, their ability to respond quickly and make decisions can be affected. This is particularly important in situations that require fast reaction times, such as when operating a vehicle or machinery.
Research shows that even brief distractions, like checking a text message, can slow down your reaction time. This has serious consequences on the road. In Australia, strict laws are in place to prevent mobile phone use while driving. Drivers caught using a mobile device face a hefty fine and lose demerit points from their licence.
In this STEM activity, you’ll explore how texting affects reaction times by designing and carrying out an investigation.
Investigate whether texting is a distraction for people performing tasks.
In this activity, you will use materials and your imagination to create an experiment that produces:
• at least three sets of data
• at least three bar graphs
• a conclusion that clearly responds to the following scenario.
The Department of Transport is so concerned about young people’s attitudes towards texting while driving that it has hired your start-up company to conduct a sequence of experiments in the community to determine whether texting can slow down a person’s reaction times.
Suggested materials
• 30 cm ruler
• scissors
• cardboard
• paper
• pen
• mobile phone (to record slow-motion videos)
• presentation software (Microsoft PowerPoint, Google slides or Mac Keynote)
• video-editing software (for making short documentaries)
Research and feasibility
1. Research and make a list of the factors that influence a person’s reaction time.
2. Create a table and use it to list your predictions of how these factors will increase or decrease a person’s reaction time. A suggestion is given.
Factor Reaction time effect Reason
Being tired Increase reaction time moderately Tiredness decreases ability to absorb information
3. Discuss in your group, then list important information you will need to record about your participants (whose reaction times will be tested). Hint: Make sure you have thought about all the factors that might affect a person’s reaction times, such as sleep, exercise or playing video games.
Design and sustainability
4. Using the materials in the Suggested materials list, design a way to test the effect of mobile phone texting on a teenager’s reaction time.
5. Design a table that includes information about each participant’s recorded information.
6. Conduct your experiment, making sure you collect multiple sets of data for each participant and their important information.
and modify
7. Reflection is an integral and vital aspect of any project in the real world. How could you use ICT tools (e.g. apps, video, slow-motion camera) to enhance this experiment?
8. The results may change depending on the type of ruler used (e.g. metal, plastic or timber). Predict how the size or length of the ruler, and whether the dominant or non-dominant hand was used, might have affected the results.
9. Consider adding other distracting sounds and sights during the activity, such as turning on a TV set or flicking a flashlight on and off. Do participants’ responses slow with so many sensory signals?
Introduction
In every corner of the Earth, organisms have evolved remarkable ways to survive and thrive in their environments. These survival strategies, known as adaptations, are the result of millions of years of evolution. Plants and animals have developed structural, behavioural and physiological adaptations that help them meet the challenges posed by their surroundings, whether the intense heat of the desert, the cold of the polar regions or the nutrient-poor soils of mangrove forests. But survival is not just about how organisms adapt – it’s also about how they interact with and are influenced by their environment. Ecosystem health plays a crucial role in maintaining biodiversity and ensuring the survival of species. Abiotic factors such as temperature, water and soil conditions, along with biotic factors like competition and predation, all shape the delicate balance of ecosystems. By understanding how adaptations work and how we can monitor ecosystems, we can better appreciate the complexity of life on Earth and the importance of maintaining a healthy environment for future generations.
Adaptations allow organisms to survive in their specific environment.
Adaptations can be structural, behavioural or physical.
Vertebrate adaptations to:
• Desert ecosystems
• Polar ecosystems
• Marine ecosystems
Plant adaptations to:
• Desert ecosystems
• Mangrove ecosystems
• Bushfires
Population size and species diversity are impacted by a variety of factors.
Section 3.1
Section 3.2
Section 3.3
Biotic factors:
• Competition
• Predation
• Symbiosis
Abiotic factors:
• Temperature
• pH levels
• Nutrient levels
• Salinity
Ecosystems are monitored to track changes in natural and human-driven factors.
Sampling techniques:
• Quadrats
• Transects
• Capture-recapture
Human activity
Curriculum content
Biological sciences
Plants and animals have structural, behavioural and physiological adaptations that enable their survival in their environment
•
the
Population size and species diversity can be affected by abiotic and biotic factors; sampling techniques can be used to monitor abiotic factors and estimate numbers of organisms; ecological monitoring can be used to inform ecosystem health and impacts of human activity
• monitoring abiotic factors, such as temperature,
• effect of biotic factors, such as competition,
•
©School Curriculum and Standards Authority
Glossary terms
At the end of this section, I will be able to:
1. Describe structural, behavioural and physiological adaptations.
2. Describe adaptations that enable organisms to survive in specific environments.
Every organism on Earth has developed unique features that help it survive and thrive in its specific environment. These features, known as adaptations, allow organisms to cope with the various challenges they face in their habitats, whether extreme temperatures, lack of water or the presence of predators. From plants growing in the arid conditions of deserts to animals thriving in the icy cold of the poles, adaptations are key to the survival and success of life on Earth.
Plants, being immobile, must rely on their adaptations to survive the many challenges posed by their environment. Depending on the conditions of their habitat, plants have developed a range of strategies to cope with extremes in temperature, water availability and soil quality.
Desert ecosystems are characterised by extreme temperatures, low rainfall and arid conditions that make survival challenging. To withstand these harsh environments, desert plants have evolved specialised adaptations to conserve and store water. For example, the cactus stores water in its thick, fleshy stem, allowing it to survive for extended periods without rainfall. The surface of the cactus is covered with a thick waxy coating, which helps reduce water loss by evaporation. Similarly, many desert plants have small or needle-like leaves that minimise water loss and provide shade to the plant’s stem. Deep root systems enable these plants to access water deep underground, making the most of any infrequent rainfall.
Mangrove ecosystems are coastal habitats in tropical and subtropical regions, where saltwater and fresh water mix. These environments have fluctuating tides, high salinity and low oxygen levels in the soil, making survival a challenge for many species.
The roots of mangrove trees are adapted to filter out excess salt from the surrounding water. These trees also have aerial roots, which enables them to access oxygen, even when growing in water. Some species of mangroves can also expel excess salt through their leaves, ensuring the plant does not accumulate too much salt.
The plant’s red flowers bloom after rainfall, enabling the plant to reproduce quickly and efficiently in the brief periods when water is available.
adaptation a characteristic or behaviour that enhances an organism’s ability to survive and reproduce in its specific environment mangrove a wetland ecosystem of shrubs and trees growing in sheltered coastal areas where saltwater and fresh water mix
Bushfires are fast-moving, intense fires that occur in forests, grasslands and scrublands. They are often fuelled by dry vegetation and extreme weather conditions. In Australia, bushfires are a natural part of the environment, shaping ecosystems over thousands of years. They are driven by factors such as high temperatures, strong winds and low humidity, with some regions experiencing regular fire seasons. Many Australian plants have developed strategies that allow them to survive or regenerate after a fire. Some plants, such as Banksia and Eucalyptus, have thick, fire-resistant bark that protects their internal tissues from the heat. Certain plants, such as Grevillea and some Eucalyptus species, have seeds that require the heat from fire or smoke to germinate. This ensures that these plants can reproduce when the environment is right, after the fire has cleared the area of competing vegetation. Additionally, many plants in fire-prone regions are able to resprout quickly after a fire, with some regrowing from their underground root systems.
In 1995, Professor Kingsley Dixon and his team at Kings Park discovered that chemicals in smoke, not heat or ash, trigger germination in many Australian plants. After years of research, they isolated karrikinolide, named after the Noongar word ‘karrik’ (smoke), as the key molecule that breaks seed dormancy.
Figure 3.4 Banksia seeds are contained in woody cones. The heat of a fire causes the cones to open, allowing the seeds to fall to the ground and germinate in the nutrient-rich ash, a fertile environment for new growth.
This breakthrough has allowed rare species, such as Wilson’s grevillea, to be propagated for revegetation across Western Australia’s south-west. Artificial smoke, similar to liquid smoke used in food flavouring, is now being used to trigger germination in species that were once impossible to grow in nurseries.
There are multiple ways to replicate bushfire smoke for seed germination.
• Smoke water – a commercial product or homemade by bubbling smoke through water or soaking ashes in water. Seeds are soaked in this liquid to absorb the germination-triggering chemicals.
• Smoke-treated vermiculite – a soil additive infused with smoke chemicals that releases them gradually when watered.
• Smoke paper – a special type of paper that releases smoke chemicals as it degrades when placed over soil and watered.
• Direct smoking – seeds can be exposed to real smoke using controlled methods, such as smouldering native plant material in a kettle barbecue or cold-smoking them in a food smoker.
By using these methods, gardeners and conservationists can harness the power of smoke to improve germination and restore native plant populations safely and effectively.
1. State some adaptations of desert plants, such as cacti.
2. Identify the unique feature of mangrove trees that helps them survive in saltwater environments.
3. Explain how Australian plants regenerate after a bushfire.
Adaptations are special features that allow organisms to survive in their environment. These features develop randomly but give the organism an advantage over others of the same species, increasing their chances of survival and reproduction. Table 3.1 outlines the three types of adaptations.
Adaptation
Behavioural
Structural
Physiological
Description
Behavioural adaptations are actions or behaviours of organisms that increase their survival in a particular environment. For example, kangaroo rats in the desert are nocturnal (active at night), to avoid the daytime heat. Birds that migrate to warmer climates during winter have access to food and suitable living conditions.
Structural adaptations are physical features of an organism that improve its survival. These adaptations can be related to the organism's shape, size or specific body parts. For example, the thick fur of polar bears helps insulate them against the cold Arctic environment. Cacti have thick, fleshy stems that store water, and spines instead of leaves to reduce water loss. The webbed feet of ducks allow them to swim efficiently.
Physiological adaptations are internal processes that enhance an organism’s ability to survive and reproduce. These adaptations are often related to metabolism, reproduction and other bodily functions. For example, camels can tolerate extreme dehydration and can drink large amounts of water when it is available, storing it in their bodies for future use. Other physiological responses include sweating to regulate body temperature in hot conditions. Plants such as succulents can perform a special type of photosynthesis with minimal water, which allows them to thrive in arid environments.
Table 3.1 Types of adaptations
Vertebrates living in different ecosystems around the world face a wide range of challenges and they have developed a variety of behavioural, physiological and structural adaptations to help them survive. These adaptations allow them to cope with the specific conditions of their environments, such as extreme temperatures, scarce food resources or the need to move around in challenging terrain.
behavioural adaptations actions or behaviours that help an organism survive structural adaptations physical features of an organism that enhance its survival physiological adaptations internal processes that improve an organism’s survival
Australia is home to many unique organisms that have developed remarkable adaptations to survive in the diverse and often harsh environments of this country. Some of these adaptations are shown in Table 3.2.
Thorny devil
Kangaroo rat
• Has spines that help channel dew and rainwater directly to its mouth.
Koala
Acacia
• Camouflages itself among the desert sand and rocks to avoid predators.
• Has a specialised diet, feeding almost exclusively on ants, which it captures using its sticky, extendable tongue.
• To conserve water, it excretes highly concentrated urine and minimises water loss through its skin.
• Highly efficient kidneys produce very concentrated urine, minimising water loss.
• Obtains moisture from the seeds it eats, requiring almost no direct water intake.
• Produces dry faeces to conserve water.
• Long hind legs enable high, long jumps to escape predators.
• Large cheek pouches allow efficient food storage and transport.
• Nocturnal activity reduces water loss and exposure to predators.
• Burrow living provides a cooler, more humid environment, reducing dehydration.
• Specialised diet consisting almost exclusively of eucalyptus leaves.
• Has a long digestive tract to break down tough eucalyptus leaves and detoxify the plant’s toxic compounds.
• Mostly sedentary, to conserve energy due to the low-nutrient diet.
• Strong, sharp claws and opposable thumbs for climbing and gripping tree branches.
• Small, reduced or modified leaves to minimise water loss.
• Leaves are covered with a thick, waxy cuticle that reduces water loss.
• Extensive root system allows it to access water from deep underground sources.
• Many have thorns or spines that deter herbivores from eating them.
• Some shed their leaves during extreme drought conditions to reduce water loss.
Table 3.2 Some Australian species and their adaptations
Did you know? 3.1
Wombats are marsupials, in the mammal class. They have developed several adaptations that make them unique. Aside from having distinctively cube-shaped faeces, they have a sturdy rump that serves multiple purposes. It is used for defence, burrowing, bonding, mating, and potentially crushing the skulls of enemies against the burrow’s roof. However, the exact function of this behaviour is still under debate. The wombat’s rear end consists of four fused plates, surrounded by cartilage, fat, skin and fur. The animals use their backside to block their burrows, preventing predators from entering, and safeguarding their more vulnerable body parts. Wombats also have a pouch that faces in the opposite direction from the pouches of other marsupials, to protect their young from dirt when the mother is digging a burrow.
Desert environments are characterised by extreme temperatures, minimal water and limited food sources. Vertebrates in these environments must develop efficient ways to cope with the heat and conserve water.
Physiological adaptations
The centralian rough knob-tail gecko (Nephrurus amyae) has a low metabolic rate, which helps conserve energy and water. The gecko’s skin is also highly effective at retaining moisture, reducing water loss. The gecko is also nocturnal, foraging during cooler nights to avoid the intense heat of the day, and it can go for long periods without drinking, relying on the moisture from its food.
Behavioural adaptations
Many desert animals, such as the bilby, are nocturnal, meaning they are active at night when temperatures are cooler. By staying in burrows during the day, they avoid the searing heat and minimise water loss.
Structural adaptations
Other desert animals, such as hopping mice, have evolved large hind legs that allow them to cover long distances quickly and efficiently across the hot desert sand. Their fur-covered feet help protect them against the searing heat of the ground, while their long, thick tail provides balance as they hop. The mouse has also adapted to conserve water by being nocturnal, foraging at night when cooler temperatures reduce water loss, allowing it to thrive in the harsh Australian desert.
Adaptations to polar ecosystems
In polar regions, such as the Arctic and the Antarctic, extreme cold, ice and snow present significant survival challenges. Vertebrates that live in these environments have developed special adaptations to protect themselves from freezing temperatures.
Physiological adaptations
Penguins have a thick layer of blubber beneath their skin to insulate their bodies and keep them warm. Additionally, their metabolism is finely tuned to conserve energy and they can slow down their heart rates to survive extreme conditions.
Structural adaptations
Many cold-weather animals, such as polar bears, have dense fur that traps heat close to the body. White fur also serves as camouflage, helping them blend into the snowy environment and hunt for prey, such as seals. Penguins have compact, streamlined bodies that reduce heat loss and make them excellent swimmers, and their flippers are adapted for swimming rather than flying.
Behavioural adaptations
In harsh winters, some animals enter hibernation. This is a physiological state in which they lower their metabolic rate and survive on fat reserves until food becomes more abundant in the warmer months. Similarly, some animals demonstrate kleptothermy, a behaviour where they maintain warmth by sharing body heat with other animals. For example, some species may huddle together or share burrows to conserve energy and stay warm during the coldest months.
Organisms in Australian habitats have evolved many adaptations to thrive in their unique environments. The platypus has adapted to its semi-aquatic lifestyle by developing waterproof fur and webbed feet for efficient swimming and diving. It also uses electrolocation, which allows it to detect electrical signals produced by the movements of its prey in murky water, helping it to locate food even when visibility is poor. The sugar glider has adapted to life in the trees by developing a membrane of skin that allows it to glide between trees, conserving energy and avoiding ground predators. The echidna has adapted to its insectivorous diet by developing a long, sticky tongue to capture ants and termites from their nests, and the frill-necked lizard has a frill around its neck that it can flare up to appear larger and deter predators. This adaptation also helps it to regulate its body temperature. Your task is to investigate how organisms in an Australian habitat are adapted to their environment and then write a scientific report about your findings. Start by researching different Australian habitats and choose one to focus on, such as a rainforest or a desert. You should then research the organisms that are found there and how they are adapted to that environment. Write a scientific report summarising your findings, and share it with your classmates.
Marine ecosystems provide their own unique set of challenges, including saltwater, strong currents and the need for efficient swimming and oxygen management.
Structural adaptations
Fish and marine mammals have evolved streamlined bodies to reduce drag as they move through water. Dolphins and whales have flippers and tail flukes (two-lobed tails) that help them swim efficiently. These streamlined shapes allow them to travel at high speeds through the water and catch prey.
Physiological adaptations
Marine vertebrates, such as whales and seals, have specialised lungs and are able to store large amounts of oxygen in their blood. This allows them to hold their breath for long periods while diving to great depths in search of food. Sperm whales can dive to depths of over 2000 metres to find squid, holding their breath for up to 90 minutes.
Behavioural adaptations
Marine animals, such as sea turtles, migrate over long distances to find food or reproduce. These turtles navigate using the Earth’s magnetic field, and their long migrations ensure that they find suitable environments for nesting and feeding.
1. Explain why adaptations are important.
2. Distinguish between behavioural, structural and physiological adaptations.
3. Identify an example of a structural adaptation you might see in a polar ecosystem.
The loss of species can have profound effects on an ecosystem, because each species plays a specific role in maintaining the balance of nature. A key factor in determining a species’ ability to survive is its adaptations and its ability to cope in its environment. However, when environmental changes occur too rapidly, even the best-adapted species may struggle to survive, leading to extinction. Extinction, the permanent loss of a species, is a natural process that has occurred throughout Earth’s history. Extinctions can be categorised into several types, which are summarised in Table 3.3.
Description
Mass A significant proportion of Earth’s species are wiped out in a relatively short period, often due to a catastrophic event (e.g. asteroid impact, volcanic eruption, extreme climate change).
Example
The Cretaceous-Paleogene extinction, 66 million years ago, was caused by a massive asteroid impact in Yucatán, Mexico that wiped out 75% of all species.
FunctionalA species becomes so rare that it cannot play its ecological role effectively, or the population becomes too small to support a healthy and sustainable population. While some individuals may still exist, the species is effectively extinct.
The eastern quoll (Dasyurus viverrinus) was once widespread in south-eastern Australia, but its population numbers have declined significantly. Its numbers are so low that it no longer plays a significant ecological role. Table 3.3
Type of extinction Description
Small-scaleLocalised events often affect specific species or populations due to targeted threats, such as habitat loss, pollution, climate change or invasive species. Though smaller in scale, these extinctions can still disrupt local ecosystems and food webs.
The Bramble Cay melomys (Melomys rubicola) was endemic to Bramble Cay, a tiny coral island in the Torres Strait. It was the only mammal species native to the island and was well adapted to its sandy habitat. However, rising sea levels and increased frequency of extreme weather events due to climate change led to the loss of much of the melomys’s habitat. It was declared extinct in 2016, the first mammal species to be declared extinct due to climate change.
BackgroundThis is the standard rate of extinction that occurs naturally over time due to environmental changes, genetic factors and interactions with other species. It represents a baseline level of species loss against which other extinction events are measured.
Anthropogenic (human-led)
These extinctions are caused directly by human activities, including habitat destruction, overexploitation, pollution, introduction of invasive species and climate change. This type of extinction is concerning due to its accelerated rate and widespread impact.
On average, 10% of species are lost every million years, 30% every 10 million years and 65% every 100 million years.
The thylacine (Thylacinus cynocephalus) was once widespread in mainland Australia and Tasmania but it was hunted by European settlers. As a result, the thylacine’s population declined rapidly. The last known wild specimen was shot in Tasmania in 1930. Despite efforts to preserve the species in captivity, the last thylacine died in Hobart Zoo in 1936.
Table 3.3 (continued)
Try this 3.1
Complete some research to investigate factors that have led to a species becoming endangered or extinct. You should develop a presentation, such as a poster, video or report, describing the factors that led to the endangerment or extinction of your chosen animal.
In your class, go on a mock ‘field trip’, moving between your classmates’ presentations to learn the reasons for each of their animal’s endangerment or extinction. Once all data has been collected, work together as a class to explain why Australia has one of the world’s highest rates of species population decline and extinction.
1. Describe background extinction.
2. Name some causes of anthropogenic-driven extinctions.
3. At the end of the Permian era (250 million years ago), 96% of species became extinct due to intense volcanic activity in Siberia that caused global warming. Identify the type of extinction that occurred.
Section 3.1 review Online quiz
Section 3.1 questions
Remembering
1. Recall the definition of an adaptation.
2. Name the three types of adaptations.
Understanding
3. Describe how desert plants such as cacti conserve water.
4. Explain why mangrove trees have aerial roots.
5. Describe the five types of extinction: mass, functional, small-scale, background and anthropogenic.
Applying
6. Explain how the adaptations of a kangaroo rat help it survive in a desert environment.
Analysing
7. Compare the adaptations of desert plants and mangrove trees. How are their strategies for coping with environmental challenges similar or different?
Evaluating
8. Predict what might happen to species such Banksia or Eucalyptus if bushfires were less frequent in their environment.
9. Evaluate the consequences of human-induced (anthropogenic) extinction in Australia.
At the end of this section, I will be able to:
1. Explain how abiotic and biotic factors influence population size and species diversity.
Abiotic factors are the non-living elements that affect ecosystems. They include things like temperature, pH, water quality, nutrients and salinity. Changes in these factors can directly influence the ability of species to survive, reproduce and grow, thus affecting their population size and the diversity of species in an ecosystem.
• Temperature: Many organisms are adapted to specific temperature ranges. A rise in temperature can limit the survival of some species while allowing others to thrive. For example, if the temperature of a river increases due to climate change, it may reduce the oxygen level, making it difficult for cold-water fish species to survive. This would affect the population size of that species and possibly reduce the overall diversity of species in the ecosystem.
• pH levels: The pH of soil and water can affect the types of plants and animals that can survive in an ecosystem. A shift in pH, often caused by pollution, can make it difficult for certain species to thrive. For example, a more acidic environment can harm aquatic life, reducing population sizes and species diversity in aquatic ecosystems.
• Nutrient levels: The availability of essential nutrients such as nitrogen, phosphorus and potassium affects plant growth, which in turn affects herbivores and the predators that feed on them. For example, a nutrient-rich environment may encourage the growth of certain plant species, leading to an increase in herbivores that feed on them, which can affect the food web.
• Salinity: In coastal or mangrove ecosystems, the salinity of water plays a key role in determining which species survive. Species that thrive in fresh water may not survive in salty conditions, and vice versa. Changes in salinity, due to human activity or climate change, can drastically affect species populations and diversity in coastal areas.
Regularly monitoring these abiotic factors allows scientists to understand the current state of the environment and how it might be changing over time.
Making thinking visible 3.1
the 4Cs: nitrogen pollution
A study involving The University of Western Australia (UWA) has linked nitrogen pollution to changes in the distribution of European forest plants.
The research analysed 266 plant species over several decades. Surprisingly, many species moved westward rather than northward, as previously expected with rising temperatures. Thirty-nine per cent of species shifted west, while only 15% moved north. The study suggests that high nitrogen pollution from the atmosphere has allowed nitrogen-tolerant species –mainly from Eastern Europe – to spread rapidly, often displacing more specialised plants. These findings show that biodiversity changes are influenced by multiple environmental factors, not just climate change. Understanding these complex interactions is crucial for land managers and policymakers working to protect ecosystems.
Consider the following questions.
• Connections – How does this information relate to something you’ve learned before?
• Challenges – What is confusing or difficult to understand?
• Concepts – What are the key scientific ideas here?
• Changes – How does this information change the way you think about pollution and ecosystems?
The 4Cs thinking routine was developed by Project Zero, a research centre of the Harvard Graduate School of Education.
Try this 3.2
Abiotic and biotic factors play a significant role in influencing the distribution and health of native marsupial populations in Western Australia, particularly species like the ngilkat (Potorous gilberti), one of the world’s most endangered mammals.
Explore how the availability of food sources affects ngilkat populations. Consider factors such as:
• the types of food preferred by ngilkat
• seasonal variations in food availability
• the impact of habitat loss on food sources.
Examine the impact of climate on ngilkat populations. Focus on:
• the effects of extreme temperatures (hot and cold) on ngilkat health and behaviour, including the impact of bushfires
• changes in Australian climate patterns and their impact on habitats
• how ngilkat cope with temperature extremes (e.g. seeking shade, changing activity patterns).
Analyse the data you have collected to identify patterns and correlations between biotic and abiotic factors and ngilkat populations. You should prepare a presentation to share your findings with the class.
Aim
To observe and understand how ocean acidification affects the growth and health of marine organisms.
Time period
Approximately one week
Prior understanding
Ocean acidification is the ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of carbon dioxide from the atmosphere. Marine organisms such as corals, shellfish and plankton are sensitive to changes in pH levels.
Materials
• beakers × 2
• seawater
• pH meter or pH test strips
• vinegar (acetic acid)
• small pieces of coral (can be obtained from a pet store or aquarium supplier)
• shells (e.g. mussel/clam shells from a seafood market)
Method
1. Fill both beakers with seawater.
2. Add 5 mL vinegar (acetic acid) to one beaker to simulate ocean acidification.
3. Measure and record the initial pH of the seawater in each aquarium using the pH meter or test strips.
4. Carefully place the pieces of coral and shellfish into each beaker.
5. Leave the beakers for one week.
6. Note any visible effects of ocean acidification on the shells and coral.
Discussion
1. Analyse your data to determine the effects of ocean acidification on marine organisms.
2. Discuss the importance of reducing ocean acidification to protect marine life.
Conclusion
Draw conclusions about the impact of ocean acidification on marine ecosystems. Practical 3.1
Biotic factors are the living components of an ecosystem and their interactions with one another. These interactions can influence population size, species diversity and the overall structure of an ecosystem. Some of the key biotic factors that affect ecosystems are competition, predation, symbiosis and the impacts of human activity.
Monitoring ecosystems involves observing and measuring these biotic factors over time to understand how they influence ecological processes and biodiversity. By tracking changes in species populations, predator–prey dynamics or the effects of human intervention, scientists can assess the health of ecosystems and identify potential threats or areas that need conservation efforts.
Organisms often compete for limited resources such as food, space and mates. In ecosystems where resources are scarce, competition can lead to the decline of some species, while others may thrive. For example, invasive species that are more efficient at obtaining resources can outcompete native species, leading to a reduction in biodiversity. In plants, competition for sunlight and nutrients can limit growth, while in animals, competition for territory or food can lead to population shifts.
Figure 3.17 An example of competition is the struggle for resources between native plants and invasive Pinus species (e.g. the European pine). These pines are more efficient at accessing water and nutrients, which can lead to the decline of native species. Competition for resources (sunlight, water, soil nutrients) can inhibit the growth of native plants, reducing biodiversity. As the invasive species become more established, they often outcompete local plants and disrupt the natural balance of the ecosystem.
Predation is the relationship between predator and prey. A predator hunts and kills its prey for food, and this relationship can have a significant impact on the populations of both species. For example, the decline of a predator species due to habitat destruction or overhunting can lead to an increase in prey species. Conversely, an increase in the predator population can reduce the number of prey, which can alter the balance of the ecosystem.
Figure 3.18 An example of predation in Western Australia is the relationship between (a) the dingo and (b) the western grey kangaroo. Dingoes are apex predators that help regulate kangaroo populations. Where dingoes are scarce, due to human persecution or habitat loss, the kangaroo population can increase dramatically, leading to overgrazing and damage to vegetation. This alters the structure of the ecosystem, affecting the plant species that depend on the grazing balance for regeneration.
A symbiotic relationship is an interaction between two species that live together in close proximity, often in a long-term relationship. These interactions can be mutually beneficial, neutral or harmful to one or both parties involved. The three main types of symbiotic relationships are mutualism, commensalism and parasitism. Each plays a critical role in the stability and structure of ecosystems.
In a mutualistic relationship, both species benefit. An example of mutualism is the relationship between flowering plants and pollinators, such as bees. The plant benefits because the bee helps it reproduce by spreading pollen, while the bee benefits from the nectar it collects. Another example is the relationship between oxpeckers (birds) and large herbivores (e.g. buffalo). The oxpeckers eat ticks and parasites on the herbivores, benefiting from the food source, while the herbivores benefit from the removal of harmful parasites.
Figure 3.19 An example of mutualism. The acacia tree produces nectar that honey ants can eat. The ants protect the tree from herbivores (e.g. kangaroos) by stinging them. Both benefit: the acacia gains protection and the ants have a reliable food source.
In commensalism, one species benefits, while the other is neither helped nor harmed. For example, barnacles that attach to the shells of turtles benefit by being carried to new feeding grounds, but the turtle is not affected. Similarly, certain bird species, such as cattle egrets, follow herds of grazing animals. The birds benefit from eating insects disturbed by the movement of the herbivores, while the herbivores are largely unaffected by the birds’ presence.
In a parasitic relationship, one species benefits at the expense of the other. Parasites live on their hosts, often harming them in the process. An example of parasitism is the relationship between ticks and mammals. The tick benefits by feeding on the host’s blood, while the mammal suffers from blood loss and may also contract diseases transmitted by the parasite.
Figure 3.20 An example of commensalism. The honeyeater benefits from the nectar of the banksia flowers and uses the branches for shelter from predators. The banksia is largely unaffected by the birds.
Figure 3.21 The mistletoe plant, found in many Western Australian forests, is a parasite. It attaches to the branches of a host tree (e.g. eucalypts), and extracts water and nutrients. This can harm the tree by reducing its growth and reproductive success, especially if the tree is already stressed by environmental factors (e.g. drought).
1. Describe how competition between species can affect the populations of both species involved.
2. Explain how predation contributes to the balance of an ecosystem.
3. Give an example of mutualism and explain how both species benefit from the interaction.
Human activities such as deforestation, pollution, urbanisation and overfishing can drastically alter ecosystems. These activities can reduce habitat availability, pollute water sources, introduce invasive species and disrupt natural processes. For example, clearing forests for agriculture can destroy habitats for many species, leading to reduced biodiversity and changes in population dynamics.
Section 3.2 questions
Remembering
1. Name some of the main abiotic factors in an ecosystem.
2. Define predation and give an example.
Understanding
3. Explain how temperature can affect the distribution of species in an ecosystem.
4. Explain how humans are affecting ecosystems, giving an example.
Applying
5. Using the concept of symbiosis, explain how a bee pollinating a flower benefits both organisms.
Analysing
6. Identify the abiotic factors that could influence the health of a coral reef ecosystem.
Evaluating
7. Discuss how climate change could alter abiotic factors, and the resulting impact on species distribution.
At the end of this section, I will be able to:
1. Explain how ecological monitoring can be used to assess ecosystem health and the impacts of human activity.
2. Describe how sampling techniques can be used to monitor abiotic factors and estimate organism numbers in an ecosystem.
Ecosystem monitoring is the regular collection and analysis of data related to the environment, including the physical and biological components of an ecosystem. By monitoring these factors, scientists can track changes over time, identify potential threats to the ecosystem and make informed decisions about how to protect the environment.
Monitoring an ecosystem provides critical information about how the ecosystem is responding to changes in both natural and human-driven factors. These factors can include climate change, habitat destruction, pollution and over-exploitation of natural resources. Ecosystem monitoring also helps to ensure the sustainability of ecosystems, which is essential for the continued wellbeing of the species that rely on them, including humans.
Try this 3.3
You will work in teams to collaborate with local groups to monitor ecosystems and address environmental issues in your area.
Investigate ecosystem challenges in your local area, such as:
• changes in biodiversity (e.g. species decline or invasive species)
• pollution affecting waterways, soil or air quality
• habitat destruction due to urban development or climate change.
Identify organisations already working on ecosystem monitoring, such as the local council, Bushcare, Aboriginal Land Councils or national parks.
Contact one of these groups to learn more about specific issues and the work being done to address them. You may have an opportunity to be involved in conducting surveys, collecting samples or monitoring wildlife. Analyse the data collected or provided by the local groups and, within your team, propose some solutions to the issues identified. Consider factors such as feasibility, cost-effectiveness and potential impact.
Reflect on the experience of working with local groups and the impact of your proposed solutions. Consider the following questions:
1. How effective are current ecosystem monitoring efforts?
2. What further action can be taken to improve ecosystem health?
3. How can you continue contributing to environmental conservation in your community?
Figure 3.22 Western Australia’s forests, particularly jarrah forests, are experiencing widespread tree dieoffs, with large areas turning brown due to drought and climate change. This event, which is similar to coral bleaching, is affecting trees in shallow soils and regions where groundwater pumping has lowered the water table. Experts are calling for urgent action to implement a comprehensive monitoring system to track the health of these ecosystems.
1. Describe ecosystem monitoring.
2. State some factors that ecosystem monitoring can help track.
To monitor ecosystems effectively, scientists use a variety of methods to collect data. These techniques allow them to estimate the number of species present and track changes in the ecosystem over time. Sampling ecosystems involves selecting representative areas to observe and measure, enabling scientists to draw conclusions about the larger ecosystem without having to study every part of it.
3. Describe why monitoring ecosystems is important for humans. quadrat a square or rectangular frame used as a sampling tool to survey organisms in a section of an environment transect a straight line drawn across an ecosystem and used as a sampling tool to survey organisms
By carefully choosing sampling sites and using methods such as quadrats, transects or pitfall traps, researchers can gather valuable data on species abundance, diversity and the health of an ecosystem. This data helps inform conservation efforts, and aids scientists’ efforts to manage biodiversity and understand how ecosystems respond to environmental changes.
Quadrats are a sampling tool used by scientists to study the distribution and abundance of organisms in a specific area. Typically, a quadrat is a square or rectangular frame, usually made of wood or metal, that is placed on the ground to mark off a section of the environment. The size of the quadrat can vary depending on the type of organisms being studied and the nature of the habitat. In ecological studies, quadrats are commonly used to survey plants, because plants are stationary and easier to study in a set location.
3.23 An ecologist sampling with a quadrat
Scientists will place several quadrats in different parts of the study area, either randomly or along a transect, to get a representative sample of the organisms present. Once the quadrat is placed, researchers count the number of individual organisms, such as plants, or identify the different species within the quadrat. This is often done for plants and immobile organisms such as fungi or certain insects. The results from each quadrat can then be used to estimate the overall population size, diversity and distribution of organisms in the larger area.
By repeating this process in different quadrats, scientists can calculate averages and draw conclusions about the population structure in the study area. Quadrat sampling is an effective, non-invasive method that helps researchers gain insights into ecosystem health, biodiversity and environmental changes.
Worked example 3.1
Quadrat activity for estimating Australian species in bushland
Objective
To use quadrat sampling to estimate the number of a particular species in a section of Australian bushland.
Procedure
Step 1. Define the study area
Identify the area of bushland you want to study. For example, let’s say you are studying a 100 m × 100 m section of Australian bushland. This is a total study area of 10 000 m2.
Step 2. Select the sampling points
Use a random sampling method to choose a series of points within the study area. For example, you might randomly select five points for your quadrats. The coordinates for the selected points could be:
• Point 1: (10 m, 20 m)
• Point 2: (30 m, 40 m)
• Point 3: (50 m, 60 m)
• Point 4: (70 m, 80 m)
• Point 5: (90 m, 90 m)
Step 3. Place the quadrat at each sampling point
At each of the selected points, place a 1 m2 quadrat on the ground. This ensures consistency when recording data. Make sure the quadrat is placed flat, to capture all the organisms present within the frame.
Step 4. Record the species present
Within each quadrat, count the number of individuals of the species you are studying. For example, let’s say you are counting native grasses in the bushland. The data collected from each quadrat is as follows.
• Quadrat 1: 5 individuals of Themeda australis (kangaroo grass), 2 individuals of Poa australis (Australian bluegrass)
• Quadrat 2: 4 individuals of T. australis, 3 individuals of P. australis
• Quadrat 3: 6 individuals of T. australis
• Quadrat 4: 3 individuals of T. australis, 4 individuals of P. australis
• Quadrat 5: 5 individuals of T. australis, 1 individual of P. australis
continued …
Step 5. Calculate the average number of species per quadrat
Calculate the average number of individuals of each species, for all quadrats.
For T. australis (kangaroo grass), the total count is:
(5 + 4 + 6 + 3 + 5) = 23
Divide by the number of quadrats (5) to get the average number of T. australis per quadrat: 23
5 = 4.6 individuals per quadrat
For P. australis (Australian bluegrass), the total count is:
(2 + 3 + 0 + 4 + 1) = 10
Divide by 5 quadrats to get the average number of P. australis per quadrat:
10 ÷ 5 = 2 individuals per quadrat
Step 6. Estimate the total population or coverage
Estimate the total number of each species in the entire study area. The total study area is 10 000 m2, and each quadrat is 1 m2. Therefore, there are 10 000 quadrats in total.
For T. australis, multiply the average number of individuals per quadrat (4.6) by the total number of quadrats in the study area (10 000):
4.6 × 10 000 = 46 000 individuals
For P. australis, multiply the average number of individuals per quadrat (2) by 10 000:
2 × 10 000 = 20 000 individuals
Conclusion
By using quadrat sampling, we estimate that there are approximately 46 000 individuals of Themeda australis (kangaroo grass) and 20 000 individuals of Poa australis (Australian bluegrass) in the 100 m × 100 m section of bushland. This method allows researchers to estimate species populations over a large area without having to count every individual, providing valuable insights into species abundance and distribution.
A transect is a straight, often marked, line that is drawn across an ecosystem to provide a systematic way of studying how different environmental factors affect the distribution and abundance of organisms. Scientists use a transect by walking along this line and recording the types and numbers of plants, animals or other organisms they encounter at regular intervals. These intervals are typically predetermined and the observations are made at specific points along the transect, which allows consistent and reliable data collection.
Transects are particularly useful for studying ecosystems that change gradually over a distance, such as the transition from one habitat type to another, often referred to as an environmental gradient. For example, scientists might use a transect to study the shift in plant species from the edge of a riverbank to the interior of a forest. As they walk along the transect, they record the changes in plant types, soil conditions, moisture levels, light exposure or temperature, which may vary as the environment changes from one zone to the next.
By documenting the different organisms found along the transect, researchers can analyse how these changes in environmental factors influence biodiversity, plant growth and animal populations. This technique is especially valuable for studying how ecosystems respond to natural or humaninduced changes, such as climate change, land use or pollution. Transects help scientists understand spatial patterns in nature and gain insights into how ecosystems function and evolve over time. They are commonly used in ecology, conservation studies and habitat monitoring to assess the health of ecosystems and track the effects of environmental changes.
The capture–recapture method is commonly used to estimate the size of animal populations, especially mobile species. The procedure involves capturing a group of animals from the population, marking them in a way that does not harm them or affect their behaviour, and then releasing them back into the wild. The marking can be done by various methods, such as applying non-toxic paint, attaching tags, or even using specialised microchips for more accurate tracking.
After releasing the marked animals back into their habitat, scientists wait a certain period to allow the marked animals to mix back into the population. Subsequently, a second group of animals is captured, and the scientists count how many of the animals in this second capture are already marked from the first round. The proportion of marked animals in the second sample is assumed to be representative of the proportion of marked animals in the entire population.
Using a mathematical formula, the scientists can estimate the total population size of the species in the area. The most commonly used formula is the Lincoln-Petersen index, which provides a useful estimate of population size, especially for species that are difficult to count directly due to their mobility or elusive nature.
This method relies on certain assumptions. For instance, the population should be relatively closed, the marks should not affect the animals’ behaviour or chances of survival, and there should be no significant change in the population size between the two sampling events. Despite these limitations, the capture–recapture method is widely used in wildlife ecology and conservation biology.
Worked example 3.2
Researchers are studying the population of western ringtail possums (Pseudocheirus occidentalis) in a nature reserve in Western Australia. They aim to estimate the total population size using the capture–recapture method. The reserve is home to a number of these endangered marsupials and the researchers have set up an ongoing study to monitor their numbers.
Step 1. First capture (marking)
The researchers set out traps and capture 50 possums in the first round. They mark these possums with a small, non-toxic tag on their ear for identification. After marking, they are all released back into the wild.
• Number of possums captured and marked in the first round: 50
Step 2. Second capture (recapture)
A week later, the researchers conduct another round of trapping. This time, they capture 60 possums. Of these, 20 are found to be marked from the first capture, indicating they are recaptured individuals.
• Number of possums captured in the second round: 60
• Number of marked (recaptured) possums: 20
Step 3. Applying the capture–recapture formula
The capture–recapture method uses the Lincoln-Petersen index to estimate the total population size. The formula is: N = (M × C )
where:
• N = estimated total population size
• M = number of animals marked in the first capture (50)
• C = number of animals captured in the second round (60)
• R = number of marked animals recaptured (20)
Step 4. Calculation (estimated population size)
Substituting the values into the formula:
N = (50 × 60 ) = 3000 = 150 2020
Based on the capture–recapture data, the estimated population size of western ringtail possums in the reserve is 150.
Step 5. Interpretation
The researchers now have a population estimate of 150 western ringtail possums in the reserve. This estimate can help them assess the conservation needs of the species and determine whether additional protective measures are necessary. However, they must also consider factors such as migration, population changes and the assumption that marked possums have mixed randomly with unmarked individuals between captures.
Section 3.3 review
Online quiz
Go online to access the interactive section review and more! Section questions
Section 3.3 questions
Remembering
1. Name three sampling techniques used in ecosystem monitoring.
2. Describe the capture–recapture method used to estimate animal populations.
Understanding
3. Explain why it is important to monitor both abiotic and biotic factors in an ecosystem.
4. Explain why scientists might choose to use transects in an ecosystem study.
Applying
5. Researchers are studying the population of a rare species of frog in a wetland area. They use the capture–recapture method to estimate the population size. In the first round, they capture and mark 80 frogs. A week later, they capture 120 frogs, and find that 30 of these frogs are already marked from the first round. Using the Lincoln-Petersen formula, estimate the total population size of the frogs in the wetland.
Analysing
6. Analyse how the frequency and location of sampling points might affect the accuracy of ecosystem-monitoring data.
7. Compare the advantages and limitations of quadrat sampling versus capture–recapture methods.
Evaluating
8. Assess the potential consequences of ignoring abiotic factors in an ecosystem management plan.
9. Critique the capture–recapture method. What are some limitations or assumptions that could affect the accuracy of population estimates?
Chapter checklist
Success criteria
Linked questions
3.1I can describe structural, behavioural and physiological adaptations.2, 4
3.1I can describe adaptations that enable organisms to survive in specific environments. 4, 7
3.2I can explain how abiotic and biotic factors influence population size and species diversity. 10
3.3I can explain how ecological monitoring can be used to assess ecosystem health and the impacts of human activity. 6, 8, 12
3.3I can describe how sampling techniques can be used to monitor abiotic factors and estimate organism numbers in an ecosystem. 3, 5, 11
Scorcher competition
Reviewquestions
Remembering
1. Define extinction.
Review questions
Data questions
Go online to access the interactive chapter review
2. Name a physiological, behavioural and structural adaptation.
3. Name a common method used to estimate the population size of mobile animals.
Understanding
4. Explain the difference between structural, behavioural and physiological adaptations, and provide an example of each.
5. Explain how transects are used in ecosystem sampling, and why they are useful in studying environmental gradients.
6. Describe how monitoring data on species abundance can help researchers assess the health of an ecosystem.
7. Explain the relationship between adaptation and survival.
Applying
8. Explain how the data collected from monitoring ecosystems can be used to inform conservation efforts and biodiversity management.
9. If you were tasked with sampling an ecosystem to estimate the number of plant species in a forest, determine which sampling method (quadrats, transects or capture–recapture) you would choose and why.
Analysing
10. Compare the role of human activity versus natural disasters in causing species extinction. Which do you think has a greater impact on biodiversity in modern ecosystems?
Evaluating
11. Evaluate the effectiveness of using only one sampling technique (e.g. quadrats) compared with using multiple techniques (e.g. quadrats, transects, capture–recapture) when monitoring an ecosystem.
12. Discuss how monitoring programs in marine ecosystems, such as tracking coral bleaching, help to inform conservation efforts.
Quadrat sampling is a widely used method for studying ecosystems, particularly for assessing plant distribution and species diversity. By placing quadrats – square or rectangular frames –randomly or systematically within an area, scientists can collect data on species presence, abundance and coverage. This information helps them monitor changes in ecosystems over time and evaluate the impact of environmental factors, such as climate change, habitat destruction and pollution.
One important measure used in ecosystem monitoring is the Shannon diversity index (H´), which quantifies species diversity within a given area. The index considers species richness (the number of species present) and species evenness (how evenly individuals are distributed among species). A higher Shannon index value indicates greater biodiversity, suggesting a healthier and more stable ecosystem. Scientists use this index to compare different habitats, track biodiversity changes and assess ecosystem health.
By analysing quadrat data alongside measures such as the Shannon index, researchers can make informed decisions about conservation efforts and land management strategies.
Table 3.4 presents data collected from five quadrats, each covering an area of 10 m2
Researchers recorded the number of plant and animal species, total species count, biomass (g/m2), percentage of vegetation cover and Shannon diversity index for each quadrat.
Table 3.4 Quadrat sampling data showing species diversity, biomass and vegetation cover
1. Identify which quadrat has the highest species diversity.
2. Calculate the average total species count across all quadrats.
3. Calculate the average biomass across all quadrats.
4. Predict how the Shannon index would change if a quadrat experienced a 50% decrease in plant species count.
5. Using data from the table, identify the relationship between biomass and vegetation cover.
6. Deduce which quadrat is likely to experience the highest competition for resources and justify your answer.
Camouflage helps animals survive by blending into their environment or using patterns to confuse predators. Animals have evolved different camouflage strategies, including background matching (blending in), disruptive colouration (breaking up their outline) and mimicry (looking like another species).
Scientists and engineers use these principles to develop military camouflage, wildlife conservation techniques and even fashion designs.
Design and create a camouflaged animal model that can hide effectively in a chosen habitat. Your design should mimic real-world camouflage strategies to ensure survival.
1. Choose a habitat (e.g. forest, desert, ocean, snow-covered terrain).
2. Research real animals that live in that habitat and their camouflage strategies.
3. Sketch a design for a new species that blends into the chosen habitat.
4. Consider:
• colouration – will it match the background?
• pattern – will it use stripes, spots or disruptive markings?
• shape and texture – how will it avoid detection?
5. Construct a 3D model of your animal using materials such as paper, clay, fabric or paint.
6. Ensure it is well-adapted to ‘hide’ in a small diorama or background setting that represents its habitat.
• coloured paper, paint, fabric
• clay or recycled materials for the model
• natural materials (leaves, sand, twigs)
• timer for testing phase
7. Place your model in its habitat setting. Have another group try to find it within 30 seconds.
8. Discuss the following questions.
• How effective was the camouflage?
• How could the design be improved?
• What happens if the environment changes?
• How could this concept be used in military technology, conservation or fashion design?
1. Apply camouflage principles to technology. How do modern military uniforms and vehicles use camouflage?
2. Explore human impact. How does urbanisation affect animals that rely on camouflage?
3. Investigate counter-adaptations. How do predators evolve to see through camouflage?
Introduction
This chapter is all about atoms. The concept of the atom was developed by philosophers and scientists over thousands of years. Atoms of the same element can have different atomic masses, and some unstable atomic masses decay and emit radiation. Different types of radiation can be used for new technologies, including radiotherapy in medicine and radiography, and materials that use ionising radiation, such as smoke detectors.
Development of the atomic model
Democritus 460 BCE
Developed one of the first atomic theories of the universe
John Dalton 1803
Proposed that elements contain atoms
J.J. Thomson 1906
Proposed the ‘plum pudding’ model
Ernest Rutherford 1911
Proposed the nuclear model
Niels Bohr 1913
Proposed the electron shell model
Erwin Schrödinger 1926
Proposed the electron cloud model
James Chadwick 1932
Discovered the neutron
Section 4.1
Section 4.2
Section 4.3
Section 4.4
Everything is made up of atoms
Subatomic particles:
• Proton
• Neutron
• Electron
May undergo radioactive decay releasing
Current models:
• Planetary model
Periodic table of elements contains:
• Atomic number
• Mass number
Curriculum content
Chemical sciences
The atomic number and mass number of an element can be used to determine the number of protons, neutrons and electrons in an atom of the element; isotopes of an element have the same number of protons but different numbers of neutrons in their nuclei and have the same chemical properties
• determining the number of protons, neutrons and electrons in atoms of different elements
• exploring the isotopes of elements, such as hydrogen and oxygen
Collaborating and applying
Illustrate how proposed scientific responses to contemporary issues may impact on society
• exploring how Marie Curie’s discovery of new elements and work with radioisotopes contributed to the treatment of cancers
© School Curriculum and Standards Authority
Glossary terms
alpha particle atom
atomic number beta particle bioplastic
electron
electron shell electrostatic attraction gamma ray half-life ion isotopes mass number molecule neutron nucleus
nuclide notation octet rule proton radioactive decay relative atomic mass subatomic particle
At the end of this section, I will be able to:
1. Outline the different contributions to the development of the modern model of the atom.
The word ‘atom’ comes from the Greek word atomos, which means ‘indivisible’ or ‘un‑cuttable’. If you cut a platinum ring in half and then in half again, and continued to do this, you would eventually be left with an atom of platinum (Pt). Scientists have now provided evidence that there are particles even smaller than an atom, and that is something you will explore in this chapter.
An atom is the smallest possible form of an element, and there is a unique atom for every element. If a platinum atom was cut in half, it would not be platinum anymore, but would instead be two new elements.
Atoms are too small to be visible to the naked eye. A human hair is about as thick as 500 000 carbon atoms stacked end to end. Even with examples like this, it is almost impossible to truly understand the size of an atom.
You can only view an atom with a highly specialised microscope called a scanning tunnelling microscope (STM). The world’s first images of atoms were produced by a research team at the International Business Machines Corporation (IBM). In 1981, physicists Gerd Binnig and Heinrich Rohrer developed the first STM and they were awarded the Nobel Prize in Physics in 1986 for their efforts. This discovery allowed scientists to view images of many different atoms that had previously been unseen.
In 2013, researchers at IBM created the world’s smallest movie. They used carbon monoxide molecules and moved them by using the small tip of the scanning tunnelling microscope. The movie is called A Boy and His Atom – a boy meets an atom and they become friends. It was created using individual frames that were put together using stop-motion software. You can search for this film on the internet. Although it was constructed for fun, it shows just how far science has come in the study of atomic and molecular systems.
1. Define ‘atom’.
2. Recall the name of the microscope that allowed scientists to view atoms.
All elements are made up of one type of atom, and these atoms are identical to one another. They cannot be changed chemically into a different type of atom. All the known elements are arranged on the modern periodic table according to their atomic and chemical properties. They are represented by a symbol using one or two letters.
extend, challenge: element symbols
1. How do element symbols generally relate to their names in English?
2. Eleven element symbols do not match their English names. Can you identify all eleven elements?
3. Why is it important to know the origin of element symbols? How might this knowledge be important to a chemist?
The Connect, extend, challenge thinking routine was developed by Project Zero, a research centre at the Harvard Graduate School of Education.
Figure 4.4 Lead has the symbol Pb, from its Latin name plumbum. It was used in Roman plumbing pipes, hence its name.
Discussions about the atom and its structure for different elements have been going on within the scientific community for hundreds of years. In this section, you will examine the major discoveries that have contributed to our understanding of the atom and highlight how new experimental evidence can lead to a scientific model being updated or replaced. Concepts can be improved or completely changed as new scientific discoveries are made over time.
Democritus 460–370 bce
Democritus was the first philosopher to theorise about the atom. In the year 442 BCE, he hypothesised that if you take an object and cut it into smaller and smaller pieces, eventually you would reach a point where you could no longer cut it anymore. You would end up with a piece that was indivisible. Democritus called this piece atomos, which means ‘indivisible’ in Greek. He thought, for example, that water was made of water atoms and bread was made of bread atoms. This may sound silly now, but it was quite a sophisticated idea at the time, bearing in mind he had no modern technology such as microscopes to view these substances.
Aristotle 384–322 bce
Aristotle rejected the ideas of Democritus, instead believing that matter on Earth was made up of four elements – earth, air, fire and water – and the amounts of these elements determined how materials behaved. Aristotle had such an influence over people at the time that it took about 2000 years for Democritus’s theory to be re‑examined.
John Dalton 1766–1844
4.5
The Greek philosopher Democritus theorised about the atom.
WORKSHEET
The development of the atomic model
Figure 4.6
The Greek philosopher Aristotle proposed that all matter was made up four elements: earth, air, fire and water.
Dalton is credited with initiating research into modern atomic theory in 1803, more than 2000 years after Democritus first proposed his ideas on the atom. Dalton suggested that all elements, which were now arranged in the periodic table, contained atoms, and that atoms of the same element were identical in size, shape and mass. This theory was called the ‘solid sphere model’ because Dalton believed the atom was a solid sphere. The question he could not answer was why atoms behaved the way they do.
Figure 4.7
John Dalton was an English chemist, physicist and meteorologist. He is best known for initiating research into modern atomic theory.
WORKSHEET The gold foil experiment
alpha particle a positively charged particle that is emitted from the nucleus of some radioactive elements during radioactive decay (disintegration) of an unstable atom nucleus the central part of the atom, containing its protons and neutrons; plural nuclei
Thomson was the first scientist to discover particles smaller than the atom, disproving Dalton’s and Democritus’s theories. Surprisingly, the first subatomic particle to be discovered was the lightest – the electron – and in 1906 Thomson won a Nobel Prize for his work. By studying ‘rays’ in a cathode ray tube, Thomson was able to determine that these ‘rays’ had a mass much lighter than a hydrogen atom, the lightest particle known to science at the time. He therefore concluded that these ‘rays’ were not rays at all, but very light particles. These particles were also attracted to a positively charged metal plate, indicating that they were likely to be negatively charged. He named these particles ‘corpuscles’, but they are now called electrons.
Figure 4.8 Thomson proposed the plum pudding model and is credited with discovering the electron.
Negative ‘plums’ or electrons
Sea of positive ‘pudding’
Figure 4.9 The plum pudding model consists of negative electrons (plums) scattered through a sea of positive charge (pudding).
The first model of the structure of the atom was proposed by Thomson, who named it the ‘plum pudding’ model (see Figure 4.9). Thomson knew that electrons were negatively charged and that atoms were neutral, so he theorised that there must also be positive charge within the atom that equalled the negative charge of its electrons. He imagined the atom as negatively charged electrons (plums) embedded in a positively charged ‘pudding’.
In 1911, Ernest Rutherford and colleagues Hans Geiger and Ernest Marsden fired alpha particles (helium nuclei) at a thin piece of gold foil, in the famous gold foil experiment.
Rutherford predicted that if the atom was like Thomson’s plum pudding model, then all the alpha particles should pass straight through the atom undisturbed. This is not what happened! It was true that almost all (99.99%) of the alpha particles passed straight through the foil and were detected at the other side, indicating that the atom was mainly empty space. However, surprisingly, some of the alpha particles bounced back or were deflected, as if they had hit something (see Figure 4.11). Rutherford concluded that there must be an area of charge, concentrated in the middle of the atom, with enough mass to cause the alpha particles to deflect or bounce back, thus disproving the plum pudding model.
Figure 4.10 Rutherford stated that there was a large concentration of charge and mass in the centre of the atom and that most of the atom was empty space.
In analysing the results of this experiment, Rutherford devised his own model of the atom. In this model, there is a charged area with substantial mass concentrated in the middle of the atom, called the nucleus (see Figure 4.12b). Rutherford and many other scientists assumed the nucleus to be positively charged because it repelled the positively charged alpha particles that were fired towards it. Rutherford concluded that the negative electrons orbited this central region. Rutherford’s model is often called the ‘nuclear’ model of the atom. Although many other scientists contributed to the developing knowledge at the time, it was Rutherford who named the positively charged particles in the nucleus ‘protons’.
Radioactive source
Alpha particles Detector
A: Moderate deflection
B: Passed straight through
C: Large deflection
D: Bounced back
Figure 4.11 The gold foil experiment conducted by Rutherford and colleagues proved that most of the atom was empty space and that there was an area of charge and mass concentrated in the middle of the atom.
1. Recall the four elements that Aristotle believed made up all matter on Earth.
2. State the name of the subatomic particle that Thomson discovered and the name of his atomic model.
3. Use the word list to complete the sentences below.
alpha
empty space
plum pudding model nucleus passed through
Rutherford conducted the gold foil experiment, firing ____________ particles at a thin piece of gold foil. Most of the alpha particles ____________; however, a small number were deflected back. Rutherford hypothesised that the reason for this was that the alpha particles either passed through a region of ____________ or hit a central region of concentrated mass and positive charge, which he called the ____________, disproving the ____________.
Aim
To investigate the three-dimensional structure of molecules.
Materials
• 100 mL propan-2-ol
Method
• 250 mL beaker
1. Draw the results table shown in the Results section.
• 100 mL measuring cylinder
2. Predict what will happen to the total volume when 100 mL of alcohol is added to 100 mL of water. Propose what the total volume of the solution will be.
3. Use the measuring cylinder to measure 100 mL of water and pour it into the beaker.
4. Using the same measuring cylinder, measure 100 mL of propan-2-ol and pour it into the beaker containing the water.
5. Note the actual total volume when the two solutions are mixed together.
Results
Copy and complete the following table.
Table showing predicted and actual volume of water and alcohol
Predicted volume with 100 mL of water and 100 mL of alcohol
Actual volume with 100 mL of water and 100 mL of alcohol
Discussion
1. Discuss whether the actual final volume differed from your prediction, and if so, why this was the case.
In 1923, physicist Robert Andrews Millikan won the Nobel Prize in Physics for his now famous oil drop experiment, which provided evidence for the negative charge of the electron.
Use the internet to answer the following questions.
1. What is the Millikan oil drop experiment?
2. How does the experiment provide evidence of the negative charge of the electron?
Millikan’s evidence was consistent with evidence from earlier discoveries, including Thomson’s discovery of the electron and Rutherford’s hypothesis that electrons exist in space around a dense positively charged nucleus. These three key findings were pivotal for the consolidation of knowledge about electricity – the movement of negatively charged electrons through a substance.
By the early twentieth century, scientists had a good idea about atomic structure; they just needed to identify where the electrons were actually situated in the atom.
Niels Bohr proposed his model of the atom (a modification of Rutherford’s theory) in 1913 after observing the behaviour of electrons. Bohr was trying to compare the behaviour of electrons and the behaviour of light. He said electrons moved in fixed circular orbits around the nucleus in structures called shells, and that these shells were specific distances away from the nucleus and were the same for all atoms of a particular element. Bohr’s model is often called the ‘planetary model’ because it resembles how planets orbit a central star.
Electrons located in shells that were further away from the nucleus had higher energies than those closer to it. Bohr stated that when electrons absorb energy, or get excited, they jump to the next energy level or shell. When they fall back to their original level, they emit some light, which matches the amount of absorbed energy.
Scientists now know that Bohr’s model has some flaws, but it provided some important understanding about the behaviour of electrons. Perhaps more importantly, it is the model that you will recognise and use most in your studies.
Figure 4.14 Bohr proposed that electrons were not spread randomly through the atom but were arranged in discrete energy levels or shells.
Although Bohr’s model proposed that electrons exist in ‘shells’ around the nucleus, scientists knew very little about the position and behaviour of the electrons in the ‘shells’. Erwin Schrödinger stated that it is impossible to predict where a specific electron will be situated in the atom at any given time. The only thing you can predict is where in the atom you are most likely to find an electron. This contradicted Bohr’s idea of electrons being in fixed shells around a central nucleus. Schrödinger proposed the electron cloud model, which shows the locations in the atom with the greatest probability of containing an electron. This relates to the wave properties of the electron (quantum, or wave, mechanics).
4.15 Bohr’s model of the atom is sometimes called the planetary model. It shows electrons in fixed shells around a central nucleus.
Figure 4.16 Schrödinger proposed the electron cloud model, contradicting Bohr’s model of fixed electron shells.
4.17 The electron cloud model of a boron atom
4.18 Chadwick discovered the neutron, the last subatomic particle to be discovered. This completed the atomic model in use today.
There is one subatomic particle that was yet to be discussed. The neutron was the last of the three subatomic particles to be discovered. Because a neutron has no charge and does not repel the protons in the nucleus, it was relatively undetectable. This was the case until James Chadwick started working with beryllium atoms and alpha particles in 1932. When he collided these two particles, an unknown radiation made up of neutrally charged particles was released. He named these particles neutrons. Often in high school, we use the Bohr model (protons in the nucleus) and shells of electrons, but we also include neutrons in the nucleus in our diagrams.
4.19 We use the Bohr model, also showing neutrons, because it is a simplification of the electron cloud model.
1. a) Recall the name Bohr gave to the structures that contained electrons.
b) Describe how Bohr's explanation of these structures differed from Rutherford’s model.
2. Identify the subatomic particle that Chadwick discovered.
The evolution of the atomic model is an excellent example of how individual scientists contributed to and continue to revise our understanding of atomic structure. However, it is important to note that this is still a model and there may be new discoveries to come! After all, at one time scientists thought that the plum pudding model was the correct model of atomic structure. It is important that scientists continue to ask questions, conduct experiments and critique other people’s work to increase our understanding of atomic structure. Figure 4.20 summarises the development of the modern atomic model.
J.J. Thomson 1906
Discovered the electron and proposed the plum pudding model
John Dalton 1803
Elements and compounds contain atoms
Gold foil experiment supported the existence of the nucleus
Discovered the neutron
Erwin Schrödinger 1926
Electron cloud model; electrons are not in fixed shells
The ‘Matilda effect’ refers to the systematic denial or minimisation of women’s scientific contributions, with their work often attributed to male colleagues. This phenomenon has led to the historical erasure of many women scientists’ achievements, perpetuating gender bias in the recognition and rewarding of scientific work.
The following examples underscore the challenges women have faced in the scientific community. Throughout the development of atomic theory, numerous women made significant contributions that were often overlooked, marginalised or attributed to their male counterparts, due to systemic misogyny.
Marie Curie’s pioneering work in radioactivity was foundational to our understanding of atomic structure. She discovered the elements polonium and radium, and coined the term ‘radioactivity’. Despite her monumental contribution, she faced substantial gender based discrimination. In 1903, when the Royal Institution in London invited the Curies to speak on radioactivity, only her husband, Pierre Curie, was permitted to speak.
An Austrian Swedish physicist, Lise Meitner played a crucial role in the discovery of nuclear fission, the process that powers nuclear reactors and atomic bombs. Despite her significant contribution, it was her collaborator, Otto Hahn, who received the Nobel Prize in Chemistry in 1944 for this discovery. Meitner’s role was largely overlooked, exemplifying the systemic bias that led to the erasure of women’s contributions in science.
A Canadian American applied mathematician and computer scientist, Charlotte Froese Fischer developed the multi configurational Hartree Fock (MCHF) approach to atomic structure calculations. Her theoretical prediction of the existence of the negative ion of calcium was experimentally confirmed, marking the first known anion of a Group 2 element. Despite her significant contribution, she faced challenges in a male dominated field, reflecting the broader systemic issues that often led to the under representation and undervaluation of women’s work in science.
Did you know? 4.1
In this section, you have learned that the atom is made up of three types of subatomic particles. However, there are actually a few more. Another subatomic particle is the neutrino, which is hypothesised to act like an electron but have a neutral charge. Neutrinos don’t exist in an atom but are produced when two or more atoms fuse together under extremely high temperature and pressure, such as the conditions on the Sun. Neutrinos are then emitted and travel through space, some reaching Earth. In 2015, Professors Takaaki Kajita and Arthur B. McDonald were awarded the Nobel Prize in Physics for their work, which provided evidence that neutrinos have mass, just like electrons.
Professor Janet Conrad is an American physicist and a leading expert on neutrinos. She has played a key role in the Main Injector Neutrino Oscillation Search (MINOS) experiment, which was designed to study the behaviour of neutrinos as they travelled through Earth. She led a team that developed the software and algorithms used to analyse the data collected by the experiment. The MINOS experiment provided important evidence for the phenomenon of neutrino oscillation, which is the process by which neutrinos change their identity as they travel.
Professor Conrad has been involved in the MicroBooNE experiment, which is designed to study low-energy neutrinos. Her work on this experiment has focused on measuring the properties of neutrinos and improving our understanding of their interactions with matter. This research has important implications for a wide range of fields, from particle physics to astrophysics.
Section 4.1 review
Online quiz
Section 4.1 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Recall what the Greek word atomos means in English. How does this relate to the word ‘atom’?
2. Recall who discovered the neutron.
Understanding
3. Summarise what Rutherford predicted would happen, according to Thomson’s plum pudding model, when he fired alpha particles at gold foil.
4. Identify why some alpha particles bounced back towards the detector in Rutherford’s gold foil experiment.
Applying
5. Compare Rutherford’s model of the atom with the plum pudding model.
Analysing
6. Analyse the differences between Schrödinger’s and Bohr’s models of the atom.
Evaluating
7. Discuss the evidence that led to Rutherford concluding that most of the mass and all the positive charge of the atom were concentrated in the centre.
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WORKSHEET
The structure of the atom
Learning goal
At the end of this section, I will be able to:
1. Compare the relative mass and charge of protons, neutrons and electrons.
You have already learned that the word ‘atom’ comes from the Greek word atomos, meaning ‘indivisible’.
subatomic particle one of the particles that make up an atom
proton a subatomic particle with a positive charge found in the nucleus of an atom
neutron a subatomic particle with a neutral charge found in the nucleus of an atom electron a subatomic particle with a negative charge found outside the nucleus of an atom
As new technologies developed, physicists discovered that the atom is actually made up of three main types of subatomic particles: protons, neutrons and electrons. There are different numbers of these subatomic particles in each element, which will be discussed in more detail later in this chapter.
Did you know? 4.2
ordinary hydrogen: an unusual element
Hydrogen is the only element that does not contain all three subatomic particles. Most hydrogen atoms only contain one proton and one electron. It is missing a neutron!
Since 2008, physicists have learned a lot more about particles within atoms from studies using the CERN’s Large Hadron Collider (LHC). Here, subatomic particles are smashed together at close to the speed of light. The remains are then analysed. When the LHC was first developed, some scientists believed it would create many miniature black holes that might even swallow the Earth. Luckily, despite being the world’s biggest machine, the LHC currently cannot produce enough energy for this to occur.
Scientists once thought the atom was the smallest particle that existed. You know that protons, neutrons and electrons make up the atom, but is there anything that makes up these subatomic particles? Because an electron has wavelike properties, it is difficult to define it or measure its size. Some quantum physicists think that an electron could even be in two places at one time.
The particles that make up protons, neutrons and electrons are known as quarks. Do some research on quarks. What are their different names? What is known about them?
Even with the most powerful microscopes, scientists cannot see inside an atom, so they create models of the atom to represent ideas that cannot be observed. To help visualise the structure of an atom, you can model it as a mini solar system. In the middle of our solar system is the Sun, and orbiting the Sun are the planets, with most of the rest of the solar system being empty space.
The atom has a similar structure. In the middle of the atom is a structure called the nucleus, where the protons and neutrons are situated. Orbiting the nucleus in shells or orbitals are the electrons. The shells are drawn as circles and are at different energy levels depending on how far from the nucleus they are.
Just like the solar system, most of the atom is empty space. To give you an idea of how empty an atom is, if an atom was the size of Optus Stadium in Perth, then the nucleus would be the size of a cricket ball in the middle of it!
electron shell
an area around the nucleus of an atom where electrons orbit
octet rule
electron shells fill sequentially with 2,8,8,2 electrons
electrostatic attraction
a force pulling together oppositely charged particles
Electrons orbit the nucleus of an atom in shells, but because they are negatively charged, they repel one another. As a result, there is a limit to the number of electrons that will orbit in each electron shell. The number of electrons in each shell is represented by an atom’s electron configuration, and it can be complicated. However, the rules are reliable for the first 20 electrons that fill up the shells. Electrons fill the shells sequentially – that is, they fill the first shell (closest to the nucleus) with 2 electrons, then the second shell with 8 electrons, then the third shell with 8 electrons, and then the fourth shell with 2 electrons. You can remember this as the 2,8,8,2 rule, or the octet rule. For example, oxygen (O) has 8 electrons, with an electron configuration of 2,6.
you know? 4.3
Maria Goeppert Mayer was a pioneering physicist whose work on the nuclear shell model revolutionised our understanding of the behaviour of subatomic particles. Born in Germany in 1906, Goeppert Mayer moved to the United States in the 1930s and began working on the physics of the atomic nucleus. Her research on the behaviour of protons and neutrons led to the development of the nuclear shell model, which explained the stability and behaviour of atomic nuclei based on the arrangement of their protons and neutrons.
Figure 4.27 Goeppert Mayer's ground-breaking work on the nuclear shell model earned her the Nobel Prize in Physics in 1963, making her only the second woman to receive this honour after Marie Curie. Quick check 4.4
1. Name the structure at the centre of the atom and what it contains.
2. Identify where the electrons are located.
To understand more about atoms and how they behave, you need to know more about the three subatomic particles within them.
If electrons are whizzing around at enormous speeds inside the atom, why don’t they just fly off into space? The reason they remain has to do with the electrical charges of the subatomic particles. Remember, each of the protons in the nucleus in the middle of the atom has a positive charge (+1) and each electron orbiting the nucleus has a negative charge (–1). Positive and negative charges follow two basic rules of electrostatics: opposite charges attract and like (the same) charges repel. This means that the protons and electrons in an atom interact with each other (electrostatic attraction), and this stops the electrons from flying off into space. Table 4.1 summarises the relative charges of the subatomic particles.
Mass
Protons and neutrons have very similar masses: a proton has a mass of 1.673 × 10–24 grams (g) and a neutron has a mass of 1.675 × 10–24 g. These numbers are very small and almost the same, so for practical reasons, protons and neutrons are assigned a relative mass of 1 atomic mass unit (amu). These values are much easier to remember and work with. Electrons have a relative mass much smaller than a proton or a neutron. Table 4.2 summarises the relative masses of the subatomic particles.
Subatomic particleRelative charge
Proton +1 (positive)
Neutron 0 (neutral)
Electron –1 (negative)
Table 4.1 The relative charges of the three types of subatomic particles
Quick check 4.5
Subatomic particleRelative mass
Proton 1
Neutron 1
Electron 1/1836
Table 4.2 The relative masses of the three types of subatomic particles
1. Copy and complete this table to summarise the differences in charge and relative mass of the three subatomic particles.
Subatomic particleSymbolLocationRelative chargeRelative mass
Proton p+
Neutron n0
Electron e–
Section 4.2 review
Online quiz
Section 4.2 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Name the three types of subatomic particles that make up the atom.
2. Identify which subatomic particle has the smallest mass.
3. Recall the name of the structure at the centre of an atom where the protons and neutrons are located.
Understanding
4. Write the electron configuration for a neon atom that has 10 electrons.
5. Draw a labelled diagram that illustrates the Bohr (or planetary) model of a beryllium atom that contains 4 protons, 5 neutrons and 4 electrons.
Applying
6. Draw a diagram that illustrates the electron cloud model of the atom.
Analysing
7. Compare the properties of protons, neutrons and electrons.
8. Compare the models you illustrated in Questions 4 and 5.
Evaluating
9. Propose several reasons why models are useful in science. Explain the limitations of using models.
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WORKSHEET
Numbers of subatomic particles 1
Learning goals
At the end of this section, I will be able to:
1. Determine the number of protons and electrons in an element.
2. Calculate the mass of an atom from the number of protons and neutrons.
Figure 4.28 The periodic table gives you information about each element’s atoms. See Appendix for a larger version of the periodic table.
The number of subatomic particles in an atom depends on the type of element being considered. Look at the periodic table and you will notice that each element has a symbol, a name and two numbers. These numbers provide information about the number of protons, neutrons and electrons in each atom of that element.
The number at the top of the element symbol is called the atomic number. The atomic number is sometimes called the proton number because it tells you how many protons are in an atom of that element. For example, the atomic number of carbon is 6, because a carbon atom has six protons. atomic number the number of protons in an atom of an element
Atomic number
Figure 4.29 For the element carbon, the atomic number is 6. Therefore, you can conclude that it has six protons.
You will not find another element that contains six protons. This is because the atomic number defines the element. Any atom that contains six protons is carbon, no matter how many neutrons or electrons it contains. If another proton is added to carbon, then a different element with seven protons is formed – otherwise known as nitrogen. Carbon is a black solid and nitrogen is a colourless gas; one proton can make a big difference to an element’s physical properties! This is the same for any other element on the periodic table. Hydrogen has one proton, so any other substance with one proton will also be the element hydrogen.
4.32 For the element hydrogen, the atomic number is 1, so you can conclude that it has one proton.
1. Using an element of your choice as an example, explain what the atomic number tells you about the atom.
The atomic number also gives you information about the number of electrons in an atom of an element. Recall that protons have a positive charge and electrons have a negative charge. An atom is neutral, meaning that it has an overall charge of zero. For the overall charge to be zero (neutral), an atom must have the same number of positive protons and negative electrons. Carbon has an atomic number of 6, meaning it has six protons (six positively charged particles). Therefore, for the atom to have zero charge, it must also have six electrons (six negatively charged particles). So, the atomic number also tells you how many electrons an atom contains. If the number of electrons in an atom changes, the atom is now referred to as an ion and is said to be charged. This is denoted by a superscript plus (+) or minus (–) sign after the chemical symbol. A plus sign indicates that the atom has become more positive (lost negatively charged electrons), whereas a minus sign indicates that the atom has become more negative (gained negatively charged electrons).
For example, Mg2+ denotes a magnesium atom that has lost two electrons and now has an overall charge of 2+. It has 12 protons in the nucleus, but because it has lost two electrons it now only has 10 electrons. Atoms often become ions (by losing or gaining electrons) to obtain a stable filled outer shell (i.e. following the 2,8,8,2 rule).
Figure 4.33 When a magnesium atom loses two electrons, it becomes an ion with an overall charge of 2+ and a stable outer shell of 8 electrons.
Aim
To investigate the effect of different ions on water hardness.
Planning
1. Write a rationale about water hardness, what influences it and what problems hard water can cause.
2. Identify the independent and dependent variables for this experiment.
3. Identify as many controlled variables as possible and describe how you will manage them to prevent them affecting the measurements.
4. Develop a hypothesis to predict which ions will cause the hardest water.
5. Complete a risk assessment for this investigation, describing how any risks will be controlled.
Materials
• 8 test tubes
• 8 test-tube corks/bungs
• test-tube rack
• dropping pipettes
• 100 mL beaker
• marker pen
• 50 mL soap solution in industrially denatured alcohol. This can be made by dissolving soap flakes (or shavings from a bar of soap) in industrially denatured alcohol.
Method
• 10 mL distilled or deionised water
• 10 mL sodium chloride, 0.1 mol/L
• 10 mL calcium chloride, 0.1 mol/L
• 10 mL magnesium chloride, 0.1 mol/L
• 10 mL potassium nitrate, 0.1 mol/L
• 10 mL sodium sulfate, 0.1 mol/L
• 10 mL iron(II) sulfate, 0.1 mol/L
• 10 mL magnesium sulfate, 0.1 mol/L
1. Set up eight labelled test tubes in a test-tube rack. Place 1 cm depth of distilled water in one of the test tubes and place 1 cm of each of the seven ion solutions in the remaining test tubes.
2. Use a dropping pipette to transfer approximately 1 cm depth of soap solution to each test tube.
3. Seal the test tubes with a bung or cork and shake them well.
4. Record which test tubes contain a lather (mass of bubbles) at the end of the shaking. If a lather is present, record its depth.
Results
Draw a results table that will allow the collection of sufficient and relevant raw data.
Discussion
Identify the ion(s) that cause the most water hardness. Justify your answer with data.
1. Discuss the purpose of the test tube containing distilled water.
2. Identify any potential sources of error in this experiment.
3. Suggest any changes that could be made to the method to improve the quality of the data in future experiments. Justify your suggestions by explaining how each change would improve the data quality.
Conclusion
1. Draw a conclusion from this experiment about ions and water hardness. Justify your answer with data.
Charged
When the number of electrons in an atom changes, the properties of the element are affected. You are going to do some research into why this happens.
1. When fluorine atoms become negatively charged ions, they can combine with other elements, forming fluorides such as sodium fluoride (NaF). Conduct some research on the properties of fluorine and compare them with the properties of sodium fluoride.
2. The elements in the last group (column) of the periodic table are known as the noble gases. They all have a full outer shell of electrons and do not form ions readily. The elements in the second-last group of the periodic table (group 17) are known as the halogens, and they are all one electron short of a full outer shell. Conduct some research on what type of ions they form.
3. The elements in the first group of the periodic table are known as the alkali metals. They all have one electron in their outer shell. Consider whether it would be easier to donate one electron to have a full outer shell, or to try to gain seven electrons. Conduct some research on what type of ions they form.
4. The elements in the second group of the periodic table are known as the alkaline earth metals. They all have two electrons in their outer shell. Conduct some research on what type of ions they form.
5. Predict the charge of the ion formed from:
a) sulfur
b) barium c) iodine.
1. Explain how an atom becomes positively or negatively charged.
2. An atom of oxygen gains two electrons and becomes an ion. State the ion formed, using the atomic symbol for oxygen and its charge.
mass number
the sum of the protons and neutrons in the nucleus of an atom
relative atomic mass
the average mass of an atom when considering all natural isotope masses and their abundances
isotopes
atoms of the same element with the same number of protons but a different number of neutrons
The mass number of an atom is the sum of the protons and neutrons in the nucleus. The mass number is a whole number and is not found in the periodic table for any elements. Do not confuse it with the second number that is listed for every element in the periodic table, the relative atomic mass. Electrons are not considered when calculating the mass number because their mass is so small that it is considered negligible.
The second number listed for each element in the periodic table is called the relative atomic mass and it is seldom a whole number (see Figure 4.34). This is because every element consists of a mixture of atoms that have the same number of protons but different numbers of neutrons. Such atoms are called isotopes and will be discussed later in the chapter. The relative atomic mass shows the average mass of an element’s atoms when considering all natural isotope masses and their abundances.
Relative atomic mass
Figure 4.34 The atomic symbols for carbon showing the atomic number of 6 and relative atomic mass of 12.01. These numbers can be used to estimate the number of neutrons in a carbon atom.
Thus, for a single atom, the mass number can be calculated by the following equation:
Unlike for protons, changing the number of neutrons in an atom of an element will not change the type of element, but it will change its physical properties, such as density.
Worked example 4.1
An oxygen atom has an atomic number of 8 (8 protons) and a mass number of 16. Calculate the number of neutrons.
Mass number = number of protons + number of neutrons 16 = 8 + number of neutrons
Number of neutrons = mass number –number of protons
Number of neutrons = 16 – 8 = 8
Substitute the known numbers (mass number and number of protons) into the equation.
Rearrange the equation to solve for the number of neutrons.
1. Locate the following elements on the periodic table. Using their atomic numbers and relative atomic masses (rounded to the nearest whole number), state the number of protons, neutrons and electrons in each atom.
Section 4.3 review
Online quiz
Section 4.3 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. State the names of the two numbers that accompany each element on the periodic table.
2. Identify which of the numbers you named in Question 1 is always the largest.
3. State the name of the element that has an atomic number of 20.
Understanding
4. An atom has a mass number of 45 and an atomic number of 16. Calculate how many neutrons it has. Show your working.
5. Identify the subatomic particles that have nearly the same mass.
Applying
6. Explain why the mass of the electron is not considered in the mass number.
7. Copy and complete the table using the information in the periodic table to summarise the structure of the three elements listed.
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Analysing
8. Compare the mass number and the atomic number of an element.
9. Write the electron configuration of a chloride (Cℓ–) ion if a chlorine atom has 17 electrons.
Evaluating
10. ‘The mass number determines the identity of the element.’ Propose whether this statement is true or false. Justify your answer.
11. Justify why no two elements on the periodic table have the same atomic number.
12. Evaluate the statement: ‘Atoms are always neutral.’
WORKSHEET Isotopes
At the end of this section, I will be able to:
1. Define ‘isotope’ and ‘radioactive half-life’.
2. Describe three types of nuclear radiation.
3. Compare the ionising and penetrating power of alpha, beta and gamma radiation.
Earlier in this chapter, you learned how changing the number of protons in an atom results in a different element. You also saw how changing the number of electrons results in a charged atom called an ion. Now you will learn what happens when the number of neutrons in an atom is altered.
Two atoms that have the same atomic number but different mass numbers are called isotopes. Isotopes have the same number of protons as each other (same atomic number; therefore, the same element), so their different mass numbers must be explained by having a different number of neutrons, because the mass of electrons is considered negligible.
The existence of isotopes was first proposed by Frederick Soddy in 1913. He noticed that atoms of the same element could have different atomic masses but behave in the same way. He named these elements isotopes, which means ‘same place’, because they were in the same place on the periodic table. Scientists could not explain why this occurred until James Chadwick discovered the neutron.
Figure 4.35 In 1913, Frederick Soddy discovered isotopes in his work on uranium, which earned him the Nobel Prize in Chemistry in 1921.
Let’s look at an example. Carbon exists naturally in three forms (see Figure 4.36). All three of these forms are the element carbon because they all have an atomic number of 6 (6 protons).
Figure 4.36 The three naturally occurring isotopes of carbon
Notice that the three forms of carbon have different mass numbers (12, 13 and 14). This difference in mass number is because they have different numbers of neutrons. Remember that the number of neutrons in an atom is calculated by subtracting the atomic number from the mass number.
Therefore, the first form of carbon has six neutrons, the second has seven and the third has eight. Because they have different numbers of neutrons but the same atomic number, they are called isotopes of carbon.
Note that the relative atomic mass of an element shown on the periodic table is the average mass of all naturally occurring isotopes of that element. For example, the relative atomic mass of carbon is 12.01 because most carbon atoms have a mass of 12, but a small number of atoms naturally occur with a mass of 13 or 14.
Isotopes are named by writing the element name first and then the mass number. For example, the three isotopes of hydrogen are hydrogen 1 (H 1), also known as protium, hydrogen 2 (H 2), known as deuterium, and hydrogen 3 (H 3), known as tritium.
Another way of showing isotopes is to use a symbol notation. Notice that on the periodic table the atomic number is written at the top; this is because the atomic number is used to define the element.
When you write the symbols for isotopes, often a nuclide notation is used, whereby the mass number is written on the top left hand side of the element symbol and the atomic number is written on the bottom left hand side of the element symbol (see Figure 4.37).
Figure 4.37 The three naturally occurring isotopes of hydrogen in nuclide notation
The stability of an isotope is based on whether it is likely to break down or decay into other elements. Often, heavy isotopes (that is, those that have many more neutrons than protons) are unstable compared to lighter isotopes (those that have similar numbers of neutrons and protons), which are stable. Unstable isotopes, such as the isotopes of the elements uranium and plutonium, are often called radioisotopes. In these types of isotopes, radioactive decay occurs to achieve a stable nucleus (as discussed later in this section). Stable isotopes are not radioactive, or are radioactive to a much lesser extent, because their nucleus is stable and therefore not prone to radioactive decay. Elements can have more than one stable isotope, such as carbon 12 and carbon 13. Table 4.3 summarises the differences between stable and unstable isotopes.
nuclide notation a symbol notation in which the mass number is shown at the top left of an element symbol and the atomic number at the bottom left radioactive decay when an unstable nucleus emits radiation (alpha and beta particles or gamma waves) as it breaks down to form another element
Table 4.3 A comparison between stable and unstable isotopes
The mass number of chlorine on the periodic table is 35.45. If you were to use this number to work out the number of neutrons, then it would have 18.45 neutrons. This is incorrect because 0.45 of a neutron cannot exist. Conduct some research into why this is the case.
1. Why is the mass number of chlorine recorded as 35.45 on the periodic table?
2. Chlorine has two naturally occurring stable isotopes, Cℓ-35 and Cℓ-37. What is the difference between Cℓ-35 and Cℓ-37?
3. Given the mass number of chlorine, which isotope of chlorine do you think is more abundant in nature?
WIDGET Nuclear equations
WORKSHEET
Radioactive decay
Quick check 4.9
1. Define ‘isotope’.
2. Explain how you would name an isotope of magnesium that has a mass number of 25.
Did you know? 4.4
missing mass numbers
Look at francium (Fr) on the bottom left of the periodic table. It doesn't have a mass shown. Elements written like this are radioactive, so they are very unstable, and so a stable relative atomic mass is not shown. Can you find other radioactive elements on the periodic table?
Figure 4.38 Marguerite Perey was a French physicist who discovered the element francium, which is one of the rarest and most unstable elements on the periodic table. She was the first woman to be elected to the prestigious French Academy of Sciences.
Quick check 4.10
1. Recall the characteristics of unstable isotopes.
When a radioactive nucleus decays, some of the energy stored in the nucleus (nuclear energy) is transformed into different types of energy. Energy is always conserved, so the decay of the nucleus converts nuclear energy into other forms of energy, such as heat and light. Kinetic energy in the form of moving particles might also be emitted. Emission from radioactive decay is commonly in the form of alpha (α) and beta (β) particle decay or emission of high energy light waves in the form of gamma (γ) radiation.
An alpha particle consists of two protons and two neutrons, which is the same as the nucleus of a helium atom (without electrons). Therefore, when an atom undergoes alpha decay, the atomic number decreases by 2 and the mass number decreases by 4. When the atomic number changes, a new element is formed. In this case, the element has two fewer protons. The equation in Figure 4.39 shows what happens when an atom of radon 222 undergoes alpha decay. Note: An alpha particle can be shown as either 2 4 He or 2 4 α and has a charge of 2+.
Figure 4.39 When a radon-222 atom undergoes alpha decay, it becomes a polonium-218 atom. The atom of radon has changed into an atom of polonium.
As a helium nucleus is emitted, the radon 222 atom loses two protons and therefore becomes a polonium atom. The mass number also decreases by 4 from 222 to 218. The emitted He 4 is often described as an alpha particle.
Beta particles are simply fast moving electrons emitted from the nucleus. During beta decay, a neutron is transmuted (changed) into a proton and an electron. The atomic number therefore increases by one, which changes the identity of the element. The mass number of the remaining atom is not affected, because it has lost a neutron but gained a proton. The equation in Figure 4.40 shows what happens during beta decay. The iodine 131 atom gains a proton and loses a neutron to become a xenon atom, and a high energy beta particle (electron) is emitted. Note: A beta particle can be shown as either 1 0 e or 1 0 β.
Figure 4.40 When an iodine-131 nucleus undergoes beta decay, it becomes a xenon-131 atom and emits a beta particle.
Gamma decay is different from alpha and beta decay in that the atom undergoing gamma decay is not changed; that is, the mass and atomic numbers are not altered. This is because gamma decay involves the emission of a high energy wave (gamma ray) rather than a particle. The equation in Figure 4.41 shows the gamma decay of radioactive cobalt 60. Because the cobalt 60 nucleus is unstable, it is said to contain more nuclear energy than required for stability and an asterisk (*) is included next to the mass number in the nuclide notation. The * indicates that the nucleus is excited or has more energy. A gamma ray is a wave of energy with no mass or charge, so the cobalt 60 atom is unchanged. However, the * is removed to denote that the nucleus is no longer excited.
Figure 4.41 When an excited cobalt-60 nucleus decays, a gamma ray is emitted.
beta particle a negatively charged particle (electron) that is emitted from the nucleus of some radioactive elements during radioactive decay (disintegration) of an unstable atom gamma ray a type of electromagnetic radiation that has high energy and a very short wavelength; produced when certain radioactive atoms decay
As previously discussed, a gamma ray is a high energy wave and unlike the emissions from alpha and beta decay. You might be surprised to learn that this emission is a form of electromagnetic radiation with properties similar to visible light!
marie Curie
Marie Curie was the first woman to be awarded a Nobel Prize and is the only person to have been awarded two Nobel Prizes in different scientific fields: Physics in 1903 (with her husband, Pierre Curie, and Henri Becquerel) and Chemistry in 1911.
Conduct some research on the work of Marie and Pierre Curie that led to their scientific discoveries in radiation as well as the experiments that validated their discoveries.
Irène Joliot-Curie was a French physicist and chemist and the daughter of Marie Curie. She, along with her husband Frédéric Joliot-Curie, discovered artificial radioactivity in 1934. This discovery allowed scientists to produce new isotopes of elements that did not exist in nature.
Joliot-Curie’s work on isotopes helped to advance our understanding of nuclear physics and chemistry, and she became the second woman to win a Nobel Prize after her mother.
Ionising and penetrating powers
How dangerous a type of radiation is depends on its ability to penetrate materials and how much damage it can do (how ionising it is). Figure 4.44 and Table 4.4 summarise the properties of the three types of radiation.
4.44 The penetrating powers of alpha, beta and gamma radiation
Type of radiationPenetrating power
Alpha Least penetrating. Can be stopped by a sheet of paper
Beta Can penetrate paper but is stopped by a thin aluminium sheet
Gamma The most penetrating. Can only be stopped by thick pieces of lead or concrete
Table 4.4 Properties of the three different types of radiation
Ionisation power
Very strongly ionising because it is a 2 42 He + ion; can cause the most damage, especially if inside the body
Not as ionising as alpha particles but more ionising than gamma rays
Not very ionising so causes the least damage; can penetrate the body, and high-energy gamma rays are used to kill cancer cells
1. If an atom emits alpha radiation, identify the particle it gives off and how the atom is changed as a result.
2. If an atom emits beta radiation, identify the particle it gives off and how the atom is changed as a result.
3. Describe how gamma radiation differs from alpha and beta radiation.
Some radioactive elements decay extremely quickly – over seconds, minutes or hours – while others decay steadily over thousands or millions of years. The time taken for half of the atoms in a sample of radioactive material to decay is known as the half-life. This is a useful value for comparing radioactive elements as well as estimating the age of radioactive materials.
Carbon 14 is a radioactive isotope of carbon with a half life of approximately 5730 years. This means that a pure sample of carbon 14 takes about 5730 years for half of its atoms to decay, in this case usually by beta decay to nitrogen 14. The abundance of carbon 14 and nitrogen 14 in a fossil can be analysed over time to identify the possible age of the fossil.
Uranium 238 is a naturally occurring isotope with a very long half life of about 4.5 billion years, undergoing primarily alpha decay to form thorium 234. In contrast, an isotope of fluorine 18, used in medical imaging, has a half life of about 109 minutes. That means fluorine 18 must be prepared at the medical facility and used very quickly because it will all decay in a few hours!
1. Define radioactive ‘half-life’.
2. Write a nuclear equation for:
a) beta decay of C-14 b) alpha decay of U-238.
There are about 90 naturally occurring elements, with about 250 stable isotopes and about 3200 unstable radioisotopes. Stable isotopes and radioisotopes both have important uses.
Perhaps the most well known use for isotopes is in medicine to diagnose and treat illnesses: cobalt 60 (Co 60) is used in radiotherapy to treat cancer cells; strontium 90 (Sr 90) is used in the treatment of skin cancer; and gamma rays are produced when radioisotope decay is used to kill bacteria that may be on medical equipment.
Iridium 192 is a useful radioisotope with a half life of about 74 days, which also gives it some longevity for application. It can be used as a diagnostic tool for finding faults in materials such as pipelines and materials used in aircraft and spacecraft. Iridium 192 primarily decays by beta decay and gamma decay. These emissions penetrate materials to a different extent and thus the emissions can be used to image the inside of materials by detecting radioactive emissions that can pass through different materials.
Figure 4.45 A patient undergoing radiotherapy for cancer
Science inquiry 4.2
Carbon-14 is an isotope of carbon that primarily decays by beta radiation to nitrogen-14 at a consistent rate. Scientists can predict the age of a fossil by examining the relative amounts of carbon-14 and nitrogen-14 in an organic fossil, in a technique known as radiocarbon dating. Carbon dating techniques are continuously improving, allowing more accurate dating.
In early 2020, a team of researchers from around Australia collaborated on dating Aboriginal Peoples’ rock art in the Kimberley region of Western Australia. Dating rock art can be challenging because much of the carbon in the organic ochre has degraded. Instead, the team of researchers radiocarbon dated overlying and underlying mud-wasp nest fossils to provide an age range for the paintings. A lot of the rock art in the area ranged from 10 000 to 12 000 years old, with some over 20 000 years old!
Practical 4.3: Self-design and teacher demonstration
Investigating the penetration of alpha, beta and gamma radiation
You have been provided with the materials listed below. Suggest an experiment that could be done using this equipment to show the penetrating properties of alpha, beta and gamma radiation. You may wish to draw a diagram or write a method to demonstrate that you have done this task.
Aim
To investigate the penetrative strengths of ionising radiation.
Materials
• alpha radiation source
• beta radiation source
• gamma radiation source
• Geiger–Müller tube (detects radiation)
• absorbing materials: sheet of paper, aluminium sheet, lead sheet
Method
Your teacher will demonstrate the experiment. This experiment emits dangerous radiation, so it can only be performed by a teacher and under strictly controlled conditions.
Results
Copy and complete the following table.
Table showing penetrating power of different types of radiation
Radiation Material that stops most of the radiation from passing through
Alpha
Beta
Gamma
Discussion
1. Identify the most penetrating radiation and justify your choice.
Penetrating power
2. Propose which type of radiation you think could cause the most damage if it gets into our bodies.
3. Conduct some research on the effects that radiation can have on the body to explain why it is so damaging.
4. Discuss how the experiment could be modified to show the effectiveness of the radiation over different ranges and thickness of absorbing materials.
Radioactivity is used in novel technologies, even in your own home! Ionisation chamber smoke detectors can detect very small amounts of smoke in a domestic household, even before the occupants can smell smoke in the air.
An ionisation chamber in the smoke detector contains a very small amount of americium-241 (Am-241) foil. This radioactive element decays, emitting alpha and gamma radiation as shown in the following equations:
The alpha particles emitted are very strongly ionising and ionise the air in the chamber. This means the air in the chamber conducts electricity. If smoke particles enter the chamber, the electrical current is disrupted and the smoke detector sounds an alarm.
While this nuclear reaction might be happening in your own home, there is no need to worry. The radiation emitted by domestic smoke detectors is less than 40 kilobecquerels (kBq), which is considered safe under Western Australian state regulation.
Go online to access the interactive section review and more!
Section 4.4 review
Online quiz
Section 4.4 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Determine the name of an isotope of barium with a mass number of 130.
2. Determine the name of an isotope of potassium with 22 neutrons.
3. Name three important uses of radioisotopes.
Understanding
4. Describe the relationship between the mass of an isotope and its stability.
Applying
5. Summarise what happens to the nucleus of an element during alpha decay.
Analysing
6. Contrast stable isotopes and radioisotopes.
7. Compare these isotopes of sodium: Na-23 and Na-24.
Evaluating
8. Construct an equation to show the alpha decay of uranium-235 to thorium-231.
9. An element undergoes radioactive decay, but its atomic number and mass number are not affected. Deduce the type of decay.
10. During the radioactive decay of an isotope, a high-energy electron is released. Deduce the type of decay.
Chapter checklist
Success criteria
Linked questions
4.1I can discuss how the model of the atomic structure was developed.7, 10, 19, 21, 22
4.2I can distinguish between protons, neutrons and electrons. 2, 4, 15
4.3I can determine the subatomic particles in an atom, using information from the periodic table. 11, 20
4.4I can describe how isotopes of an element differ from each other.14
4.4I can discuss the different forms of radioactive decay. 6, 14, 17
4.4I can define ‘radioactive half-life’. 3
Scorcher competition Review questions Data questions
Reviewquestions
Remembering
1. State the names of the three subatomic particles within the atom.
2. Recall the relative charge of each subatomic particle:
a) proton b) neutron c) electron.
3. Define ‘radioactive half-life’.
4. State where protons and neutrons are located within an atom.
5. If a neutral atom has 18 protons, state how many electrons it has.
6. Recall the type of particle that is released during beta decay.
Understanding
7. Describe the planetary model of the atom.
8. Explain why atoms of elements have a neutral overall charge.
9. Write the electron configuration for a Ca atom with 20 electrons.
10. Explain how Rutherford’s gold foil experiment led to the discovery of the nucleus.
Go online to access the interactive chapter review
Applying
11. Summarise the three main isotopes of neon. You may do so in a table like the one shown here.
IsotopeMass
12. Apply your knowledge of the overall charge of an atom to explain what would happen to an oxygen atom if it had an extra electron (nine electrons).
13. Explain why neutrons were difficult to discover.
14. Describe the differences between isotopes of the same element.
Analysing
15. Compare the properties of the subatomic particles in terms of their mass and charge.
Evaluating
16. Deduce the relationship between the mass of an element and how stable it is.
17. Ionising radiation is used in smoke detectors. Decide which type of radiation you would choose for this use and why.
18. Propose why radioactive sources in schools must be stored in lead-lined boxes.
19. Democritus and Aristotle were philosophers, not modern scientists. In what ways were their thoughts ‘scientific’ and in what ways were they ‘not scientific’? Discuss how significant their contributions were to atomic theory.
20. Write a nuclear equation for the beta decay of iridium-192.
21. ‘The current atomic model is perfect and accurate.’ Evaluate the accuracy of this statement.
22. Discuss whether you expect the atomic model to change significantly in the future. Justify your answer.
23. Deduce why there is usually such a long period between a scientist proposing a theory and the theory being supported or refuted by valid scientific evidence.
The isotope carbon-14 decays by beta radiation to form nitrogen-14 atoms, following the decay curve in Figure 4.48. Scientists can predict the age of a fossil by using analytical techniques that measure the relative abundance decay curves of carbon-14 and nitrogen-14 in the fossil.
0 5
02865573085951146014325171902005522920257852865031 515
Figure 4.48 The relative abundance of carbon-14 (blue line) and nitrogen-14 (orange line) in an initial sample of carbon-14 over 31 515 years
1. A scientist has measured the relative abundance of carbon-14 in a sample of First Nations Australian rock art at 25% compared to nitrogen-14. Determine the age of the rock art.
2. The relative abundance of nitrogen-14 in a kangaroo fossil sample is 40%. Calculate the relative abundance of carbon-14.
3. Identify the relative abundance of nitrogen-14 in a fossil dated at 8595 years old.
4. Contrast the two curves and comment on the relative rate of decay of carbon-14 and the growth of nitrogen-14.
5. Deduce the half-life (time taken for half the carbon-14 to decay to nitrogen-14) of carbon-14.
6. After 28 650 years, the relative abundance of carbon-14 is 3.125%. Predict the relative abundance of nitrogen-14 after another 5730 years (34 380 years total).
7. Predict and explain whether it would be possible to find a fossil with a relative abundance of carbon-14 of 0%.
8. The use of radiocarbon dating is most efficient with fossils less than 20 000 years old. Compare the carbon-14 decay curve before and after 20 000 years and elaborate on this comment.
Plastic is one of the most commonly used substances today. It is used for everything from food packaging to toys, from building materials to clothing, and even medical implants. Plastic was invented in 1907 and has revolutionised the manufacturing of a multitude of products because of its versatility. Plastic can be hard, soft, stretchy, bendable, strong or durable.
Molecules are atoms that are chemically bonded together. Chemically, plastic consists of long chains of molecules called polymers. This is why the names of many plastics start with ‘poly’.
The polymers are made up of carbon and hydrogen, and sometimes oxygen, nitrogen, sulfur, phosphorus, fluorine or silicon.
Design and create a product using bioplastics.
There are two main problems with the amount of plastic that is used. First, most plastic is made from crude oil, a limited resource that is harmful to the environment to extract. Second, because of its molecular structure, plastic is very difficult to biodegrade (break down).
Plastic litter builds up in waterways and kills wildlife, as well as leaching harmful toxins into the environment.
bioplastics are a type of plastic made from renewable resources such as plants. They can easily be made at home with readily available ingredients. Although they cannot solve the plastic problem alone, they can reduce carbon dioxide emissions, and some have the potential to biodegrade more easily than traditional plastics.
In groups of two or three, your task is to think of a product that is made of plastic and find a way of making it out of bioplastic.
• corn starch
• vinegar
• glycerine
• water
• food dye (optional)
• saucepan
• wooden spoon
• hotplate
• non-stick/baking paper/aluminium foil and tray
• cookie cutters or moulds to shape the plastic
• safety glasses
Wear safety glasses. Be very careful when working around the hotplate and handling the hot mixture. Ensure the hotplate is cool before moving it.
1. In your group, discuss different plastic products you use in your everyday life, and list all the benefits of manufacturing these products as a bioplastic.
2. List all the restrictions you must consider in your design, based on the materials and space you have available.
3. Conduct some research into how you would use the suggested materials, or other materials that are safe for use in a school science laboratory, to manufacture the bioplastic.
4. Decide on a plastic product that you could make using a bioplastic. Justify your choice as a group by considering your constraints.
5. Design the method for manufacturing the bioplastic.
6. Design the mould you will use for making your product.
7. Create the mould you will use for your bioplastic product.
8. Follow your design method and construct your bioplastic product solution. Remember, it may take a week for your bioplastic to set.
9. Describe any difficulties you encountered when creating your product out of the bioplastic.
10. Suggest ways to improve the design of your product.
11. List the physical properties of your bioplastic and comment on how appropriate these properties are for your product.
12. Test your product by using it for its intended purpose under different conditions.
13. Evaluate the effectiveness of your product.
Introduction
The modern-day periodic table organises all 118 elements based on properties such as chemical reactivity, but the periodic table has not always had the structure it has today. In this chapter, you will explore the scientists whose work debated and changed the organisation of the elements over time, and identify the helpful trends observed in the periodic table today. The electron shell structure will be examined, as well as how the number of valence electrons in an atom affects the chemical reactivity of elements to create chemical compounds.
Groups (vertical columns)
Periods (horizontal rows)
divided into
The periodic table is the result of many years of scientific research and progress.
Section 5.1
Section 5.2
Section 5.3
Special groups of elements:
• metals, non-metals, metalloids
• transition metals
• lanthanoids and actinoids
• group 1 – alkali metals
• group 2 – alkaline earth metals
• group 17 – halogens
• group 18 – noble gases
Valence electrons affect element properties.
Ionic compounds Covalent compounds
Chemical sciences
The structure and properties of atoms relate to the organisation of the elements in the periodic table; elements in the same group on the periodic table have similar properties
• exploring the periodic table to examine the similarities and differences between and within groups of elements, such as alkali metals, alkaline earth metals, transition metals, metalloids, non-metals, halogens and noble gases
• exploring the reactivity of metals with water through experimentation and relating reactivity to their position on the periodic table
• modelling the atomic structure of elements, including electron configuration 5.2
• modelling the structure of atoms from the same and different groups on the periodic table to determine structural similarities and differences
Compounds are formed when atoms lose, gain or share electrons; non-metal elements combine to form covalent substances; positively charged ions and negatively charged ions combine to form ionic compounds; compounds can be represented using chemical formulae and models
• recalling the chemical formulae for common covalent substances, such as water, carbon dioxide, oxygen gas and hydrochloric acid
• producing, collecting and testing covalent gases experimentally, such as oxygen, carbon dioxide and hydrogen
• using a table of common ions to write chemical formulae to represent ionic compounds, such as sodium chloride, magnesium chloride and iron oxide 5.3
• exploring the conductivity of salt solutions experimentally STEM activity
© School Curriculum and Standards Authority
Glossary terms
Learning goals
At the end of this section, I will be able to:
1. Recall the scientists in the timeline of the periodic table.
2. Describe the structure and property trends in Mendeleev’s periodic table.
How to best organise the known elements has been a topic of scientific debate since the late 1700s. In this section, we will follow the work of six scientists who influenced the shape and structure of the periodic table.
1808
1817
Antoine Lavoisier
• Lavoisier discovered and named the elements oxygen and hydrogen.
• In 1789, there were thought to be 33 elements (including light). Lavoisier sorted these elements into gases, metals, non-metals and earths, constructing the first list of the known elements.
• His table of elements quickly became outdated as new elements were discovered.
John Dalton
• Dalton was a chemist, physicist and meteorologist. He developed early atomic theory and published a table of relative atomic masses.
• Dalton allocated symbols to the 36 known elements. These were later replaced by the notation devised by Jöns Jacob Berzelius, which is still used today.
Figure 5.1 Dalton’s element symbols
Johann Wolfgang Döbereiner
• Döbereiner noticed that known elements could be arranged into groups of three by their similarities in appearance and reactions. He called these groups triads (for example, lithium, sodium, potassium). He found that, when the elements in a triad were placed in order of their atomic mass, the middle element had a mass that was the average of the other two.
• Döbereiner’s work encouraged others to look for patterns in chemical properties and atomic weights.
Figure 5.2 Two Döbereiner triads
1862
1864
1869
Alexandre-Émile Béguyer de Chancourtois
• de Chancourtois arranged the known elements by their increasing atomic mass.
• The atomic mass of oxygen was set at 16 and used as a standard for all the other elements. He wrapped his list around a cylinder, which allowed sets of similar elements to line up. Because tellurium was situated in the middle of the cylinder, he named his system the telluric screw.
• The first geometric representation of periodic law was created, meaning that de Chancourtois’s system showed repetition in the properties of elements at certain, regular intervals.
John Newlands
• Newlands listed the known elements in order of their atomic masses, in horizontal rows, seven elements long.
• He stated that the eighth element would have similar properties to the first element in the series. This was known at the time as the law of octaves.
• His work was the first time anyone had used the sequence of atomic masses to organise the elements.
5.4 Newland’s law of octaves. Every eighth element in the row has similar properties. Track the lines and investigate what is similar about each element.
Dmitri Mendeleev
• By 1869, 56 elements were known and a new element was being discovered approximately every year.
• Mendeleev organised the elements into a table according to their properties and in order of their atomic mass.
• Mendeleev left space in his table for elements he thought would later be discovered.
5.5 Mendeleev’s early attempt at arranging the known elements into a table
1. Determine the atomic mass of element Y using Döbereiner’s method if X, Y and Z form a triad.
2. Describe how Mendeleev’s attempt was similar and different to those made by other scientists.
Mendeleev’s approach differed from other scientists in that he left space for elements that had not yet been discovered; he knew that new elements were being discovered regularly in the 1800s. Figure 5.5 shows that he drew lines to denote a missing piece in his arrangement.
Mendeleev left calculated spaces in his periodic table where he thought the elements would have similar properties to those above and below. For example, he predicted an element between silicon (Si) and tin (Sn), shown in Figure 5.6.
He named this element eka-silicon and made the predictions shown in Table 5.1 based on the known properties of the elements above and below it in the periodic table. He was close! In 1886, the element germanium (Ge) was discovered with the properties described in Table 5.2. The discovery of germanium occurred within Mendeleev’s lifetime and confirmed his arrangement.
Table 5.1 Mendeleev’s predictions for the chemical properties of eka-silicon
5.6 Mendeleev predicted that there would be an element between silicon and tin.
Table 5.2 The chemical properties of germanium
While Mendeleev’s work had a great influence on the work of all chemists attempting to organise the elements in the periodic table, it did not earn him a Nobel Prize. However, in 1955, scientist Albert Ghiorso and colleagues discovered element 101 and named it Mendelevium (Md) after the ‘father of the periodic table’.
The periodic table organises the known elements based on various properties, but has it reached its final form? Consider the following exercise.
1. Review: how did the periodic table get to be the way it is now?
2. Predict: how else might it change in the future?
3. Imagine and create: future changes might come with challenges. How could you turn these challenges into opportunities for the scientific community?
Aim
To investigate the relationship between the position of an element in the periodic table and its density.
Useful formulas
Density (g/cm3) = mass (g) volume (cm3)
Percentage difference = (actual value predicted value) actual value × 100
Materials
• sample elements (carbon rod, silicon, tin)
• 50 mL measuring cylinder
• graph paper
• balance
• ruler
• weigh boats (small containers to hold sample elements)
Method
Part 1: Prepare the results table
1. Copy the results table into your science journal.
2. In your results table, for each element used in this experiment state its position on the periodic table.
3. Identify the dependent variable in your table. (HINT: Which property are you investigating?)
Table showing properties of carbon, silicon and tin
Element
Part 2: Measure the mass of each sample element
1. Place a weigh boat onto the balance and zero the balance by pressing ‘tare’.
2. Place the first sample element on the empty weigh boat and record the mass in your table.
3. Remove the sample element.
4. Repeat steps 1–3 with the other sample elements.
Part 3: Measure the volume of each sample element
1. Half fill a 50 mL measuring cylinder with water and record the initial volume in cubic centimetres (1 mL = 1 cm3).
2. Gently place the first sample element into the measuring cylinder and record the new volume in the table.
3. Remove the sample element by tipping the water out of the measuring cylinder.
4. Repeat steps 1–3 with the other sample elements.
Results
Calculate and graph the densities
1. Calculate the volume of each sample element in cubic centimetres and record it in the results table.
2. Calculate the density of each sample element using the given formula and record it in the results table.
3. Draw a scatterplot to analyse the relationship between the period numbers and densities of different elements.
4. Add a line of best fit to the graph, if possible. Note the type of line that fits best to reflect the relationship between the two variables.
5. Describe the trend or pattern you observed when the line of best fit was applied to the graph. What type of relationship is indicated?
6. Use your graph to predict the densities of germanium (row 4) and lead (row 6). Record the predictions in your science journal.
Discussion
1. Compare the actual density of each element (obtained from secondary data sources; the ‘properties’ tab at ptable.com is a good resource to use) with its calculated density.
2. Compare the actual densities of carbon, silicon and tin to the densities calculated mathematically by calculating the percentage difference using the given formula.
3. Was the calculated density data reliable enough to base predictions on? Justify your response with data.
4. Research online to find the actual densities of germanium and lead (the ‘properties’ tab at ptable.com is a good resource to use). Record the actual density of each in your science journal.
5. Compare the actual densities of germanium and lead to the densities predicted mathematically by calculating the percentage difference using the given formula.
6. Can reliable conclusions and predictions be drawn from the results? Justify your response with data.
7. Can you identify possible limitations of this method? Justify your answer using data if possible.
8. Suggest any changes that could be made to the method to improve the quality of the data in future experiments. Justify your suggestions by explaining how each change will improve the data quality.
The modern periodic table is a list of all the known elements in order of their atomic number. The atomic number of an element is the number of protons it has. This makes hydrogen (H) the first element in the periodic table because it has one proton and therefore an atomic number of 1. Oganesson (Og), a synthetic element discovered by Russian scientists in 2002 and officially named in 2016, is currently the last element. It has an atomic number of 118, which means it has 118 protons. Oganesson is nicely placed in the last place of the noble metals in group 18, but that does not mean the periodic table is now finished! Elements with atomic numbers greater than 118 are possible, and scientists are working to discover these new elements. Where might they go on the modern periodic table?
You may have noticed that many elements have symbols that don’t match their English names. Some of them have interesting stories!
Research the source of the symbol for the following elements:
• Sodium (Na)
• Gold (Au)
• Iron (Fe)
• Silver (Ag).
• Lead (Pb)
The periodic table is arranged into vertical columns called groups. There are 18 groups in total.
Elements in the same group generally have similar chemical properties; for example, they react with the same chemicals in similar ways. This lets us predict the chemical properties of elements by looking at others in the same group. For example, sodium, an element in group 1, reacts violently when placed in water. Therefore, we can expect that potassium, also in group 1, will react in a similar way.
Quick check 5.2
1. Decide whether the following statements are true or false.
a) Groups are the vertical columns in the periodic table.
b) Oxygen (O) is in group 5.
c) Because strontium (Sr) is in the same group as silicon (Si), it will have similar properties.
2. Barium (Ba) in group 2 reacts with oxygen (O) to form barium oxide, a metal oxide with the formula BaO. Potassium (K) in group 1 reacts with oxygen (O) to form potassium oxide with the formula K2O. An unknown element was reacted with oxygen. The product was a metal oxide with the formula XO (X being the unknown element). Explain which group you would place the unknown element into.
group a vertical column in the periodic table
Figure 5.10 The group 1 metals all have similar properties and therefore behave in similar ways.
period a horizontal row in the periodic table electron the smallest subatomic particle in an atom; electrons are arranged around the nucleus in shells
In the periodic table, groups are the vertical columns and periods are the horizontal rows. There are seven periods in total.
It is often easy to skip over hydrogen (H) and helium (He), but these two elements make up the first period of the periodic table. As you move across a period, the atomic number increases (that is, the number of protons increases), as does the number of electrons, which fills the electron shells in the order 2,8,8,2 as you learned in the previous chapter.
Figure 5.11 Periods are the horizontal rows in the periodic table.
This arrangement into groups and periods means that each element has a specific position on the periodic table. For example, carbon (C) is placed in group 14, period 2, and helium (He) is in group 18, period 1. You might wonder why helium is not placed next to hydrogen, in group 2. Helium has a full outer shell of electrons and behaves like all the other group 18 ‘noble gases’, being very unreactive. You will learn more about this in the next section. Quick check 5.3
1. Decide whether the following statements are true or false.
a) Periods are the horizontal rows in the periodic table.
b) Lithium is in period 1.
2. State the position (group and period) of the following elements in the periodic table.
a) copper (Cu)
b) calcium (Ca)
c) neon (Ne)
d) aluminium (Aℓ)
Remembering
1. Recall the names of three scientists who attempted to organise elements.
2. Recall who created the first version of the modern periodic table.
3. Recall the method that most scientists used to arrange chemical elements.
4. State the modern-day arrangement of elements for which Döbereiner’s triads were the forerunner.
5. Using Döbereiner’s law of triads, calculate the mass of element B.
Understanding
6. Explain why de Chancourtois’s arrangement was superior to Döbereiner’s.
7. Summarise how Mendeleev made his predictions about the properties of elements that had yet to be discovered.
Applying
8. Compare Newlands’ and Mendeleev’s arrangements.
9. Critique de Chancourtois’s arrangement of the elements.
Analysing
10. Propose the reasons why Mendeleev’s periodic table was accepted.
11. Discuss the reasons why multiple ways of arranging the chemical elements were proposed throughout history.
Evaluating
12. Determine the properties of the middle element in the tables below. a)
b)
c)
13.Determine why the modern periodic table has remained relatively unchanged since it was reordered by atomic number instead of atomic mass.
Go
Learning goals
At the end of this section, I will be able to:
1. Identify elements as metals, non metals or metalloids.
2. Recall the physical properties and chemical reactivity trends in group 1 and 2 metals.
3. Recall the physical properties and chemical reactivity trends in group 17 and 18 non-metals.
Generally, the periodic table groups elements based on similar chemical properties, such as reactivity. This is more true in some groups of the periodic table than others. Groups 1, 2, 17 and 18 are examples of groups that have consistent chemical properties down the group in the periodic table. Elements in a group tend to have the same number of valence electrons, which is the number of electrons in the outer electron shell and is the primary factor that influences chemical reactivity. Atoms that have a full outer shell of electrons are very stable and are therefore unreactive. The elements that have a full valence shell are those in Group 18, called the ‘inert gases’ (e.g. the electron configurations of He: 2, Ne: 2,8, Ar: 2,8,8).
The periodic table can also be split into different blocks of elements that have similar physical properties, such as lustre, hardness, melting point and electrical conductivity. These blocks include metals, non-metals and metalloids, as shown in Figure 5.12.
The metals in the periodic table all have similar physical properties – for example, they are lustrous, have high melting points and conduct electricity. However, their chemical reactivity varies because each group has a different number of valence electrons.
The non-metals are a much smaller block of elements on the right-hand-side of the periodic table. They have similar physical properties – for example, they generally have low melting points and do not conduct electricity. Again, their chemical reactivity differs due to the different number of valence electrons in each group in the periodic table.
The metalloids are elements that have some properties of metals and some properties of non-metals. Because their chemical reactivity is more similar to that of non-metals, we will classify them here as non-metals.
The alkali metals (group 1) are the first group of the periodic table (see Figure 5.13). The elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr) are all alkali metals. Note that hydrogen is also in group 1, but is not considered an alkali metal because it is a non-metal. The alkali metals all have similar reactivity, because they all have one valence electron.
The alkali metals, including those you might observe in the classroom (sodium (Na) and potassium (K)), are relatively soft and can be cut with a knife. When they are cut open, they have a shiny appearance on the inside compared to their dull outer surface. This is because their outer surfaces readily react with oxygen in the air, forming dull metal oxides.
This reaction can be written as the following word equation and balanced chemical equation.
Na + O2 → 2
When placed in water, lithium, sodium and potassium will float, because they are less dense than water. Again, this is unlike most other metals you may have encountered.
All group 1 metals are highly reactive because they only have one valence electron. Elements are stable when they have a full outer shell of electrons, so group 1 metals readily react with other atoms and donate the one valence electron. When they do this, they form ions with a +1 charge.
Elements become more reactive as you go down a group. This is because as the atom gets larger, the one negatively charged valence electron becomes further from the attraction of the positively charged nucleus. The weaker attraction to the nucleus means the electron requires less energy or force to remove when colliding with other atoms. In fact, caesium can react explosively with substances such as water.
5.13 A piece of sodium metal that has been cut by a knife. It is shiny on the inside and dull on the outside.
Figure 5.15 A sodium atom. Having only one valence electron makes group 1 elements highly reactive.
Group 1 elements react readily with group 17 elements, forming white salts – one of these salts is the table salt that you put on your chips!
Word and balanced formula equations can be used to describe chemical reactions, and more on this topic will be covered in Chapter 6. The following word and balanced chemical equations show how sodium (Na) reacts with chlorine (Cℓ) to form table salt (sodium chloride, NaCℓ).
sodium + chlorine → sodium chloride 2 Na + Cℓ2 → 2 NaCℓ
To show how other alkali metals and group 17 elements react with each other, all you need to do is substitute their chemical names and symbols into the equations above.
Alkali metals are most famous for their reaction with water, and this is where they get their name. All group 1 metals react violently with water, producing hydrogen gas and an alkaline solution.
The word and balanced chemical equations show what happens when sodium reacts with water.
sodium + water → sodium hydroxide + hydrogen
2 Na + 2 H2O → 2 NaOH + H2
You can use these equations to predict what will happen when other alkali metals react with water.
Group 1 metals, such as sodium and potassium, are stored in jars of oil. When they come into contact with oxygen or water, these metals react, producing a lot of heat, an alkaline solution and hydrogen gas. This can often cause the metals to burst into flames. Due to this fire risk, group 1 metals are stored in oil, to protect them from oxygen and water vapours.
The reactivity of group 1 metals increases down the group, so don’t add caesium or francium to water!
1. State why group 1 metals are also known as alkali metals.
2. Describe why alkali metals form +1 ions when they react with other substances.
3. Write a word equation for lithium reacting with fluorine.
4. Explain why alkali metals are shiny on the inside and dull on the outside.
5. Identify whether the following statements are true or false. If false, give a reason why.
a) Alkali metals are more dense than water, so they float.
b) Alkali metals react with oxygen to form metal oxides.
c) Alkali metals are hard.
6. Other than an alkali, explain what other product is formed when alkali metals react with water.
7. Identify which metal is the most reactive in group 1.
Practical 5.2: Teacher demonstration
Aim
To determine the order of reactivity of two group 1 metals.
Materials
• sodium and potassium metals
• universal indicator
• large, thick-walled glass bowl
• scalpel
• white tile
• blotting paper
• tweezers
• safety screen
• disposable gloves
Method
1. Students should write a prediction in their books stating which they think will be the most reactive metal out of sodium and potassium.
2. Students should copy the results table into their science journal.
3. Half fill the large glass bowl with water and add a few drops of universal indicator until the colour can be seen throughout the liquid.
4. Using the tweezers, take a piece of sodium from its bottle and place it on the white tile.
5. Use the scalpel to cut off a small piece of the metal and observe the appearance of the metal on the inner and outer surfaces.
6. Making sure that all students are behind the safety screen, add the small piece of metal to the water and record your observations.
7. Repeat steps 4–6 with potassium.
Results
Table showing properties of sodium and potassium
Hard or soft
Sodium
Potassium
Discussion
Appearance when cut
More or less dense than water
Observations during reaction
1. Explain the decision to use tweezers rather than hands to pick up the metals.
2. Why was a safety screen necessary when conducting this experiment?
3. Describe the purpose of the universal indicator.
4. Describe any patterns, trends or relationships in your results.
5. Describe how you determined the reactivity of each of the metals investigated.
6. How did you determine whether the metals were more or less dense than water?
7. Explain how the reactivity of the metals changes as you go down group 1.
Conclusion
1. Propose a conclusion regarding the varying levels of reactivity of group 1 metals based on this experiment.
2. Support your statement by using the data you gathered.
Group 2 metals are also known as the alkaline earth metals. This group contains the elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). These elements all have two valence electrons.
The naturally occurring alkaline earth metals tend to be shiny and silvery-white in colour. Magnesium and calcium are abundant in Earth’s crust and are considered essential to all living organisms.
All group 2 elements are reactive, but not as reactive as group 1 elements. A group 2 element has an additional proton in the nucleus and therefore a stronger attractive force on its electrons, compared to group 1 elements in the same period. Group 2 elements therefore require more energy to remove the valence electrons. Group 2 elements form ions with a charge of +2 because they lose two electrons when they react.
Just like group 1 metals, alkaline earth metals react with oxygen to form metal oxides, and with group 17 elements to form metal salts. Table 5.3 shows the names and formulas of the products formed.
Element
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
Product formed when reacting with oxygen
Beryllium oxide
BeO
Magnesium oxide
MgO
Calcium oxide
CaO
1. List four of the alkaline earth metals.
Product formed from reacting with chlorine
Beryllium chloride
BeCℓ2
Magnesium chloride
MgCℓ2
Calcium chloride
CaCℓ2
2. State the charge that alkaline earth metals tend to form when they react.
Practical 5.3
Aim
To investigate the relationship between the position of a group 2 element in the periodic table and its reactivity with acid.
Prior understanding
Metals in group 2 of the periodic table are less reactive than those in group 1. This practical will determine the order of reactivity within group 2.
Recommended: Use a spreadsheet to analyse the data for this experiment and calculate uncertainty.
Useful formulas
Materials
Be careful
To reduce the risk of skin burn from acid:
• wear appropriate personal protective equipment
• wear safety glasses at all times
• wash your hands after the practical.
Change in volume (mL) = final volume (mL) − initial volume (mL)
Rate of gas produced (mL/min) = mean change in volume (mL) mean reaction time (min)
• 3 similarly sized samples of calcium (approximately 5 mm in diameter)
• 3 similarly sized samples of magnesium (approximately 5 mm in diameter)
• 30 mL hydrochloric acid (1 mol/L)
• 6 test tubes
• 10 mL measuring cylinder
• 100 mL measuring cylinder
• test-tube holder
Planning
• rubber stopper with glass tubing inserted through to fit the test tube
• rubber stopper to fit the 100 mL measuring cylinder
• 4 mm plastic tubing (minimum 30 cm)
• large bowl
• retort stand, bosshead and clamp
• stopwatch
• tweezers
1. Develop a hypothesis by predicting how a change in the periodic position of the group 2 metal will affect its reactivity.
2. Identify as many controlled variables as possible and describe how these will be managed to prevent any from affecting the measurements.
3. Complete a risk assessment for this practical, describing how any risks will be controlled.
Method
Part 1: Prepare the results table
Copy the results table into your science journal.
Part 2: Measure the reactivity of the first metal sample
1. Fill the large bowl with tap water.
2. Fill the 100 mL measuring cylinder with tap water.
3. Stopper the measuring cylinder using the rubber stopper (a complete seal will not be possible).
4. Invert the measuring cylinder into the large bowl (your teacher will show you how to do this if you are not sure) and clamp it in place with the stopper below the water line, as shown in Figure 5.19.
continued …
5. Remove the stopper from the measuring cylinder.
6. Attach the plastic tubing to the glass tubing on the rubber stopper. Place it beside the measuring cylinder for easy access later.
7. Measure 5 mL of 1 mol/L hydrochloric acid and pour into a test tube.
8. Using tweezers, add a piece of the first metal sample into the acid in the test tube. Be careful not to splash the acid.
9. Attach the rubber stopper with the plastic tubing to the test tube and position the end of the plastic tubing underneath the measuring cylinder so the gas can be collected.
10. Measure the initial volume of the gas in the inverted measuring cylinder and record in your table. Start the stopwatch.
11. After 5 minutes, record the final volume of the gas in the inverted measuring cylinder in your table.
12. Remove the rubber stopper and tubing from the test tube. Store the test tube and contents in the test-tube holder.
13. Repeat steps 7–12 with the other two samples of the first metal.
14. Remove the measuring cylinder and refill with tap water.
15. Stopper the measuring cylinder using the rubber stopper.
16. Invert the measuring cylinder into the large bowl and clamp it in place with the stopper below the water line.
17. Remove the stopper from the measuring cylinder.
Part 3: Measure the reactivity of the second metal sample
Repeat steps 7–12 from Part 2 with the samples of the second metal.
Results
Calculate the mean reaction rate for each metal sample
1. Calculate the change in gas volume for each trial and record it in the results table.
2. Calculate the rate of gas production in mL/min for each metal and record it in the results table.
3. Draw a scatterplot to analyse the relationship between the period number of each metal and its reaction rate.
4. Calculate the uncertainty for each metal.
5. Optional: Format the graph and insert a copy below the results table in your science journal.
Table showing rate of gas production by magnesium and calcium
Measurements
Period 2
Magnesium
Initial volume (mL)
Final volume (mL)
Change in volume (mL)
Rate of gas production (mL/min)
Period 3
Calcium
Trial 1 Trial 2 Trial 3
Mean rate of gas production (mL/min) Uncertainty of rate of gas production: max – min 2
Initial volume (mL)
Final volume (mL)
Change in volume (mL)
Rate of gas production (mL/min)
Discussion
1. Compare the mean rate of gas production for the different elements.
2. Predict the trend in reactivity for group 2 elements that are positioned lower on the periodic table.
3. Draw a conclusion as to how using different elements going down group 2 might affect the rate of gas production in reactions with acids.
4. Compare the uncertainties for each element. Which were the best results? Justify your answer with data.
5. Critique your management of the controlled variables. Were they managed properly to ensure they did not change and affect the measurements?
6. Could these results be used to predict reactivity trends in other groups on the periodic table? Explain your reasoning.
7. Suggest any changes that could be made to the method to improve the quality of the data in future experiments. Justify your suggestions by explaining how each change will improve the data quality.
Conclusion
1. Propose a valid conclusion that can be drawn from these results.
2. Justify this conclusion using data from your results.
3. Explain your conclusion using your own knowledge and research about group 2 metals.
4. State whether or not your hypothesis is supported.
Group 17 elements are known as the halogens. This group contains the elements fluorine (F), chlorine (Cℓ), bromine (Br) and iodine (I). Astatine (At) is also a halogen, but it is a rare radioactive element and will not be considered here. These elements all contain seven valence electrons.
halogens group 17 elements
The halogens form diatomic molecules, and their states and colours vary at room temperature. For example, fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. Table 5.4 lists some of the properties of these elements.
All group 17 elements have seven valence electrons. When they react with other substances, they gain an electron to make a full outer shell of eight electrons. This means they form ions with a charge of −1, or they share an electron with non-metal atoms to form a covalent bond.
As shown in Table 5.4, the reactivity of group 17 elements decreases as you move down the group. As the atom gets larger, the negatively charged valence electrons are further from the attraction of the positively charged nucleus. Thus making it more difficult for the nucleus to attract an additional electron.
FluorineF2 GasYellow−220−188
ChlorineCℓ2 GasGreenishyellow −101−35
BromineBr2 LiquidRed−7.258.8
Iodine I2 SolidGrey (purple in gas state) 114184
Reactivity increases up the group
1. Name three elements in group 17.
2. State the charge of a group 17 ion.
3. State one physical or chemical trend that can be observed as you go down group 17.
noble gases (group 18)
Group 18 elements are also known as the inert or noble gases. This group contains the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). These element all have a full valence shell of electrons.
The noble gases tend to be colourless, odourless and non-flammable. They have a full valence shell of electrons, which makes them very unreactive. Their applications include neon signs, medical imaging and radiotherapy to treat cancer.
Unlike the other groups we have discussed, noble gases are extremely unreactive because they have a full stable valence shell of electrons.
5.21 The first neon signs used neon gas, which produces an orange colour. Different elements, such as hydrogen and helium, are used to get different colours in modern neon signs.
Figure 5.22 A neon atom. Group 18 elements all have eight valence electrons and therefore a full outer shell.
The transition metals, lanthanoids and actinoids are all metallic elements that can be sorted into smaller special groups, as we have done for the alkali and alkaline earth metals. These groups of metals have variable chemical reactivity, but they are classed into groups because their reactive valence electrons are in similar shells. In Year 9, it is important that you know the names of these groups of metals, but you do not need to know their specific chemical reactivities.
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Section 5.2 review
Online quiz
Section questions
Remembering
1. State the group number of the following.
a) Alkaline earth metals
c) Noble gases
Teachers can assign tasks and track results
b) Halogens
d) Alkali metals
2. Recall what happens to the reactivity as you move down group 1.
3. Identify the following statements as true or false. If false, give a reason why.
a) All halogens are gases.
b) All alkali metals form hydrogen when they react with water.
c) Noble gases do not form ions.
d) Alkaline earth metals form ions with a +2 charge.
e) The general formula of a halogen molecule is X2
4. State how many valence electrons each of the following groups has.
a) Alkali metals
c) Halogens
b) Alkaline earth metals
d) Noble gases
5. A new element is discovered. It is shown to form an ion with a charge of +2. Identify which group it could belong to.
Understanding
6. Explain why group 2 elements are less reactive than group 1 elements.
7. Helium does not have eight valence electrons. Explain why it is still classified as a noble gas.
8. Explain why alkali metals are stored in oil or even sealed in inert gases.
Applying
9. Classify the following elements as alkali metals, alkaline earth metals, halogens or noble gases.
a) Magnesium
c) Sodium
e) Iodine
b) Argon
d) Potassium
10. Compare the properties and reactions of group 1 and 2 elements.
Analysing
11. Use examples provided in the text to construct a balanced chemical equation for the reaction between:
a) rubidium and water
b) lithium and oxygen.
12. Use Table 5.4 to predict some properties of astatine.
13. Predict the products of the following reactions.
a) Potassium and water
c) Calcium and oxygen
Evaluating
b) Magnesium and chlorine
d) Sodium and fluorine
14. Justify why group 18 was not present in Mendeleev’s periodic table.
15. Decide whether you would expect strontium to be chemically more similar to calcium or rubidium, giving reasons for your choice.
At the end of this section, I will be able to:
1. Name and write the formula of common covalent compounds.
2. Recall the charge of common elemental ions.
3. Write the name and formula of common ionic compounds.
In the last section you learned that elements have different chemical reactivities because of their different numbers of valence electrons. In general, atoms are most energetically stable when their valence shell is full. To do this, atoms must share valence electrons, to achieve what is called a stable octet (usually eight valence electrons). This is called the octet rule. When atoms share valence electrons, they create a chemical bond
Atoms share valence electrons in different ways. In this section, we will look at the sharing of electrons in covalent compounds and ionic compounds. The type of compound that is formed generally depends on whether the elements involved are metals or non-metals.
Because non-metal elements are closer to the right-hand side of the periodic table, they tend to have a valence shell that is closer to being filled with electrons than being empty. For example, fluorine has seven valence electrons – its electron configuration is 2,7. It needs only one electron to fill its valence shell and become 2,8. One way it can do this is to share an electron with another atom of fluorine, so that both have eight electrons in their valence shells (see Figure 5.24).
The pair of electrons being shared is called a bonding pair of electrons, and electrons are usually shared in this way between two non-metal elements. These bonds are also called covalent bonds. When two or more different non-metal elements combine with covalent bonds, the result is called a covalent compound. Non-metal compounds containing covalent bonds are also more commonly called molecules
The sharing of valence electrons in molecules is often shown on paper in a two-dimensional drawing. However, molecules exist in our three-dimensional world and therefore the sharing of valence electrons occurs in three dimensions. In fact, bonding pairs of electrons are areas of negative charge that repel each other. Therefore, covalent bonds tend to repel each other
an
(usually with eight electrons)
chemical bond the attraction between two atoms due to the sharing of their valence electrons bonding pair two valence electrons that are shared between two atoms covalent bond the formal sharing of a pair of valence electrons covalent compound a substance made up of two or more different nonmetal elements; a molecule molecule an element or a compound containing two or more atoms combined with covalent bonds; a covalent compound
so that the chemical bonds are as far apart from one another as possible in three dimensions. An example is the molecule methane, CH4, shown in Figure 5.25. The sketch of a methane molecule is in two dimensions. The ball-and-stick model shows that the covalent bonds between the carbon atom and the hydrogen atoms are actually 109.5° away from each other in three dimensions.
Figure 5.25 Two-dimensional and threedimensional models of methane, CH4
The names and formulas of some common covalent compounds are listed in Table 5.5. In Year 9, you need to learn this list, because these compounds will be referred to frequently in your future studies.
Table 5.5 Names and formulas of common covalent compounds
Acids in their pure form are also covalent compounds. The names and formulas of some common acids are listed in Table 5.6.
Table 5.6 Names and formulas of some common acids
1. Select from the list of words to complete the sentence below. metals, non-metals, metalloids Covalent molecules are formed when _____________ chemically bond with _____________.
2. Write the formula of the following molecules.
a) water
b) hydrochloric acid
Metal elements often have fewer valence electrons than non-metals. For example, the group 1 alkali element sodium has one valence electron, with the electron configuration 2,8,1. It would take too much energy for a sodium atom to share seven extra valence electrons or even gain seven extra electrons. The most energetically favourable way for an atom of sodium to achieve a stable octet is to lose its one valence electron.
If a sodium atom loses an electron, its new electron configuration will be 2,8 and it will have a full valence shell. However, its number of protons will now be one more than its number of electrons, and so it will be positively charged (Na+). This charged atom is called an ion, and a positively charged ion is called a cation. The lost electron must go somewhere, because it is unlikely to exist on its own.
Generally, a non-metal atom can gain lost electrons from cations to fill its valence shell. For example, fluorine has an electron configuration of 2,7 – it needs one electron to fill its valence shell. If it does gain an electron, it will have one more electron than its number of protons and it will be a negatively charged ion (F ), called an anion. Thus, sodium and fluorine can share valence electrons by sodium losing an electron and fluorine gaining an electron. The electrostatic attraction between the cation and the anion is called an ionic bond, and sodium fluoride (NaF) is called an ionic compound. Ionic compounds are usually formed when a metal element chemically bonds with a non-metal element.
Because we know the number of valence electrons that elements have from their electron configuration, we can predict how many electrons need to be lost or gained from an atom to achieve a stable octet. A simple rule to follow is to use the group number on the periodic table as a guide, as shown in Figure 5.27. Because the group 18 noble gases have a full valence shell, they do not need to form ions. Group 14 elements generally form covalent bonds rather than ionic bonds. For example, nitrogen is in group 15 and therefore it should form the N3− ion, because it needs three electrons to fill its valence shell.
cation a positively charged ion anion a negatively charged ion ionic bond an electrostatic attraction between a cation and an anion ionic compound two or more different ions attracted by a strong electrostatic force
Figure 4.26 A positively charged ion (a cation) bonds with a negatively charged ion (an anion) through the loss and addition of electrons.
Figure 5.27 Periodic table showing the main elements in each group and the charges of the ions formed by atoms of these elements when they lose or gain electrons. Note that groups 14 and 18 typically do not form ions.
1. Use the periodic table to identify the formula of the ion formed by the following elements.
a) O
b) S
c) Mg
d) Li
e) Br
Table 5.7 shows all elemental ions that you should be able to use in Year 9. This list also shows some ions that cannot be easily identified from the periodic table.
ElementIon
caesium caesium Cs+
copper copper(I) Cu+ copper(II) Cu2+
hydrogen hydrogen H+
lithium lithium Li+
potassiumpotassium K+ rubidium rubidium Rb+
silver silver Ag+
sodium sodium Na+
barium barium Ba2+
calcium calcium Ca2+
cobalt cobalt(II) Co2+
iron iron(II) Fe2+ iron(III) Fe3+
lead lead(II) Pb2+
magnesiummagnesium Mg2+
manganesemanganese(II) Mn2+
nickel nickel(II) Ni2+
strontium strontium Sr2+
zinc zinc Zn2+
aluminiumaluminium Aℓ3+ chromium chromium(III) Cr3+
bromine bromide Br
chlorine chloride Cℓ fluorine fluoride F iodine iodide I
oxygen oxide O2−
sulfur sulfide S2− nitrogen nitride N3−
Table 5.7 Common elements and the ions they form
The transition metals can sometimes have more than one preferred cation charge. These different ions can also produce unique coloured solutions. Iron and copper are two examples (see Table 5.7).
Use the Internet to research why roman numerals are used in the name of some transition metal ions. What is the maximum roman numeral that could be used?
Quick check 5.10
1. Write the formula of the following ions.
a) aluminium
b) oxide
c) bromide
d) iron(II)
The naming of ionic compounds follows a set of rules and involves naming the elemental cation and elemental anion present.
The rules for naming ionic compounds are listed in Table 5.8.
Step
Explanation
1The name of the cation is placed first in the name, and it is the same as the name of the element.
2The name of the anion is placed second. The end of the element name is changed to '-ide'. These are the same names as those in Table 5.7.
3The cation and anion names are placed in order with a space between them.
Table 5.8 Rules for naming ionic compounds
Quick check 5.11
Example
lithium (Li+) lead(II) (Pb2+)
fluorine → fluoride (F ) oxygen → oxide (O2−) nitrogen → nitride (N3−)
lithium chloride lead(II) oxide
1. Write the names of the following ionic compounds from their formulas.
a) NaBr
b) CaS
c) Aℓ2O3
d) SrF2
The positive and negative charges of cations and anions in an ionic compound must cancel out, because the ionic compound is neutral overall. Therefore, when writing the formula of an ionic compound, you need to account for the overall charge by adding ions to balance the charge. For example, the ionic compound magnesium chloride is made up of Mg2+ and Cℓ ions. If we simply place these ions together (i.e. MgCℓ), the formula will be incorrect because the overall charge would be +1. In order to cancel out the Mg2+ charge, two Cℓ ions are required. This is shown using a subscript ‘2’ in the formula: MgCℓ2.
In some cases, identifying the number of each ion is challenging, so another process for writing ionic formulas is shown in Worked example 5.1.
Worked example 5.1
Write the formula for magnesium chloride and magnesium sulfide. Working
Mg2+
(It is a group 2 metal.)
Cℓ
(It is a group 16 non-metal.)
Mg2+ Cℓ
Already in its simplest form. Mg1 Cℓ2
Mg2+
(It is a group 2 metal.) S2− (It is a group 17 non-metal.)
MgCℓ2 MgS
Step 1. Write the symbol of the elemental ion.
Step 2. 'Drop and swap' the superscript coefficients and remove the charge signs.
Step 3. Simplify to the lowest whole-number ratio.
Step 4. Combine the elements and remove any coefficients of 1.
Figure 5.29 Chemical names and formulas are shown on all chemical bottles, vials and barrels so that chemists know exactly what is present.
Quick check 5.12
1. Write the formulas for the following ionic compounds from their names.
The formulas of ionic compounds show the simplest whole-number ratio between cations and anions, but this is not the actual number of each ion in the compounds (in covalent molecules, it is). Ionically bonded substances exist in a giant three-dimensional lattice of repeating cations and anions. The ionic formula only shows the simplest ratio of elements. For example, the compound sodium chloride, NaCℓ, doesn't actually contain one sodium and one chloride ion; it is millions of ions in a three-dimensional cubic lattice.
and more!
Section 5.3 questions
Remembering
1. Recall the formulas for the following molecules. a) Carbon dioxide b) Hydrogen c) Ozone d) Water
2. Recall the names of the following acids. a) Oxygen b) Nitrogen c) Chlorine d) Ozone
Understanding
3. Identify the formulas of the following ions. a) Chloride b) Oxide c) Aluminium d) Magnesium
4. Identify the names of the following ions. a) Cu2+ b) Fe3+ c) Sr2+ d) N3–
Applying
5. From the following list of substances, determine the covalent molecule. carbon monoxide, sodium chloride, chromium(III) oxide, barium bromide
6. Write the formulas of the following ionic compounds. a) Nickel(II) sulfide b) Calcium fluoride c) Potassium oxide
Analysing
7. Write the names of the following compounds and state whether they are covalently or ionically bonded. a) CuI b) CO c) CH3COOH d) Na3N
Evaluating
8. Write the formulas of the following compounds and state whether they are covalently or ionically bonded.
a) Methane b) Ammonia c) Rubidium sulfide d) Lithium chloride
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Chapter checklist
Success criteria Linked questions
5.1I can describe how Mendeleev arranged elements in his early periodic table. 9, 16
5.2I can describe the structure of the periodic table in terms of groups and periods, and blocks of metals, metalloids and non-metals. 1, 2
5.2I can identify the transition metals, lanthanoids and actinoids on the periodic table. 3, 5
5.2I can determine the electron configuration of different elements.8, 11
5.3I can describe how valence electrons are shared in ionic bonding and covalent bonding. 12
5.3I can write the names and formulas of common covalent and ionic compounds. 10, 15
Scorcher competition
Review questions
Data questions
Review questions
Remembering
1. State the group and period of the following elements.
a) Boron (B)
b) Titanium (Ti)
c) Platinum (Pt)
d) Strontium (Sr)
2. State the group number of the following elements.
a) An element with the electronic configuration 2,8,1
b) An element with 18 electrons
c) A halogen
d) A noble gas
3. Identify each of the following elements as a transition metal, lanthanoid or actinoid.
a) Europium (Eu)
b) Rhenium (Re)
c) Uranium (U)
4. Magnesium and beryllium are in group 2. Recall the other name given to elements in group 2.
5. Identify the names and positions of three elements that are transition metals.
6. State why elements are placed together in the same group.
Understanding
7. Describe the position of metals and non-metals on the periodic table.
8. Write the electron configuration for a sulfur atom.
9. Explain why Mendeleev left gaps in his periodic table.
10. Write the chemical formula for:
a) lithium oxide
b) carbon monoxide
c) iron(II) chloride.
Applying
11. State how many valence electrons a carbon atom has.
12. Compare ionic and covalent bonding by completing this table.
Bond is between ___ and ___ How is the bond formed?
13. Decide whether zinc iodide is an ionic compound or a covalent compound.
Analysing
14. Figure 5.31 shows an ammonia molecule. Ammonia is a gas at room temperature and has the chemical formula NH3 Infer what type of chemical bond exists between the nitrogen and hydrogen atoms.
15. Write the name of the following compounds.
a) CH4
b) NH3
c) Na2S
Evaluating
16. A unknown element:
• reacts violently with water
• feels soft
• has an electron configuration of 2,8,8,1. Given those properties, determine which group it belongs to. Give reasons for your choice.
17. Determine the relationship between an element’s atomic number, its number of electrons and its position in the periodic table.
18. Use the melting point data below to predict the physical states (solid, liquid or gas) of the unknown elements at room temperature. Note that room temperature is around 25°C.
Carbon dioxide (CO2) is a covalent compound that is produced in the combustion of fuels. As the human population has grown over time, fuel consumption has steadily increased around the world to meet the growing demand for energy. As a result, the carbon dioxide emitted into the atmosphere has also been steadily increasing. Figure 5.32 shows the average CO2 concentration in the atmosphere in parts per million (ppm) each year from 1960 to 2024.
Figure 5.33 shows atmospheric ozone (O3) concentration, in Dobson units. One Dobson unit is equivalent to the total volume of ozone in the atmosphere being placed in a vertical column at 0°C and 100 kPa, forming a layer 0.01 mm thick.
Figure 5.32 Average CO2 concentration in the atmosphere, 1960–2024
Figure 5.33 Atmospheric ozone concentration, 1980–2020
The following questions refer to Figure 5.32.
1. Identify the concentration of CO2 in the atmosphere in 1995.
2. Determine the year when the concentration of CO2 reached 410 ppm.
3. Identify the trend in the graph of atmospheric CO2
A. positive linear
B. negative linear
C. positive exponential
D. negative exponential
4. State in which decade(s) the rise in CO2 concentration was more than 20 ppm.
5. Predict the concentration of carbon dioxide that will be present in the atmosphere in the year 2030.
The following questions refer to Figure 5.33.
6. Identify whether atmospheric ozone has generally been depleted or replenished between 1980 and 2020.
7. Calculate the thickness of the total atmospheric ozone content in 2020, given the Dobson units = 276.
The following question refers to Figures 5.32 and 5.33.
8. Compare the trends in atmospheric CO2 and O3 over the decades shown in the graphs and decide whether these trends are related.
Salinity is the presence of dissolved ionic salts in water sources. Knowing the level of salinity is important in various fields of science, including: monitoring the water quality of natural water sources, such as rivers and lakes or marine ecosystems; identifying salt concentrations in agricultural soils; and even understanding the impact of dissolved salts in ocean waters on the coastal corrosion of ships and other metallic structures.
The magnitude of salinity can be measured using the electrical conductivity of the saline water. The higher the number of ions dissolved in water, the higher the electrical conductivity of the solution.
Create a working circuit that can measure the conductivity of saline solutions, such as water from oceans, rivers or lakes.
In groups of two to three, design and construct a circuit that can be used to measure the electrical conductivity of saline water.
• graphite electrodes
• beaker
• wires
• multimeter
• power supply
1. Research the types of circuits and cells that can be constructed to measure the electrical conductivity of solutions.
2. Conduct some research on the units of measurement usually quoted for electrical conductivity, and consider how you might record your data in this way.
3. Identify what the expected electrical conductivity range of ocean/river/lake water would be.
1. Design your experimental set-up.
2. Consider the volume of water that would be required for the investigation.
Create
1. Construct your circuit.
2. Follow the method that you have chosen to record the electrical conductivity of your chosen water source.
1. Did the experiment provide the expected results? If not, discuss why.
2. Would the experiment give the same result for a smaller or larger volume of the water source? Consider ways in which the experiment could be amended to account for this question.
3. Evaluate the reliability of your collected data and compare it to values given in the literature.
Introduction
Chemical reactions occur when atoms in reactants are rearranged, resulting in the formation of new products. The law of conservation of mass states that mass cannot be created or destroyed during a chemical reaction. This law is crucial for chemical manufacturers because it allows them to predict and plan efficient chemical syntheses. In this chapter you will learn about some chemical reactions used in the mining industry to purify metals, as well as how scientists can prepare useful gases such as hydrogen, oxygen and carbon dioxide.
Evidence of chemical change can be indicated by:
• Light production
• Sound production
• Colour change
• Temperature change
• Change in physical properties
• Gas production
Section 6.1
Section 6.2
Section 6.3
Gases commonly produced in the laboratory:
• Hydrogen
• Oxygen
• Carbon dioxide
Chemical reactions
Reactants → products
Balancing equations
Demonstrates that Written as equations
Chemical reactions obey the law of conservation of mass.
Applications of chemical reactions
Extracting metals:
• Reaction with carbon
• Electrolysis
Reactivity of metals
Curriculum content
Chemical sciences
Chemical reactions involve rearranging atoms to form new substances; word and balanced chemical equations can be used to represent the rearrangement of atoms in a chemical reaction and demonstrate the law of conservation of mass
• demonstrating the law of conservation of mass to model the balancing of chemical equations
• experimentally
• using molecular modelling kits, diagrams or simulations
• writing word equations and balanced chemical equations to demonstrate the law of conservation of mass when provided with the chemical formulae for reactants and products
• writing word equations and balanced chemical equations for chemical reactions observed in practical activities, such as the production of oxygen, carbon dioxide and hydrogen gas and reactivity of metals
© School Curriculum and Standards Authority
balanced catalyst chemical change coefficient effervescence electrolysis law of conservation of mass native metal product reactant reaction conditions rearrange
At the end of this section, I will be able to:
1. Recall the evidence of chemical change.
2. Label reactants and products in a chemical equation.
Many areas of modern life require chemical reactions. The components of a lunchtime sandwich, the ink in a pen and the screen of a smartphone have all been carefully produced using chemical reactants.
The easiest way to describe a chemical reaction is that starting substances are converted into new substances, but of course it is not as simple as that. During chemical reactions, the atoms in the starting substances are rearranged to make new substances. For this to happen, chemical bonds holding the atoms together in the starting substances must be broken and new bonds must form in different arrangements to make the new substances.
Figure 6.2 shows a chemical reaction in which compound AB reacts with element C to make a new compound, BC, and element A. In this reaction, the bond between A and B in compound AB is broken and a new bond is formed between B and C to form compound BC – the atoms have been rearranged. The new substances are different from the starting substances; therefore, a chemical reaction has taken place. The arrow in the chemical reaction separates the starting substances that react together from the new substances produced by the reaction. The arrow indicates that a chemical reaction is occurring and is normally said aloud as ‘yields’. A chemical equation does not have an equals sign.
Let’s look at a real-life example. Figure 6.3 shows the chemical reaction between carbon and oxygen. In this chemical reaction, the bond between the two oxygen atoms is broken, the atoms are rearranged, and new bonds are formed between each oxygen atom and the carbon atom. The new substance formed is called carbon dioxide.
The rearrangement of the atoms can affect the properties of the substances in chemical reactions. Carbon is a solid at room temperature and oxygen is a gas. The compound formed in this reaction, carbon dioxide, is a gas at room temperature. The arrangement of the atoms in a compound influences the physical properties of a substance, which is why the physical properties of the compound formed in Figure 6.3 are so different from the starting substances.
1. Explain how new substances are formed during a chemical reaction.
2. Describe what is happening to the substances in the following equation.
Making thinking visible 6.1
Think: What do you already know about how atoms rearrange in chemical reactions?
Puzzle: What questions do you have that puzzle you about the rearrangement of atoms in chemical reactions?
Explore: Conduct some research on how the rearrangement of atoms can be demonstrated in word equations and balanced chemical equations.
Scientists represent chemical structures and reactions in a variety of ways.
The difference in physical properties between the starting and new substances is one piece of evidence that a chemical reaction has occurred, but there are other ways in which this can be observed. In Year 8 you learned about the differences between a physical and a chemical change Table 6.1 lists some observable evidence of a chemical reaction. A chemical change occurs when chemical species react to form new chemical species with different chemical compositions or arrangement of atoms. In contrast, a physical change involves a change in size, shape or state of matter without any alteration in the chemical composition. While both types of changes can be reversible, some chemical changes require a significant amount of energy to reverse, making them relatively ‘irreversible’ in practical terms. In contrast, physical changes, such as the boiling and freezing of water, are usually easily reversible.
Indicator
Example
Sound producedChemical reactions that occur explosively are usually accompanied by a loud bang.
Change in colourA grey-coloured iron bolt reacting with oxygen and water forms red rust (iron(III) oxide).
Change in physical properties
Sodium (a soft metal) reacting with water (a colourless liquid) produces sodium hydroxide (a colourless solution) and hydrogen gas, which is visible as rapid bubbling, also referred to as effervescence
Light producedThe production of fire is a chemical reaction called combustion, which involves the rapid oxidation of a fuel in the presence of heat and oxygen, producing heat, light and by-products such as smoke and ash.
Change in temperature
Magnesium metal reacting with an acid releases heat, which can be measured with a thermometer.
effervescence bubbles or fizzing in solution
reactant a substance that reacts in a chemical reaction product a substance that is formed in a chemical reaction catalyst a chemical that speeds up a chemical reaction; it is not a reactant and is not used up during the reaction reaction conditions the conditions required for a chemical reaction to proceed
1. Recall examples of a chemical change.
2. ‘All chemical changes are irreversible.’ Propose whether this statement is true or false and explain your answer.
3. When a pan of water is heated on a cooker top, the water turns into steam. When the steam hits a cold window, it condenses back into liquid water. Identify whether this is an example of physical change, chemical change or both.
In a chemical reaction, substances react with each other to form new substances. The substances doing the reacting are called reactants. Reactants are always written on the left-hand side of a chemical equation (before the arrow). The new substances that are formed are called products Products are always written on the right-hand side of an equation (after the arrow). Figure 6.6 shows a word equation for the reaction between magnesium and hydrochloric acid. A word equation shows the reactants and the products written in words with an arrow to represent the chemical change.
Magnesium and hydrochloric acid are reactants, so they are written on the left-hand side of the arrow. Magnesium chloride and hydrogen are products, so they are written on the right-hand side of the arrow. The arrow denotes that a chemical change has occurred.
Not all chemical reactions happen spontaneously (that is, without us having to do anything to them). Some reactions require heat or light energy to get started, some require high pressures, some need a chemical called a catalyst to speed up the reaction. Some reactions do happen spontaneously, but over a longer period of time. These factors are called reaction conditions. When special reaction conditions are required, they are written above (or below) the arrow in a chemical equation. This shows that these conditions are required for the reaction to proceed, but they are not directly involved in the reaction (Figure 6.7b).
1. Identify which side of a chemical equation the reactants and the products are written on.
2. Identify where the reaction conditions should be written in a chemical equation.
Did you know? 6.1
the perfect soufflé
A soufflé is a French sweet or savoury dish made with beaten egg whites. Its name comes from the French word souffler, which means ‘to puff’ in English. A well-prepared soufflé uses chemical reactions in cooking the base mixture at approximately 190°C to produce gases that help to ‘puff’ the mixture. If the temperature is too high or the mixture is cooked for too long, the gas can escape the soufflé, causing it to irreversibly collapse. A collapsed soufflé is certainly a French culinary faux pas!
Chemical equations can be represented in different ways. Word equations show the names of the reactants and products, while formula equations show the chemical formulas of the reactants and products. Chemical reactions can also be represented using chemical structures (as shown for caffeine in Figure 6.9), which give shape and chemical bonding structure information; however, you will not use this type of representation in Year 9. Regardless of the type of chemical equation used, there is always an arrow separating the reactants on the left and the products on the right. The different types of equations only differ in the way the reactants and products are represented.
more information about its chemical bonding.
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Section 6.1 review
Online quiz
Section 6.1 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. State what ‘→’ means in a chemical reaction.
2. Name the reactants in the following reactions.
a) sodium hydroxide + iron carbonate → iron hydroxide + sodium carbonate
b) propane + oxygen → carbon dioxide + water
c) hydrogen + oxygen → water
d) calcium carbonate → calcium oxide + carbon dioxide
3. Name the products of each of the reactions in Question 2.
Understanding
4. Select the correct definition for each keyword.
Keyword Definition
Reactants The substances formed in a chemical reaction
Products The type of environment that the reaction needs for it to happen, e.g. temperature or pressure
Reaction conditionsThe substances that are reacting in a chemical reaction
5. Describe what happens to the atoms in reactants during a chemical reaction.
Applying
6. Compare physical changes and chemical changes.
7. Nitrogen and oxygen gas exist in the atmosphere, but they do not react together. However, at the high temperatures and pressures in car engines, they will react with each other. Identify the reaction conditions needed to cause nitrogen and oxygen to react with each other.
Analysing
8. Categorise the following examples as physical change or chemical change.
a) Sugar dissolving in a cup of tea
b) Iron nail rusting
c) Ice melting to form water
d) Frying an egg
e) Toasting bread
Evaluating
9. The following equation shows what happens during respiration, in which glucose and oxygen (reactants) react to make carbon dioxide and water (products). Deduce the three mistakes that have been made and rewrite the equation correctly. carbon dioxide and water = glucose + oxygen
Learning goals
At the end of this section, I will be able to:
1. Define the ‘law of conservation of mass’.
One of the fundamental laws of chemistry is the law of conservation of mass. This law states that matter can be neither created nor destroyed in chemical reactions.
phlogiston theory and the discovery of oxygen
2. Interpret a word equation and a balanced chemical equation for a chemical reaction. law of conservation of mass a scientific law that states that matter can be neither created nor destroyed
In the late 1700s, a theoretical element called phlogiston (from the Greek phlox, which means ’flame’) was attributed to the flame produced during a combustion reaction. In 1774, scientist Joseph Priestley shone a beam of sunlight directly at a substance called ‘red precipitate’ (mercury(II) oxide), which he considered to contain a large amount of phlogiston. As the red precipitate decomposed, it lost mass and Priestley collected a gas that was produced, which he called ‘dephlogisticated air’ (oxygen gas).
Priestley found that a candle burned longer and a mouse lived longer in the presence of the new type of air. Not only did Priestley make the first discovery of oxygen gas, but he had also built a foundation for the discovery of the law of conservation of mass that would come a decade later.
In the late 1700s, scientists thought that for something to burn, it had to contain the element phlogiston (see Science inquiry 6.1).
Antoine Lavoisier, a French scientist, burned red precipitate (mercury(II) oxide) in a closed environment, meaning that no substances could escape, and noticed that the mass of the substances at the end was the same as the mass of the substances at the start. In 1789, he called this Lavoisier’s law – it was later renamed the law of conservation of mass.
The law of conservation of mass states that matter cannot be created or destroyed – but what does this mean? Take the mass of all the ingredients used to make a batch of pancakes (flour, eggs and milk). When the pancakes have been cooked, the mass of all the pancakes made from the batter should equal the mass of the starting ingredients. This means that no matter has been created or destroyed. However, because this is not a closed environment, there might be a difference between the two masses, because water evaporates from the batter during the cooking, making it seem as though matter has been lost.
If you leave a full glass of water outside on a hot day for long enough, it will become half full. The glass of water now has a smaller mass. You may conclude that mass has been lost. But this is not the case. The water heats up, forming water vapour, which leaves the glass and goes into the air. Water vapour has mass. The water vapour has left the glass, which is why the mass of the water in the glass decreases, but the water is still present in the air somewhere. This example demonstrates why it is important to observe the conservation of mass in a closed system (one in which nothing can escape). In an open system, reactions that produce gases will appear to lose mass.
Quick check 6.4
1. Identify who discovered the law of conservation of mass.
2. Define the law of conservation of mass.
3. If the mass of reactants is 30 g, state what the mass of the products will be.
4. Discuss why it is difficult to observe the law of conservation of mass in an open system.
5. Explain why the mass of a glass of water left out on a hot day decreases.
As a scientist, you need to factor in the law of conservation of mass when you write chemical equations. Consider the reaction in Figure 6.14. Copper(II) chloride (CuC2) is being broken down into its elements: copper (Cu) and chlorine (Cℓ2).
Figure 6.14 A particle representation and chemical equation showing the decomposition of copper (II) chloride into
For this reaction to obey the law of conservation of mass, there must be the same number of atoms of each element in the reactant and the products. In the reactants, there is one atom of copper and two atoms of chlorine. In the products, there is one atom of copper and two atoms of chlorine. The number of atoms is the same on each side of the equation and therefore the mass is also the same. The only difference is in how the atoms are arranged.
Figure 6.15 shows a particle representation and chemical equation for the reaction between magnesium (Mg) and oxygen (O2) to form magnesium oxide (MgO).
Figure 6.15 The reaction between magnesium and oxygen forms magnesium oxide.
The number of each type of atom in the reactants and the product is different. This means that the equation in Figure 6.15 does not obey the law of conservation of mass. There is one magnesium atom on each side of the arrow, but the left-hand side of the equation has two oxygen atoms while the right-hand side has only one. This shows the product as having less mass than the reactants, which cannot happen. Therefore, the chemical equation must be altered so that the law of conservation of mass is observed.
Figure 6.16 shows the equation adjusted so that it has two oxygen atoms on the right-hand side. This was done by adding another unit of magnesium oxide to the products. However, adding the extra magnesium oxide unit to balance the oxygen atoms has also added another magnesium atom. The magnesium atoms are now unbalanced, with one on the left-hand side and two on the right-hand side of the equation.
Adding one more magnesium atom to the left-hand side (reactants) makes the equation balanced (see Figure 6.17). Each side of the equation now has two magnesium atoms and two oxygen atoms. The numbers added to balance a chemical equation are called coefficients
To show that a chemical equation obeys the law of conservation of mass, a balanced chemical equation provides more information than a word equation because the number of reactant and product atoms are shown.
Quick check 6.5
1. Explain why it is necessary to balance equations.
Figure 6.16 This equation now has the correct number of oxygen atoms, but it is still not observing the law of conservation of mass.
Figure 6.17 The correct balanced equation has the same number of each atom in the reactants and products and therefore observes the law of conservation of mass.
balanced when a chemical equation has an equal number of atoms of each element on both the reactant and the product sides of the equation coefficient a number placed in front of a chemical symbol to balance a chemical equation
2. Two students were doing an experiment in the laboratory. They measured the mass of reactants as 50 g. After the reaction had completed, the mass of the products was 34 g. They noticed that a gas was given off during the reaction, so they wanted to find out the mass of this gas. Explain to the students how they could calculate this.
Practical 6.1
observing the law of conservation of mass (1)
Aim
To observe the law of conservation of mass by reacting magnesium and oxygen
Materials
• small piece of magnesium ribbon
• tongs
• crucible
• matches
• Bunsen burner
Method
1. Copy the results table in the Results section.
• clay triangle
• tripod
Be careful
Do not stare directly at combusting magnesium.
• heatproof mat
• safety glasses
2. Set up a Bunsen burner on a heatproof mat. Place the clay triangle on top of the tripod.
3. Weigh the crucible with its lid.
4. Place a piece of magnesium ribbon in the crucible and weigh it again with the lid on.
5. Calculate the mass of magnesium by subtracting the mass of the empty crucible.
6. Heat the crucible over the Bunsen burner on the blue flame, carefully lifting the lid using the tongs to allow sufficient air into the crucible.
7. Continue heating until the magnesium has fully reacted.
8. When the crucible has cooled sufficiently, weigh it and its contents again. Calculate the mass of the new compound by subtracting the mass of the empty crucible.
Results
Copy and complete the following table.
Table showing mass of crucible and its contents before and after heating
Item
Crucible + lid
Crucible + lid + magnesium before heating
Crucible + lid + compound after heating
Magnesium
Compound
Discussion
Mass (g)
1. Describe your observations when the magnesium reacted in the crucible. How did you know that a chemical change had occurred?
2. The formula for oxygen is O2. Write a balanced chemical equation for this reaction.
3. State whether your results demonstrate the law of conservation of mass.
4. Explain why this reaction is a difficult example for showing the law of conservation of mass.
5. Propose how you could have made it easier to demonstrate the law of conservation of mass.
6. Identify any potential sources of error in this experiment.
7. Suggest any changes that could be made to the method to improve the quality of the data in future experiments. Justify your suggestions by explaining how each change will improve the data quality
observing the law of conservation of mass (2)
Aim
To observe the law of conservation of mass by reacting vinegar and baking soda
Materials
• 10 mL vinegar (ethanoic acid)
• 5 g baking soda
• balance
• small measuring cylinder
• small conical flask
• resealable plastic bag (big enough to fit 10 mL of vinegar and 5 g of baking soda, and with enough space for you to manipulate their containers)
Method
1. Copy the results table in the Results section.
2. Pour 10 mL of vinegar into the measuring cylinder.
3. Weigh out 5 g of baking soda into the conical flask.
4. Put the measuring cylinder and conical flask into the plastic bag. Do not spill any of the contents of the measuring cylinder or conical flask.
5. Measure the mass of the measuring cylinder, conical flask and plastic bag, using the balance. Record this in your results table.
6. Seal the plastic bag again, being careful not to spill any of the contents.
7. Without opening the bag, pour the vinegar into the conical flask containing the baking soda.
8. When you think the chemical reaction has finished, record the mass of the contents without opening the bag. Record this in your results table.
9. Calculate the change in mass using the initial mass and final mass results. Record these in your results table.
Results
Copy and complete the following table.
Table showing mass of contents before and after reaction
Initial mass (g)
Final mass (g)
Change in mass (g)
Discussion
1. Describe your observations when the vinegar and baking soda reacted in the plastic bag. How did you know that a chemical change had occurred?
2. The gas produced in the reaction is the same as one of the gases you breathe out. What is the name and for mula of this gas?
3. When vinegar (ethanoic acid) reacts with baking soda (sodium bicarbonate), sodium ethanoate, water and carbon dioxide are produced. Write a word equation for this reaction.
4. This experiment was carried out in a closed system. Deduce what you think this means.
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Section 6.2 review
Online quiz
Section 6.2 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Recall the law of conservation of mass.
2. In a chemical reaction, there are two reactants and one product. The mass of the product is 30 g. The mass of the first reactant is 17 g. Demonstrate that the mass of the second reactant must equal 13 g to obey the law of conservation of mass.
3. Identify the mass of the products when the following react to completion.
a) 35 g of reactants
b) 12 g of reactants
c) 2 g of one reactant added to 24 g of another reactant
d) 6 g of one reactant added to 3 g of another reactant
Understanding
4. Emma carried out an experiment by reacting different amounts of magnesium with oxygen. Her measurements are shown in the following results table. Explain how her results support the law of conservation of mass.
Applying
5. Analyse the following chemical equations to find which ones obey the law of conservation of mass. For those that do not obey the law of conservation of mass, balance the equations.
a) C + O2 → CO2
c) H2 + O2 → H2O
e) Ba + O2 → BaO
Analysis
b) CaCO3 → CaO + CO2
d) Na + Cℓ2 → NaCℓ
6. Distinguish between an open system and a closed system.
Evaluating
7. Decide whether an open system or a closed system is better for observing the law of conservation of mass. Justify your choice.
8. In a chemical reaction, the mass of the reactants was 15 g. The mass of the products was 12 g. Decide whether this reaction followed the law of conservation of mass. Justify your choice.
9. Joy and Paul leave a glass of water on their balcony. By the time they realise it has been left there, the volume of water in the glass has reduced. Joy says that the mass of water molecules has been lost. Paul says there is less water and therefore less mass in the glass because the water has evaporated, and this mass has been added to the mass of the air.
a) Decide who you think is correct and justify your reasoning.
b) Develop an experiment to prove who was correct.
Learning goals
At the end of this section, I will be able to:
1. Describe the reaction of metals with carbon and electrolysis.
2. Explain how the gases hydrogen, oxygen and carbon dioxide are prepared.
Chemical reactions produce a range of naturally occurring chemical compounds. Industrial chemical manufacturers often take such compounds and use chemical reactions to re-form pure elements. This is a major industry in Australia, particularly in mining, in which metal compounds are mined and reacted to re-form pure metals.
extracting metals
Because most metals in their elemental states are reactive, many of them are found naturally as compounds, known as ores. Ores contain metal atoms as chemical compounds mixed with other impure substances. Some very unreactive metals may be found in the native elemental state.
Metals can be ranked from those observed to be most reactive to those observed to be least reactive. This list is called the reactivity series.
Potassium (K)
Sodium (Na)
Calcium (Ca)
Magnesium (Mg)
Aluminium (Aℓ)
Zinc (Zn)
Iron (Fe)
Nickel (Ni)
Tin (Sn)
Lead (Pb)
Copper (Cu)
Silver (Ag)
Gold (Au)
Generally, more reactive metals are more likely to react and form ionic compounds naturally than less reactive metals.
Metals that are very unreactive and can be found in the earth in the elemental form are known as native metals. For example, gold, silver and copper (see Figure 6.18) metals can be found in their elemental form.
Most relatively reactive metals have reacted with oxygen or sulfur to form metal oxide or sulfide mineral ores. The elemental form of the metal can be synthesised by reacting the metal oxides or sulfides with carbon (such as coal) at extremely high temperatures in a blast furnace – the carbon removes the oxygen from the metal ore, producing carbon dioxide and the pure form of the metal. The reaction below is an example of this form of extraction.
Practical 6.3
extracting iron using a matchstick
Aim
To extract iron from iron oxide
Materials
• iron(III) oxide powder
• sodium carbonate powder
• 100 mL beaker filled with water
• watchglasses
• crucible tongs
• weighing boat
Method
1. Copy the table shown in the results section.
• spatula
Be careful
Wear appropriate personal protective equipment.
• Bunsen burner
• bench mat
• magnet
• safety match
• cling wrap
2. Run the magnet over the iron(III) oxide powder, sodium carbonate powder and match head. Record whether they are magnetic.
3. Moisten the head of the match by dipping it into a beaker of water.
4. Place a small amount of sodium carbonate powder in a watchglass. Do the same with the iron(III) oxide powder.
5. Roll the head of the match in the sodium carbonate powder and then in the iron(III) oxide powder.
6. Using the pair of tongs, hold the head of the match in a blue Bunsen burner flame – only let it burn halfway down the match.
7. Allow the match to cool.
8. Use the spatula to crush the charred head of the match into the weighing boat.
9. Run the magnet underneath the weighing boat and record what you see. Wrap the magnet in cling wrap, so it can be directly dipped into the match remains.
Results
Copy and complete the table.
Table showing results of test for magnetism before and after reaction
Substance
Iron(III) oxide powder
Sodium carbonate powder
Match head (before heating)
Charred remains (after heating)
Discussion
Magnetic?
1. In this experiment, you reacted iron(III) oxide powder with carbon to try to extract the metal. Which chemical did the carbon come from?
2. How did you know that iron metal was the product formed?
3. Write a word equation for the reaction studied.
electrolysis a process in which an electric current is used to decompose a chemical compound
Some of the most reactive metals require a lot of energy to be converted back to their elemental form. To extract these metals, an electric current is passed through a molten (liquid) form of the impure metal, resulting in the extraction of the pure form of the metal, in a method called electrolysis. Because this process is expensive, it is only used to extract reactive metals such as aluminium, sodium and potassium.
Green hydrogen fuel stations that are being constructed across Australia store high-pressure hydrogen gas (H2) or, in some cases, water (H2O) that can be converted to hydrogen gas by electrolysis. Some green hydrogen fuel stations have solar panels and/or wind turbines, which generate electricity that is then used to power the electrolysis reaction that converts water into hydrogen and oxygen gases.
Do some internet research to answer the following questions.
1. Write a word equation and a balanced chemical equation for the electrolysis of water, also known as ‘water splitting’.
2. Why is a hydrogen fuel station regarded as ‘green hydrogen’?
1. Define ‘native metal’.
2. Name an example of a metal from this chapter that can be extracted by: a) reacting with carbon b) electrolysis.
The production of a gas is one of the indicators of a chemical change. Three common gases that can be produced in the laboratory are hydrogen, oxygen and carbon dioxide. The evidence of their production is generally bubbles (effervescence) in a solution.
Hydrogen is a product of the reaction of a metal and an acid. An example is magnesium and hydrochloric acid. The word and balanced chemical equations are shown below.
Word:
Another example is oxygen being produced from the decomposition of hydrogen peroxide. The word and balanced chemical equations are shown below.
Word:
Chemical:
hydrogen peroxide → water + oxygen
2H2O2 → 2H2O + O2
Carbon dioxide is the product of a reaction between a metal carbonate and an acid. An example is calcium carbonate and hydrochloric acid. The word and balanced chemical equations are shown below.
Word:
Chemical:
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
When one of these three gases is produced from a reaction, there are some diagnostic tests that can be used to identify the gas. When a flame is placed in hydrogen gas, a chemical reaction occurs, producing a popping sound. This is known as the pop test. If a matchstick flame is place in oxygen, it will burn even brighter, and this is called the glowing splint test. Finally, the diagnostic test for carbon dioxide is called the limewater test: when bubbles of carbon dioxide are passed through a solution of limewater (calcium hydroxide), the solution turns milky white. These tests are summarised in Table 6.3.
+ O2 → 2H2O
Practical 6.4
preparation of hydrogen, oxygen and carbon dioxide gases
Aim
To prepare hydrogen, oxygen and carbon dioxide gases and confirm their identity using diagnostic tests.
Materials
• 1 g manganese(IV) oxide
• 10 mL measuring cylinder
• 2 × Pasteur pipettes
• 5 mL hydrogen peroxide solution (30%)
• 5 × test tubes
• calcium carbonate
• hydrochloric acid (2 mol/L)
• magnesium strip
• matches
• stopper and delivery tube
• test tube rack
• wooden splint
Method
PART A – Preparation of hydrogen and the pop test
1. Place the magnesium strip in a test tube.
2. Using a Pasteur pipette, add hydrochloric acid (2 mol/L) to the test tube until the magnesium strip is completely immersed.
3. Quickly cover the test tube with another invertd test tube to collect the gas produced (see Figure 6.23).
4. Light a wooden splint with a match and place the flame below the inverted test tube. Record your observations.
PART B – Preparation of oxygen and the glowing splint test
1. Place 1 g of manganese(IV) oxide powder into a test tube.
2. Using a Pasteur pipette, add hydrochloric acid (2 mol/L) to the test tube until the calcium carbonate powder is completely immersed.
3. Light a wooden splint with a match and place the flame above the test tube. Record your observations.
PART C – Preparation of carbon dioxide and the limewater test
1. Using a Pasteur pipette, add a few millilitres of limewater to a test tube.
2. Into a new test tube place a spatula tip of calcium carbonate powder.
3. Measure 5 mL of hydrogen peroxide solution (30%) in a 10 mL measuring cylinder.
4. Add the hydrogen peroxide solution to the test tube containing the calcium carbonate powder.
5. Immediately place the stopper and delivery tube onto the test tube containing the hydrogen peroxide solution, and place the end of the delivery tube into the solution of limewater (see Figure 6.24). Record your observations.
Delivery tube
Results
Record your observations for each diagnostic test in the table below.
Table showing results of diagnostic tests for hydrogen, oxygen and carbon dioxide
Part A
Part B
Part C
Discussion
1. Write a word equation and a balanced chemical equation for the reaction occurring in Part A, and for the reaction occurring in the diagnostic test.
2. Write a word equation and a balanced chemical equation for the reaction occurring in Part B, and for the reaction occurring in the diagnostic test.
3. Write a word equation and a balanced chemical equation for the reaction occurring in Part C, and for the reaction occurring in the diagnostic test.
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For thousands of years, Aboriginal and Torres Strait Islander Peoples have used fire to sustain Australian bushland and plant growth. Conduct some research on the benefits of firestick farming or cultural burning practice and answer the following questions.
1. What is cultural burning?
2. At what time of year, in the north of Australia, is cultural burning most effective and why?
3. What are the products of combusting plant material in excess oxygen?
4. How are local Aboriginal and Torres Strait Islander Peoples’ fire management practices informing and being adopted in Western Australia’s fire management?
5. Consider why cultural burning is considered a sustainable practice.
Section 6.3 review
Online quiz
Section questions
Remembering
1. Define ‘electrolysis’.
2. List three metals that can be found in the earth as native metals.
Understanding
3. Balance the following equation: H2O2 → H2O + O2
Applying
4. Write a balanced chemical equation from the word equation: oxygen + hydrogen → water
Analysing
Teachers can assign tasks and track results
5. Write a balanced chemical equation for the reaction of calcium carbonate and hydrochloric acid to form calcium chloride, carbon dioxide and water.
Evaluating
6. Evaluate how bubbles of an unknown gas might be identified using diagnostic tests. Note: The unknown bubbles are either hydrogen, carbon dioxide or oxygen.
Chapter checklist
Success criteria
Linked questions
6.1I can identify indicators of chemical changes. 1
6.1I can identify the reactants and products in a chemical equation. 2
6.2I can recall the law of conservation of mass. 3, 5
6.2I can interpret a word equation and a balanced chemical equation for a chemical reaction. 5, 8
6.3I can recall the chemical processes of electrolysis and the reaction of metals and carbon. 7
6.3I can explain how the gases hydrogen, oxygen and carbon dioxide can be prepared. 4, 9
Scorcher competition
Review questions
Remembering
Review questions
Data questions
1. List five indicators of chemical change.
2. Describe what is happening in the following reaction. Use these keywords: reactants, product, reaction conditions.
3. State the law of conservation of mass.
Understanding
4. Write the word equation for the production of hydrogen from magnesium and hydrochloric acid.
5. Explain how a balanced chemical equation can provide evidence of the law of conservation of mass.
Applying
6. Write a word equation for the reaction of nitrogen gas and hydrogen gas to produce ammonia.
7. Compare the conditions required for the reaction of a metal with carbon with those required for an electrolysis reaction.
Go online to access the interactive chapter review
Analysing
8. Analyse the following word equation and formula equation. hydrochloric acid + zinc → zinc chloride + hydrogen
2HCℓ + Zn → ZnCℓ2 + H2
Identify:
a) the reactants
b) the products
c) whether it observes the law of conservation of mass
d) the chemical formula of magnesium chloride
Evaluation
9. Write a balanced chemical equation for the production of the following gases:
a) hydrogen
b) oxygen
c) carbon dioxide.
10. Reactants weighing a total of 20 g were reacted together. Only 18 g of product was made. Propose what may have happened to the remaining 2 g of mass.
Data questions
Various fuel sources are listed in Table 6.4, with the relative number of carbon atoms per molecule of fuel, and the mass of CO2 produced by burning 1 kilogram of each fuel. This information is also shown as a graph in Figure 6.26.
Table 6.4 The relative number of carbon atoms per fuel molecule and the mass produced by burning 1 kg of fuel
Number of carbons in fuel molecule
Figure 6.26 The relative number of carbon atoms per fuel molecule versus the mass of CO2 produced by burning 1 kg of fuel
1. Identify the fuel that produces the lowest mass of carbon dioxide per kilogram burned.
2. A premium unleaded (petrol 98) brand has stated that their fuel produces less carbon dioxide emissions than a petrol 91 brand. Determine whether this statement is correct.
3. A coal mining company has argued that the mass of carbon dioxide produced by burning 1 kg of their fuel is less than 1 kg more than that produced from natural gas. Determine whether the evidence from Table 6.4 supports this claim.
4. Identify the trend between the number of carbon atoms per reactant molecule and the mass of carbon dioxide produced.
5. Generally, at atmospheric temperature, fuel molecules with four carbons or less are gaseous fuels, and those with five or more carbons are liquid fuels. Coal is a solid fuel. Classify the fuels in Table 6.4 as gas, liquid or solid.
6. A fuel company is producing a new biofuel made primarily from ethanol, which is a molecule with two carbon atoms. Predict the mass of carbon dioxide that would be produced by burning 1 kg of this fuel.
7. For a given volume of coal and natural gas, deduce which one contains more carbon atoms.
8. Extrapolate the data to predict the mass of carbon dioxide that would be produced by burning a fuel with 11 carbon atoms per molecule.
Science has applications in all industries, including medicine, technology, business – and even the food and beverage industry.
Baristas in Australian coffee shops know the frustration of milk curdling. They want to offer rice milk, almond milk, coconut milk, lactose-free milk, soy milk and cow’s milk, but these all respond differently when heated and added to tea and coffee.
Curdling is coagulation that occurs when the protein components of milk clump together. It can occur when the acidity or temperature of the milk is changed. Soy milk is particularly susceptible to curdling.
Sometimes you might want curdling; for example, when you make yoghurt or cheese. But for a soy latte, curdling is undesirable.
Chemical engineers apply the principles of chemistry, biology, physics and maths to implement best-practice strategies involving chemicals, drugs and food. For example, an Australian milk brand, MILKLAB, worked with baristas to create a soy milk that would not curdle in acidic coffee blends.
Not all coffee shops can afford speciality products, so adding sodium bicarbonate (baking soda) to coffee to prevent soy milk curdling is a cheaper alternative. However, although baking soda is safe and effective, adding too much can affect the flavour of the coffee, so it’s best used sparingly!
Create an infographic for baristas, based on your experimentation results, for best practice with milk. Use images from your experimentation process.
As the chemical engineer representing the Hipsters Coffee Union of Australia, you are responsible for ensuring that baristas know how to make a coffee in which the milk does not curdle. You will propose the best pH, temperature and ratio of volume of coffee to milk for a range of milk types in order to prevent curdling. To do this, you will need to design several tests or trials. Be sure your milk samples are fresh, use the same amount of milk for each test, determine a way of measuring the acidity of the milk and record the weight of any curdled milk produced. Record all data, amounts and settings for your trials, so you can create your infographic for the Union with confidence.
Note: An infographic is a visual representation of information, designed to make the data and information easy to understand. Infographics are different from graphs, which are meant to be analysed. An infographic is simple, understandable, and meant to communicate messages quickly.
• white vinegar or fresh lemon juice (both have a pH of approximately 2)
• instant coffee
• a range of milks, including cow’s and soy
• water
• beakers
• measuring cylinder
• transfer bulb pipettes
• spoons or stirring rods
• clear plastic cups for cold coffee
• kettle
• paper towels
• several pieces of cheesecloth or cotton fabric
• thermometer
• data-logging pH meter or alternative method for measuring pH
• digital balance
• permanent marker
• gloves
1. Conduct some research on the process of how milk curdles and list all the factors.
2. Conduct some research and list the ingredients used in barista-made coffee, and the ratios involved. Take note of any temperatures and pH values of the ingredients. Make sure you include research on all the suggested materials.
3. Design an experiment that demonstrates the conditions under which combining coffee and milk either curdles the milk or achieves a smooth texture. Think about how milk curdles and see if you can replicate this situation.
4. Conduct your experiment, taking photos and recording your observations along the way.
5. Create an A5 ‘cheat sheet’ of infographics for baristas to easily identify the ratios of normal milk and soy milk with acidic coffee blends. Do this by hand or search for free online infographic design tools.
Do not consume any of the food. Take care when handling boiling water.
6. Discuss your findings with your colleagues and present your infographic.
7. Propose the best ratio of coffee to milk for preventing the curdling of milk for acidic coffee blends with different milk products.
8. Identify possible sources of error in your procedure and suggest ways to improve and modify your experiments.
9. Predict how the temperature of the milk may have affected your findings.
Introduction
Earth is a complex system of interconnecting spheres and the cycles that link them. Many climatic processes are the result of interactions between the spheres, which create a dynamic global climate. Changing interactions have caused Earth's climate to change in the past. It is still changing in the present and is predicted to change in the future. In this chapter, you will learn how the natural cycles of climate change are affected by humans. You will understand the factors that regulate, and the evidence for, global climate change and learn how scientists predict changes to Earth’s climate.
The spheres:
• Overlap one another
• Interact with each other
• Are affected by natural events
Earth’s chemical spheres:
• Atmosphere
• Biosphere
• Hydrosphere
• Geosphere
Nutrients are cycled throughout the spheres.
Section 7.1
Section 7.2
Section 7.3
Section 7.4
Section 7.5
• Predicting changes to climate
• Mitigating the effects and impacts of climate change
The global climate has changed over time.
Greenhouse effects can be natural or enhanced.
Enhanced greenhouse effects are caused by human activities.
Strategies to reduce greenhouse emissions:
• Renewable energy
• Carbon capture and storage
• Reforestation
• Sustainable agriculture
• Policy and regulation
Indicators of climate change:
• Ocean and atmospheric temperatures
• Sea levels
• Biodiversity
• Species distribution
• Permafrost
• Sea ice
Curriculum content
Earth and space sciences
Global systems, including the carbon and water cycles, rely on interactions involving the biosphere, lithosphere, hydrosphere and atmosphere
• the impact of human activity on the carbon cycle
• the impact of human activity on local freshwater availability
• main potable water resources for Western Australia, such as surface water, ground water and desalinated water
Changes to global systems can be used to explain patterns of global climate change
• indicators of climate change, such as changes in oceanic and atmospheric temperatures, sea levels, species distribution, permafrost and sea ice coverage
• changes in global climate over time
Collaborating and applying
Illustrate how advances in scientific understanding often rely on developments in technologies and engineering and technological and engineering advances are often linked to scientific discoveries
• considering how computer modelling has improved knowledge and predictability of phenomena, such as climate change and atmospheric pollution
© School Curriculum and Standards Authority
Glossary terms
anthropogenic
aquifer
atmosphere
biosphere
carbon sequestration
carbon sink
carbon source
climate
decomposer enhanced greenhouse effect
evaporation geosphere glacial period global warming greenhouse effect greenhouse gas groundwater hydrosphere infiltration interglacial period
lithosphere percolation precipitation sphere sustainable ecosystem trade winds transpiration weather
At the end of this section, I will be able to:
1. Distinguish between Earth’s chemical spheres: atmosphere, biosphere, geosphere and hydrosphere.
2. State that the Sun’s radiation and its interactions with Earth’s spheres are the foundation for the global climate system.
Earth can be considered a system made up of various interconnected subsystems that interact and influence one another. These subsystems, or spheres, include the atmosphere, hydrosphere, geosphere and biosphere. Each of these spheres has unique physical, chemical and biological properties, but they are not isolated from one another. They are interconnected through processes such as the carbon cycle, nutrient cycling and energy flow. These processes ensure that the Earth system operates in a delicate balance, with changes in one sphere having consequences for the others. spheres
The atmosphere is a layer of gases that surrounds Earth. It is composed of various gases, including nitrogen (78%), oxygen (21%), argon (1%) and trace amounts of other gases such as carbon dioxide and neon. The atmosphere regulates Earth’s temperature and protects it from harmful radiation, and it plays a critical role in the water cycle. It is made up of several layers, including the troposphere, stratosphere, mesosphere, thermosphere and exosphere (see Figure 7.2), each with distinct characteristics and properties.
Quick check 7.1
1. Name the gas that is the most abundant in Earth’s atmosphere.
2. Recall the functions of Earth’s atmosphere.
The troposphere is the lowest layer of Earth’s atmosphere, extending from Earth’s surface to an altitude of approximately 6 to 20 kilometres. It is where most weather occurs and is where most of the water cycle occurs. Water evaporates from Earth’s surface into the atmosphere, forming clouds through condensation, and eventually precipitates as rain, snow or other forms of precipitation. The troposphere is composed mainly of nitrogen and oxygen, along with trace amounts of other gases, such as water vapour, carbon dioxide and methane.
The temperature in the troposphere decreases with increasing altitude, which is why the highest temperatures are near Earth’s surface and the lowest temperatures are at the top of the layer. This temperature gradient leads to convection currents, which drive weather patterns and atmospheric circulation. The troposphere is critical for supporting life on Earth, because it provides the oxygen we breathe, regulates Earth’s temperature and plays a vital role in the carbon and water cycles.
The stratosphere is the layer of Earth’s atmosphere above the troposphere, extending from approximately 20 to 50 kilometres in altitude. It is characterised by a relatively high concentration of ozone, which absorbs harmful ultraviolet radiation from the Sun. The temperature in the stratosphere increases with altitude because the ozone layer absorbs solar radiation, which creates a stable layer that inhibits mixing with the troposphere below. The boundary between the troposphere and the stratosphere is home to the jet stream, a highaltitude, fast-moving wind that influences weather patterns. The stratosphere plays a crucial role in regulating Earth’s temperature.
1. List some features of the troposphere.
2. State the function of the ozone layer in the stratosphere.
In 1985, scientists found that parts of the ozone layer above the continent of Antarctica had broken down. They also noticed that similar thinning of the ozone layer was happening over parts of Australia, and that this correlated with an increase in cases of skin cancer. They needed to find out why this had happened and if it could be reversed. Do some research and answer the following.
1. Compare the atomic structures of oxygen gas (O2) and ozone gas (O3).
2. Identify the main function of the ozone layer in more detail, to explain the impact of ozone thinning.
3. Research the causes of ozone thinning.
4. Describe the purpose of the Montreal Protocol.
above Antarctica. The bluish-purple areas show the least amount of ozone.
5. In October 2022, a UN-backed scientific panel released a report saying the ozone layer is on track for a full recovery. When did they predict this would happen by?
The biosphere is the thin layer of Earth where life can exist. It is made up of all the living organisms on the planet, including plants, animals and microorganisms, as well as the physical environments in which they live.
The biosphere extends from the deepest parts of the ocean to the lower atmosphere, and from the polar ice caps to the Equator. It is a complex and interconnected system, with organisms relying on each other for survival and functioning together to maintain the delicate balance of the planet’s ecosystems.
Quick check 7.3
7.6 Human activities, such as pollution and deforestation, can have significant impacts on the biosphere and disrupt the balance, leading to negative consequences for living organisms.
1. Recall the definition of the biosphere.
2. 'Flying birds are part of the atmosphere.' Is this statement true or false? Justify your choice.
The hydrosphere is all the water on Earth, including oceans, rivers, lakes, groundwater and even water in the atmosphere. It plays a critical role in supporting life on Earth, because all living organisms require water to survive. The hydrosphere also plays a key role in regulating Earth’s climate, because it absorbs and distributes heat throughout the planet. Additionally, the movement of water in the hydrosphere, such as through the water cycle, helps to shape Earth’s surface and create important habitats for various organisms.
7.7 The hydrosphere faces numerous threats, such as pollution, overuse and climate change.
biosphere all the areas on Earth and in its atmosphere that contain life hydrosphere all the water on Earth (e.g. lakes and rivers)
Quick check 7.4
1. Recall the definition of the hydrosphere.
2. State an example of something that is part of the hydrosphere.
geosphere
Earth’s magma, lava, rocks and minerals
lithosphere the geological parts of Earth’s crust and upper mantle only
The geosphere is the solid and fluid rock and mineral parts of Earth, including the crust, mantle and core. It is the largest of Earth’s four major spheres, and it plays a crucial role in supporting life on the planet. The geosphere provides the foundation for Earth’s surface features, including mountains, valleys and plateaus. It is also home to valuable natural resources, such as minerals and fossil fuels, which are essential to human societies.
Figure 7.8 The geosphere is constantly undergoing changes due to natural processes such as plate tectonics, erosion and volcanic activity, which can lead to earthquakes, landslides and other hazards.
The lithosphere is often included in discussions of Earth’s global spheres. It is the outermost layer of Earth’s crust and the uppermost section of the mantle. In contrast, the geosphere encompasses all the minerals and rocks on Earth, extending from the crust to the inner core. The lithosphere is divided into numerous tectonic plates that rest on the underlying mantle. Many seismic and volcanic events occur along the boundaries between these plates.
Quick check 7.5
1. Recall the definition of the geosphere.
2. State an example of something that is part of the geosphere.
Earth's spheres are interconnected, forming a complex system that drives nutrient cycling, cycles and energy flow. These connections allow vital elements such as carbon, nitrogen and phosphorus to circulate between spheres, supporting ecosystems and maintaining Earth’s balance.
Nutrient cycling depends on the interaction of spheres. The atmosphere contains nutrients in gaseous form, such as carbon dioxide and nitrogen gas, which are absorbed by the biosphere through photosynthesis and nitrogen fixation. In the biosphere, plants, animals and microorganisms use these nutrients for growth and energy, returning them to the environment through respiration, decomposition and egestion. The hydrosphere transports dissolved nutrients, such as nitrates and phosphates in water, facilitating their uptake by aquatic organisms and deposition in sediments. The lithosphere stores nutrients in soils and rocks, releasing them through weathering processes and absorbing them into sediments through geological activity. These continuous exchanges ensure that nutrients are distributed and recycled, sustaining ecosystems.
Energy flow also illustrates the connections between spheres. Solar energy drives photosynthesis in the biosphere, providing the energy foundation for ecosystems. Energy is then transferred through food webs in the biosphere and dissipates as heat into the atmosphere. Geothermal energy from the lithosphere also contributes to processes such as volcanic activity, influencing atmospheric and hydrospheric conditions.
The Sun’s radiation forms the foundation of Earth’s climate system. Radiation that reaches Earth’s surface interacts with the different spheres and drives various atmospheric, oceanic and land processes that collectively determine the global climate. The Sun’s radiation heats air and water, evaporates water into the air, and drives wind and ocean currents. These interactions create weather patterns and climate zones, which can be seen in Figure 7.9. The absorption and reflection of the Sun’s radiation by Earth’s atmosphere and surface also regulate Earth’s temperature, influencing global climate.
Go online to access the interactive section review and more!
Section 7.1 review
Online quiz
Section 7.1 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Recall the correct definition for each chemical sphere.
a) Atmosphere
b) Biosphere
c) Lithosphere
d) Hydrosphere
2. Identify the correct sphere for the following examples.
a) Glacier
b) Tectonic plates
c) Earthworms
d) Ozone
3. Recall the layer of the atmosphere where most of the weather occurs.
4. Recall the second most abundant gas in Earth’s atmosphere.
5. Identify which of Earth’s spheres would contain matter that has arrived from space.
Understanding
6. Explain the problems associated with a hole in the ozone layer.
7. Describe the role of Earth’s atmosphere in sustaining life on Earth.
Applying
8. Identify examples of the chemical spheres in Figure 7.10.
9. Identify the sphere interactions taking place in Figure 7.11.
Analysing
10. Compare the geosphere with the lithosphere.
11. Analyse why a healthy river containing dissolved nitrogen, oxygen and carbon dioxide, algae and other organisms, and mineral and rock fragments, contains components from all the chemical spheres.
Evaluating
12. Decide which spheres clouds belong to, and justify your answer.
13. Discuss how a natural disaster, such as an earthquake, can affect the chemical spheres. Try to include all four spheres in your answer.
At the end of this section, I will be able to:
1. Describe the carbon cycle.
2. Describe the water cycle.
3. Describe the role of cultural burning in facilitating energy and nutrient transfers.
4. Identify the impact of human activity on local freshwater availability.
The cycling and recycling of nutrients such as nitrogen, carbon and water in the spheres is important for sustaining life and ecosystems. A sustainable ecosystem is a biological environment that can support itself without outside assistance.
The carbon cycle is the movement of carbon through all four spheres. Carbon is a key component of organic molecules such as carbohydrates, lipids, proteins and DNA that make up living organisms. Carbon is essential for the formation of the backbone of these molecules, and it is involved in energy transfer and storage within cells.
The carbon cycle occurs in many stages, but it is important to note that carbon can stay at one stage for thousands of years before moving on to the next stage.
Table 7.1 summarises the forms of carbon in each of the spheres.
AtmosphereCarbon dioxide (CO2), methane (CH4)
BiosphereCarbohydrates (e.g. glucose, C6H12O6), fats, proteins, vitamins and DNA of all living things
HydrosphereCO2 dissolved in rivers, lakes and the ocean, forming carbonic acid (H2CO3)
GeosphereDecomposed organic matter in soils
Fossil fuels (coal, oil and gas)
Limestone (calcium carbonate, CaCO3)
The carbon cycle can be summarised in seven processes (see Figure 7.12), which either increase or decrease carbon dioxide in the atmosphere:
1. photosynthesis
2. transfer of carbon through the food chain
3. respiration
4. excretion, egestion, death and decomposition
5. formation of fossil fuels
6. combustion
7. formation of limestone.
Atmospheric
Photosynthesis (1)
Respiration (3)
(2)
Decomposition (4)
Excretion and egestion (4)
Decomposition without respiration (4)
Combustion (6)
Fossil fuels (5) Factory
Dissolving
7.12 The main stages and processes in the carbon cycle
Ocean (carbonic acid) (7)
Deposits of calcium carbonate (7)
Carbon dioxide in Earth’s atmosphere is absorbed by plants during photosynthesis. The carbon dioxide reacts with water taken in from the soil to make glucose, a carbon-containing compound.
The following equations summarise the process of photosynthesis in plants.
carbon dioxide + water → glucose + oxygen
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O (full)
6CO2 + 6H2O → C6H12O6 + 6O2 (net)
The plant draws up water and minerals from the ground
Chloroplasts use light energy to make glucose.
7.13 Plants remove carbon dioxide from the atmosphere during photosynthesis.
Quick check 7.7
1. Describe a sustainable ecosystem.
2. Explain why the recycling of carbon is important.
3. State the name of the form of carbon that is in the hydrosphere.
4. Recall the form of carbon that carbon dioxide is converted into, in photosynthesis.
Animals obtain their carbon by eating plants and other animals. When animals and plants are eaten, their carbon content is transferred through the food chain.
Plants and animals break down glucose, using oxygen to form carbon dioxide and water. This process is called respiration. The carbon dioxide is added to the atmosphere when organisms breathe out.
The following equation summarises respiration.
glucose + oxygen → carbon + water + ATP dioxide (energ y)
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
Excretion, egestion, death and decomposition
Some of the carbon content of animals and plants enters the soil as waste, such as urine (excretion) and faeces (egestion).
Dead animals and plants (organic matter) also contribute to the carbon content of the soil. Waste material and dead organic matter is broken down by decomposers, which respire, releasing carbon dioxide back into the atmosphere.
Try this 7.1
Modelling decomposition
Search online for an Interactive Model of Leaf Decomposition. This will allow you to compare how different mathematical models show how climates, litter types and ecosystems affect decomposition rate.
1. Recall how animals obtain their carbon in the
2. Apart from carbon dioxide, state the other product that is released during the breakdown of glucose in respiration.
3. Name ways that animals can increase the carbon content of soil.
Fossil fuels, such as coal, oil and gas, are composed of the carbon from plants and animals that died millions of years ago. Carbon is stored as fossil fuels for millions of years before re-entering the carbon cycle.
Combustion reactions that involve the burning of fuels (such as the bushfire shown in Figure 7.18) have a significant impact on the carbon cycle because they release carbon dioxide into the atmosphere, contributing to the increase in atmospheric carbon dioxide concentrations. Often, these are fossil fuels such as coal, oil and natural gas. The following equation shows the combustion of octane, a component of oil.
and compressed for millions of years. Sometimes, fossilised plants can be found in coal.
octane + oxygen → carbon dioxide + water
2C8H18 + 25O2 → 16CO2 + 18H2O
The release of carbon dioxide from combustion reactions disrupts the natural balance of the carbon cycle. Normally, carbon moves between the atmosphere, ocean and land through processes such as photosynthesis, respiration and decomposition. However, burning fossil fuels releases carbon that has been stored underground for millions of years, disrupting the natural flow of carbon, and leading to an excess of carbon in the atmosphere.
Fire has been used as a vital land management tool by Aboriginal and Torres Strait Islander Peoples for tens of thousands of years. Cultural burning is a deeply embedded practice of caring for Country, ensuring the health of landscapes, ecosystems and communities.
Through careful and controlled use of fire, a mosaic of vegetation is maintained, supporting biodiversity and strengthening ecosystems. These fires are deliberately timed and placed, guided by deep knowledge of Country, seasonal changes and ecological relationships. Cultural burning enhances soil health, cycling nutrients back into the land and supporting the growth of plants that sustain animals and people. It also helps manage invasive species and reduce the intensity of destructive wildfires. In some cases, burning has been used as a hunting strategy, driving animals towards particular areas.
The publication of data and findings related to the reintroduction of Aboriginal and Torres Strait Islander traditional fire regimes has informed more effective fire-reduction strategies and policies in several ways. The Western Australia Parks and Wildlife Service enhances its fire management strategies by working in partnership with Aboriginal and Torres Strait Islander people.
Conduct some research on the following partnerships and how they have produced more effective fire management practices:
• the development of Kimberley Land Council's (KLC) Indigenous fire management program in the Kimberley region
• the Indigenous Desert Alliance's (IDA) Right-Way Desert Fire Project.
traditional fire management Research carried out at the University of the Sunshine Coast has found that traditional fire burning practices of Aboriginal and Torres Strait Islander Peoples can help protect koalas. The research was conducted over two years in collaboration with the Quandamooka people on North Stradbroke Island.
The study found that cultural burns are cooler, lower and slower than ‘hot fires’. The study also found that cultural burns can protect koalas by encouraging regeneration of native plants and controlling species such as banksias and wattle, reducing the risk of fire reaching the koalas’ canopy. The researchers used drones fitted with thermal cameras and hormone metabolite analysis to monitor koala stress during the cultural burns. The study found no negative impacts on koala population densities or their stress levels.
In small groups, investigate how Aboriginal and Torres Strait Islander Peoples’ fire management practices are informing and being adopted in contemporary fire management. You may want to consider how controlled burning can stimulate the growth of fire-tolerant trees and plants that can store carbon in their biomass and in the soil, or how it reduces the fuel load of an ecosystem.
Carbon dioxide gas in the atmosphere can dissolve in the oceans, forming carbonic acid. Carbon dioxide also provides the carbon that combines with calcium ion mineral deposits to make calcium carbonate (CaCO3), which is the major component of shells. Shells from dead animals sink to the bottom of the ocean. Over millions of years, these shells are compacted and form limestone.
Limestone is a sedimentary rock and an important building material in the construction industry. The carbon stored in limestone can remain there for millions of years but under certain conditions, such as weathering and erosion, carbon dioxide can be released from limestone back into the atmosphere. For example, when limestone is exposed to acidic water or soil, it can react with the acid to release carbon dioxide.
Table 7.2 summarises the gains and losses of atmospheric carbon in the carbon cycle.
Atmospheric carbon gains
Respiration
Combustion
Excretion, death and decomposition
Atmospheric carbon losses
Photosynthesis
Formation of fossil fuels
Dissolving in the oceans and forming limestone
Practical 7.1
the oceans and carbon dioxide
Aim
To determine what happens when carbon dioxide dissolves in water.
Materials
• bottle of universal indicator and pH scale
• water
• test tube
• test-tube rack
• drinking straw
Method
1. Draw the table shown in the Results section.
2. Fill the test tube with water to a depth of about 5 cm.
Be careful
Wear appropriate personal protective equipment.
Wear safety glasses. Use the correct method for blowing into the test tube.
3. Add 3 drops of universal indicator and note the colour and pH in the results table.
4. Place the straw into the test tube and blow gently into it for 10 seconds. Be careful to only blow into the straw; you might want to practise first.
5. Note the colour and pH of the solution after you have blown into it.
continued …
Results
Copy and complete the following table.
Colour and pH of water before and after blowing
Colour
Before blowing After blowing
Discussion
1. Identify what is indicated by the colour and pH of the water before blowing.
2. Identify what is indicated by the colour and pH of the water after blowing.
3. Give the name and formula of the solution formed after blowing.
4. Which stage of the carbon cycle does this experiment represent? Justify your choice.
5. Discuss what happens to carbon dioxide in water after it has dissolved.
6. Determine the ability of carbon dioxide to dissolve in water, based on this experiment.
7. Discuss the global issues behind carbon dioxide dissolving in water.
Conclusion
1. Explain how your observations support your claim.
limestone and carbon dioxide
Aim
To determine whether limestone is a store of carbon dioxide
Materials
• calcium carbonate chips
• hydrochloric acid (1 mol/L)
• limewater
• 2 × 10 mL measuring cylinders
Method
Be careful Wear appropriate personal protective equipment. Wear safety glasses.
• 2 test tubes
• test-tube rack
• delivery tube
1. Using a 10 mL measuring cylinder, measure 5 mL of hydrochloric acid and pour it into one of the test tubes.
2. Using another 10 mL measuring cylinder, measure 5 mL of limewater and pour it into the other test tube.
3. Add three calcium carbonate chips to the acid, and at the same time attach the bung of the delivery tube to this test tube with the other end in the limewater solution.
4. Observe what happens to the limewater.
Results
Record your observations from the experiment in your science journal.
Discussion
1. Describe what happened to the limewater solution.
2. In this reaction, calcium carbonate reacted with hydrochloric acid. Three products were formed. Two of those products were calcium chloride and water. Write a word equation for the reaction that includes the third product.
3. Identify the part of the carbon cycle represented by this practical.
aquifer
a body of porous rock or sediment
saturated with groundwater
check 7.9
1. State an example of a fossil fuel.
2. Name the process in which fossil fuels are burned, releasing carbon dioxide back into the atmosphere.
3. State the scientific name and formula for limestone.
The water cycle is the continuous movement of water through four major spheres of Earth: the biosphere, lithosphere, hydrosphere and atmosphere. Water is vital for all living organisms because it plays a key role in cellular processes, temperature regulation and nutrient transport. This movement of water between Earth’s spheres occurs through several key processes that cause water to be continuously recycled and distributed throughout different parts of the planet. The different forms of water in each of Earth’s spheres are summarised in Table 7.3.
AtmosphereWater vapour, clouds (condensed water droplets)
BiosphereWater in cells, tissues and organisms
HydrosphereOceans, rivers, lakes, glaciers, groundwater
GeosphereWater stored in soil, rock pores, aquifers
Table 7.3 Water in Earth's spheres
The water cycle consists of six key processes that describe how water moves through the environment.
Evaporation occurs when heat from the Sun causes water in oceans, lakes and rivers to change from liquid to vapour, which rises into the atmosphere.
Plants contribute to this process through transpiration, where they absorb water through their roots and release it as vapour from small openings in their leaves, called stomata. Together, evaporation and transpiration help regulate Earth’s climate and maintain humidity in the atmosphere.
evaporation the process by which water changes from a liquid to a gas transpiration the release of water vapour from plants into the atmosphere
As water vapour rises, it cools and condenses into tiny droplets, forming clouds. When these droplets combine and grow larger, they eventually become too heavy to remain suspended in the air. At this point, they fall back to Earth as precipitation, which can take different forms depending on temperature:
• rain – liquid water droplets
• snow – frozen ice crystals
• sleet – a mix of rain and ice
• hail – large balls of ice.
Precipitation returns water to the land and the oceans.
infiltration the movement of water from the surface into the soil
percolation the downward movement of water through the soil and rock layers, often reaching groundwater groundwater water that exists beneath the Earth's surface in soil pore spaces and rock formations, typically stored in aquifers
When precipitation reaches the ground, some of it soaks into the soil, in a process called infiltration This water then moves deeper through porous rock layers, in a process called percolation. These processes help replenish groundwater supplies, which are stored in underground reservoirs known as aquifers. Groundwater is an important source of fresh water for plants, animals and humans.
Not all precipitation infiltrates the soil. Some of it flows across the land as surface runoff, moving into rivers, lakes and eventually into the ocean. This process maintains river systems and returns water to the hydrosphere.
Groundwater also moves slowly through underground rock layers, feeding into springs, rivers and lakes over time. This process, known as groundwater flow, is particularly important in dry regions where surface water is scarce.
rebalancing our groundwater
Groundwater is water found beneath the Earth's surface. It fills the spaces between soil, sand and rocks, and provides water for drinking, agriculture and natural ecosystems. In Perth and Mandurah, about 70 per cent of water comes from groundwater sources. It helps keep wetlands healthy, supports trees in urban areas, and supplies water for industries and gardens.
Perth and Mandurah's climate has changed. Since the 1970s, rainfall has dropped by 15 per cent, leading to an 80 per cent reduction in streamflow into dams. Less rain means less water soaking into the ground, causing groundwater levels to drop. In some areas, the water table has fallen by up to 10 metres!
This has led to:
• drying wetlands, such as Wagardu (Loch McNess) in Yanchep National Park
• loss of ecosystems, including caves that rely on groundwater
• acidic lakes, affecting plants and animals
• saltwater intrusion, making bore water salty near the coast.
To help rebalance groundwater levels, the Western Australian government has:
• built desalination plants to provide drinking water without relying on rainfall
• created a groundwater replenishment scheme, which cleans waste water and puts it back into aquifers
• introduced water restrictions, including limits on garden bore use, to save up to 30 billion litres of water per year.
Find out where your local water supply comes from. Is groundwater an important source of water in your area? Think of one way your community could save groundwater. How would it work? Write a short explanation or draw a diagram. Do you think water restrictions are enough to protect groundwater, or should stronger action be taken?
1. Recall why water is essential for living organisms.
2. State the key processes that move water through the water cycle.
3. State the difference between evaporation and transpiration.
Human activities can significantly disrupt the natural water cycle. Below are listed some of the major impacts.
• Deforestation – cutting down trees reduces transpiration, leading to lower humidity and decreased rainfall. It also increases surface runoff, which can cause soil erosion and reduce groundwater recharge.
• Agriculture – farming requires large amounts of water for irrigation, which can deplete groundwater supplies. Additionally, fertilisers and pesticides can contaminate freshwater sources, harming ecosystems.
• Urban development – cities and roads prevent water from infiltrating the soil, increasing runoff and reducing groundwater recharge. Stormwater systems can quickly carry polluted water into rivers and oceans.
• Overuse of groundwater – extracting too much groundwater lowers water tables, making it harder for wells to access fresh water. In coastal areas, saltwater intrusion can occur, where the seawater moves into freshwater supplies, making them undrinkable.
• Climate change – rising global temperatures increase evaporation rates, change rainfall patterns and lead to more extreme weather events, such as droughts and floods, which affect water availability.
1. Describe how deforestation affects the water cycle.
2. Explain why agriculture affects the availability of fresh water.
3. Recall how urban development increases surface runoff.
Potable water is water that is safe and suitable for human consumption, and free from harmful contaminants and pathogens. It is essential for drinking, cooking and sanitation, supporting public health and wellbeing. Access to clean, potable water is crucial for preventing waterborne diseases and maintaining hygiene.
The availability of potable water is influenced by factors such as natural water sources, treatment processes and effective water management. Ensuring a sustainable supply of potable water is an ongoing challenge for many regions, as the global population grows and water resources become scarcer. In Western Australia, potable water is sourced primarily from three main supplies: surface water, groundwater and desalinated water.
• Surface water is collected from rivers, reservoirs and dams, but its availability changes depending on rainfall patterns. During dry seasons, less water is available, increasing reliance on other sources.
• Groundwater is extracted from underground aquifers, and is an essential resource. Excessive use without natural replenishment can lead to depletion. In coastal areas, overuse of groundwater can cause saltwater intrusion, making it undrinkable.
• Desalinated water is produced by removing salt from seawater, providing a reliable alternative source of drinking water. However, the process requires a lot of energy and is expensive to maintain.
Several beverage companies have been extracting groundwater for bottled drinks from bores in Western Australia for decades, often without needing a licence.
Experts argue that current laws, based on outdated common law principles, allow landholders to take groundwater without regulation. With Perth experiencing an increase in drought conditions and groundwater recharge dropping by up to 70% over 50 years, there is growing debate about how water resources should be managed and whether industries should be held to stricter ethical and environmental standards.
In your class, discuss the ethical issues around water extraction for bottled drinks. Identify the different groups affected by this issue, such as companies, local farmers, the government and consumers. Think about the motivations and concerns of each group – who benefits and who faces risks? Who has the right to access water? Should water be protected as a public resource? Suggest possible solutions that could balance economic needs, environmental sustainability and fairness to the community. Consider how your solutions might help solve this issue fairly for everyone involved.
Quick check 7.12
1. Recall the three main sources of drinking water in Western Australia.
2. Explain why surface water availability changes over time.
3. Describe a major drawback of desalination.
Section 7.2 review
Online quiz
Section 7.2 questions
Remembering
Section questions
Teachers can assign tasks and track results
Go online to access the interactive section review and more!
1. State the name and formula of a compound in which carbon is found in the atmosphere.
2. Recall why animals and plants require carbon.
3. State the name of the process in which water changes from a liquid to a gas.
4. Select the best definition for a sustainable ecosystem and justify your choice.
A. An environment that requires intervention to continue
B. A biological environment that is self-sustaining; that is, it does not require any outside assistance
C. A system that is a mixture of biotic and abiotic factors
Understanding
5. Explain, with the use of a word equation, why respiration is part of the carbon cycle.
6. Describe the process of photosynthesis to show how carbon dioxide from the atmosphere is transferred to plants and animals.
7. Explain the difference between infiltration and percolation.
8. Summarise the role of decomposers in the carbon cycle.
9. Explain where the carbon in coal, oil and gas originally came from.
10. Describe how carbon moves between the atmosphere and the biosphere.
Applying
11. Explain how the water cycle would change if a region experienced a dramatic increase in urbanisation. Consider factors like evaporation, precipitation and infiltration.
12. Apply your understanding of the carbon cycle to explain how changes in land use, such as converting forests into farmland, can affect atmospheric carbon levels.
Analysing
13. Infer what would happen to the carbon cycle if all human activities that emit carbon were suddenly stopped.
14. Infer what would happen to the water cycle if there were no plants to carry out transpiration.
15. Categorise the following as atmospheric carbon gains or atmospheric carbon losses.
a) Formation of fossil fuels
b) Respiration
c) Excretion
d) Photosynthesis
e) Limestone formation
f) Combustion
Evaluating
16. Evan says that humans are affecting the carbon cycle in a negative way. Trent disagrees with this statement and thinks that humans have no effect at all. Decide who you think is correct.
17. Discuss the role of limestone in the carbon cycle.
18. Discuss how burning fossil fuels and deforestation affect the carbon cycle.
At the end of this section, I will be able to:
greenhouse gas a gas that contributes to the greenhouse effect
1. Describe the greenhouse effect and relate it to the role carbon dioxide plays in maintaining temperatures that support life on Earth.
2. Describe the impact of human activity on the carbon cycle.
3. Describe strategies that can reduce carbon dioxide emissions.
4. Identify how carbon dioxide is captured and stored naturally or through the use of technologies.
In extremely cold regions, it is not possible to grow some fruits and vegetables. In these places, growers may use greenhouses to cultivate weather-sensitive or temperature-sensitive plants or plants that are out of season. Greenhouses provide a protective shield against harsh weather conditions, ensuring optimal growth conditions for the plants. The advantage of using a greenhouse is that it offers more control over the growth conditions, allowing growers to tailor the environment to the specific needs of the plants.
Greenhouses are typically constructed from glass. When the Sun’s radiation passes through the greenhouse’s walls and roof, it heats the ground and air inside the greenhouse. The heated ground emits infrared radiation, which is reflected back into the greenhouse by the glass. The hot air rises but cannot leave the greenhouse (see Figure 7.26). As a result, the temperature inside rises. This helps to keep the plants at an optimum temperature, promoting growth.
Greenhouses protect plants from cold and adverse weather conditions by keeping in the thermal energy.
1. Name a type of radiation emitted from the hot ground.
2. Explain why greenhouses are made of glass.
Earth naturally retains heat through a process similar to a greenhouse, but on a much larger scale. Most of the Sun’s radiation enters Earth’s atmosphere and warms the ground and oceans. Some of the radiation is reflected back into space by ice, clouds and water. However, the ground and oceans continue to emit radiant energy back towards the atmosphere in the form of infrared radiation. This infrared radiation is absorbed and reflected back towards the surface by a layer of gases known as greenhouse gases. Water vapour (H2O) is the most abundant greenhouse gas, making up 95% of the total. Methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) are three of the other most common greenhouse gases.
Table 7.4 compares the effectiveness in retaining heat of the three most common greenhouse gases after water vapour. Methane is more effective than carbon dioxide at trapping heat, and therefore it has a higher global warming potential, meaning it can absorb more heat per unit of mass than CO2. However, CO2 is much more abundant in the atmosphere and has a longer lifespan, so overall it has a greater impact on global climate.
atmosphere.
Proportion of total greenhouse gases (%) 84 9 5
Persistence in the atmosphere 100 years 10 years 100 years
Effectiveness of trapping heat compared to carbon dioxide 30 times more effective 300 times more effective
Table 7.4 A summary of the three most common greenhouse gases, excluding water vapour
The process by which the Sun’s solar energy is trapped in Earth’s atmosphere is known as the greenhouse effect. The Sun’s radiation, primarily in the visible light wavelength, can pass directly through the atmosphere because it has a short wavelength. However, long-wave radiation emitted from the ground and oceans in the form of infrared radiation is absorbed by greenhouse gases, which then re-emit the radiation in all directions, including back towards the Earth’s surface, raising atmospheric temperatures and keeping the Earth warm. This process is crucial for the survival of organisms, as it helps regulate Earth’s climate and ensures conditions that support life. If greenhouse gases were absent, infrared radiation from the Earth’s surface would escape more freely, disrupting this temperature regulation.
Infrared radiation is radiated into space.
Infrared radiation is absorbed and reflected by greenhouse gases.
Ground and oceans emit infrared radiation. Greenhouse gases Radiation heats up the ground and oceans.
greenhouse effect the trapping of the Sun’s warmth by a layer of gases in the lower atmosphere
enhanced greenhouse effect the intensifying of the natural greenhouse effect due to human activity
global warming the long-term rise in the average temperature on Earth, primarily caused by the increase of greenhouse gases in the atmosphere
Table 7.5 summarises the features of UV-visible light and infrared radiation.
Source Sun Sun, ground and oceans
WavelengthShort Long
Trapped or notNot trapped by atmosphereTrapped by greenhouse gases in atmosphere
1. State the name and formula of one common greenhouse gas.
2. Most of the radiation emitted from the Sun heats the ground and the oceans. Describe what happens to the rest of this radiation.
3. Name a source of short-wave radiation.
4. Name the radiation that is absorbed by greenhouse gases in the atmosphere.
Greenhouse gases can absorb a certain amount of infrared radiation; the rest is radiated back into space. The more greenhouse gases there are in the atmosphere, the more infrared radiation is trapped and the hotter Earth becomes.
The enhanced greenhouse effect is a phenomenon in which human activities, such as burning fossil fuels and deforestation, release large amounts of greenhouse gases, such as carbon dioxide, into the atmosphere. These gases trap more heat from the Sun, which increases the temperature of Earth’s atmosphere and surface, leading to global warming. This is disrupting the carbon cycle by increasing atmospheric carbon dioxide levels beyond what can be absorbed by natural processes.
The major cause of the enhanced greenhouse effect is increased concentrations of greenhouse gases (carbon dioxide, methane, nitrous oxide and water vapour) in the atmosphere. Table 7.6 summarises how humans have contributed to the increased levels of these greenhouse gases.
Greenhouse gas
How humans have increased its concentration in the atmosphere
Carbon dioxideBurning fossils fuels such as coal, oil and gas. In 2023, fossil fuels contributed 65% of total electricity generation, including coal (46%), gas (17%) and oil (2%).
Methane Farming cattle (which produce methane when they digest grass) and growing rice in paddies. Increased temperatures lead to the melting of permafrost. Permafrost is frozen soil that contains trapped methane produced from the decomposition of plants and animals.
Nitrous oxideUsing fertilisers increases the amount of nitrogen in the nitrogen cycle, therefore increasing the production of nitrous oxide.
Water vapourAlthough water vapour is naturally the most abundant greenhouse gas, as the concentrations of carbon dioxide, methane and nitrous oxide increase due to human activity, more heat is trapped, which contributes to increasing water vapour concentrations (increased humidity). This has a positive feedback effect on increasing temperatures, enhancing the greenhouse effect.
Table 7.6 How humans have increased the concentration of greenhouse gases in the atmosphere
Try this 7.2
Reinstatement of traditional fire management practices
Conduct some research on how technological advances in monitoring greenhouse gas emissions and other environmental factors have contributed to the reinstatement of traditional fire management practices as a strategy to reduce atmospheric pollution.
1. State one way in which we have increased the concentration of carbon dioxide in the atmosphere.
2. State one way in which we have increased the concentration of nitrous oxide in the atmosphere.
3. Describe what the enhanced greenhouse effect has led to.
Comparing the natural and enhanced greenhouse effects
Aim
To compare the impacts of the natural and enhanced greenhouse effects
Materials
• baking soda
• water
• vinegar
• 2 × 500 mL beakers
• 100 mL measuring cylinder
• cling wrap
Method
Part 1: Prepare the results table
• 2 elastic bands
• 2 weighing boats
• balance
• marker pen
• sticky tape
• stopwatch
Be careful
Take care when handling the lamp because it can become hot with prolonged use. Wear heat-resistant gloves.
• 2 thermometers
• high-intensity lamp
• heat-resistant gloves
1. Read the rest of the steps in the method and make a prediction about what will happen.
2. Create an appropriate results table for this experiment.
Part 2: Prepare the equipment
1. With the marker pen, label one of the 500 mL beakers ‘Control’.
2. Using the sticky tape, tape one of the thermometers to the inside of this beaker. It must be about 5 cm above the bottom of the beaker.
3. With the marker pen, label the second beaker ‘CO2’.
4. Tape the thermometer to the inside of this beaker, again making sure it is 5 cm from the bottom.
5. Prepare the cling wrap and elastic bands for sealing; you will cover each beaker immediately after you have poured in the liquid.
Part 3: Collect the data
1. Using the balance, weigh 35 g of baking soda into each weighing boat and pour it into each beaker.
2. Using the 100 mL measuring cylinder, measure 65 mL of water and pour it into the control beaker. Immediately cover it with the cling wrap and elastic band.
3. Using the same 100 mL measuring cylinder, measure 65 mL of vinegar and pour into the CO2 beaker. Immediately cover it with the cling wrap and elastic band.
4. Swirl the contents of each beaker to make sure that the baking soda has fully dissolved.
5. Place both beakers underneath the lamp.
6. Record the starting temperature of each atmosphere before the lamp is turned on.
7. Turn on the lamp and start the stopwatch.
8. Measure the temperature in each beaker every 2 minutes for 8 minutes. Record the temperatures in your results table.
9. At 8 minutes, measure the temperature and then turn off the light.
10. Record the final temperature 2 minutes later.
Results
1. Calculate the increase in temperature in each container by calculating the difference between the temperature at 8 minutes and the starting temperature.
2. Calculate the thermal energy retention by calculating the difference between the temperature at 8 minutes and the temperature at 10 minutes.
Discussion
1. State which container showed the greatest increase in temperature. Does it match your prediction?
2. State which container retained the most thermal energy in the final 2 minutes.
3. Explain these results by using your own knowledge and scientific research.
Conclusion
1. State a conclusion about the enhanced greenhouse effect based on this experiment.
2. Support the statement by using your data.
A carbon footprint is the volume of greenhouse gases (including carbon dioxide) emitted into the atmosphere as a result of the actions of a specific individual, event, organisation or product.
methods of transport have a bigger environmental impact than others.
• Search online for a reliable carbon footprint calculator. Suggested websites include the United States Environmental Protection Agency or the Global Footprint Network.
• Gather information on your daily habits such as transportation, energy usage, diet and waste management.
• Use the carbon footprint calculator to input your daily habits and activities. The calculator will provide you with an estimate of your carbon footprint in metric tonnes.
• Analyse your carbon footprint results and identify areas where you can reduce your carbon emissions. For example, consider walking or riding a bicycle instead of travelling to school by car, reducing energy consumption at home, or reducing waste.
Try this 7.3
Reducing carbon footprints Plan
Carbon dioxide emissions from human activity are our most significant contributor to the enhanced greenhouse effect. Since the Industrial Revolution in the 1800s, we have been burning large amounts of fossil fuels for energy. This means we have been moving stored carbon from the lithosphere into the atmosphere, directly affecting the balance of the carbon cycle.
As part of the carbon cycle, Earth has carbon sources, which are processes or areas that release carbon (such as the atmosphere), and carbon sinks, which are areas where carbon is stored (such as the oceans, forests or fossil fuels).
Burning fossil fuels and releasing their stored carbon is a problem because the carbon cycle does not have enough carbon sinks to remove the excess carbon from the atmosphere. Fossil fuels take millions of years to form, and Earth’s carbon sinks cannot remove enough carbon dioxide to prevent it from building up in the atmosphere. The accumulation of carbon dioxide in the atmosphere is increasing Earth’s greenhouse effect.
storage and transmission centres, like this Google-owned one in Iowa, United States, operate continuously. They use a constant amount of energy, regardless of whether an email is sent or not.
A book published in 2010 popularised the idea that reducing the number of emails sent could have a significant impact on greenhouse gas emissions. The book stated that an average person’s yearly email use generates 3–40 kg of carbon dioxide and other greenhouse gases, which is comparable to driving 16–206 km. While deleting 1000 emails would save about 5 g of CO2, manually deleting them on a laptop for 30 minutes emits 28 g of CO2. This means that manually deleting emails can have a greater carbon impact than just storing them, because it consumes more energy from using the computer.
In reality, the carbon footprint of sending emails is difficult to quantify and the numbers change constantly due to improving data transmission and storage efficiency. The carbon values for emails seem small, and reducing the number of emails sent or deleting them may not significantly reduce energy consumption because digital data storage and transmission systems operate continuously. Instead, the carbon footprint of email use can be reduced by using electronic devices that consume less electricity and retaining them for as long as possible.
In 2023, the United Nations announced that it had created a new Global Greenhouse Gas Monitoring Infrastructure. The infrastructure will integrate space and Earth surface-based observation systems, and aims to provide real-time tracking of greenhouse gases to help inform policy choices. The platform will address uncertainties about the emission of greenhouse gases and provide faster and more accurate data on the state of the planet’s atmosphere. What are the advantages of this new infrastructure?
Reducing greenhouse gas emissions is essential for addressing the enhanced greenhouse effect. To achieve this goal, several strategies have been developed, each with advantages and limitations. These are listed in Table 7.7.
Method
Renewable energy sources
Description
Energy sources like solar, wind, hydro and geothermal that produce electricity without greenhouse gas emissions
Energy efficiency improvements Using less energy to perform the same tasks, e.g. by using improved appliances and building designs
Carbon capture and storage technology
Reforestation and afforestation
Sustainable agriculture
Policy and regulatory measures
Technology that captures CO2 emissions from industrial processes and stores it
Planting trees to absorb CO2
Farming practices that improve soil health and reduce greenhouse gas emissions, e.g. crop rotation and no-till farming
Government policies and regulations that set standards and provide incentives for reducing greenhouse gas emissions
Advantages
• Directly reduces greenhouse gases
• Creates jobs
• Quick implementation
• Encourages innovation
• Capable of largescale CO2 capture
• Supports biodiversity
• Prevents soil erosion
• Improves soil health
• Supports biodiversity
• Can promote largescale changes
Limitations
• Supply may be unreliable
• High initial costs
• Requires significant land
• High initial costs
• Expensive
• Risk of CO2 leakage
• Requires large land area
• Trees take time to mature
• Ongoing management required
• Lower short-term profits
• Requires education and training
• Political challenges
• Increased costs for businesses and individuals
• Requires international cooperation
Table 7.7 Strategies
Some of the strategies outlined in Table 7.7 involve capturing carbon dioxide from the atmosphere and storing it in long-term carbon sinks. This process is called carbon sequestration. Carbon sinks help to reduce the amount of carbon dioxide in the atmosphere.
Carbon is stored naturally in ecosystems in a number of ways, including the following:
• Forests – as trees grow, they absorb carbon dioxide from the atmosphere through photosynthesis, using it to build biomass. Trees store carbon in their trunks, branches, leaves and roots, where it remains for many years. Tropical rainforests are known for their high carbonstorage capacity due to their dense vegetation and high rates of photosynthesis.
• Oceans – the ocean can also absorb carbon dioxide directly from the atmosphere, and scientists estimate that it can absorb and store about 25% of the carbon dioxide released into the atmosphere by human activities. Colder water is more effective at dissolving and absorbing carbon dioxide than warmer water, so as the oceans warm up, they are becoming less efficient at absorbing carbon. As more carbon dioxide is taken up by the ocean, the water becomes more acidic, which is harmful to marine organisms.
• Soil – carbon sequestration in soil occurs through the process of photosynthesis, where plants take in carbon dioxide from the atmosphere and convert it into organic matter. When plants die, this organic matter is deposited in the soil, where it can be stored. Peatlands are particularly important ecosystems for carbon sequestration (see Figure 7.32), because large amounts of carbon can be stored in these soils.
carbon sequestration the process of storing carbon in a carbon sink
1. Recall why tropical forests can sequester more carbon than cold-climate trees.
2. Identify whether cold water or warm water is more effective at storing carbon dioxide.
Landcare is a community organisation that aims to improve the health of the land and waterways in Australia by promoting sustainable land use and management practices.
Established in the late 1980s, Landcare brings together farmers, landowners, natural resource managers and community members to collaborate on local projects that address issues such as soil erosion, water quality, biodiversity loss and carbon sequestration.
Figure 7.33 A Landcare-funded project led by Southern Forest Community Landcare is investigating the benefits of introducing dung beetles to south-western Australia. The Dung Beetle Ecosystem Engineers project aims to broaden the variety of dung beetles in the region and study their effectiveness for livestock producers.
Landcare is supported by the Australian Government, which provides funding and other resources. Landcare has become a widely recognised and respected initiative that has made a significant contribution to environmental sustainability in Australia.
Examine how government initiatives such as Landcare have supported the adoption of effective land restoration practices that improve soil quality and increase carbon sequestration in soils.
Try this 7.4
In your class, collaborate to prepare a written report for your local government on estimated carbon storage in different local ecosystems. Propose ways to increase carbon storage in your local area.
A variety of technologies are being developed for carbon capture. Once captured, the carbon dioxide can be compressed and transported to a storage or utilisation site where it can be used in a wide range of industries.
• Post-combustion capture: CO2 from flue gases is captured after fossil fuels are burned in power plants or industrial facilities.
• Pre-combustion capture: Fossil fuels are converted into a gas. The gas is then treated to remove CO2 before being burned.
• Oxyfuel combustion: Fossil fuels are burned in pure oxygen instead of air. The resulting gas is almost pure CO2, which can be readily captured.
• Carbon mineralisation: CO2 is reacted with certain types of minerals to produce stable carbonates. The carbonates can then be stored underground or used in building materials.
• Direct air capture: Machines directly capture CO2.
Once captured, carbon dioxide can be stored in a variety of ways.
• Geological storage: CO2 is injected into underground rock formations, such as depleted oil and gas reservoirs. In enhanced oil recovery, CO2 is injected into oil reservoirs to recover more oil. The CO2 is stored in the reservoir.
• Ocean storage: CO2 is injected into the ocean, where it can dissolve and be stored in the deep ocean.
• Mineral storage: CO2 is reacted with certain types of minerals to produce stable carbonates, which can then be stored underground.
Go online to access the interactive section review and more!
1. Recall some of the ways in which carbon dioxide can be stored once it has been captured.
2. Name the carbon capture technology that recovers more carbon dioxide by burning fuels in pure oxygen.
Online quiz
Section 7.3 questions
Remembering
1. Name three gases in the atmosphere that cause the greenhouse effect.
2. Define ‘carbon sequestration’.
3. State the name of the radiation emitted from the: a) Sun b) ground and oceans.
4. Recall the sources of methane in the atmosphere.
Understanding
5. Explain the differences between the natural and enhanced greenhouse effects.
6. Explain why the following statement is incorrect: ‘The greenhouse effect is caused by humans’.
7. Describe how enhanced oil recovery works.
8. Describe the consequences of ocean warming on ocean carbon sequestration.
Applying
9. Apply your understanding of the carbon cycle to explain how changes in land use, such as converting forests into farmland, can affect atmospheric carbon levels.
10. Draw a diagram to illustrate how the greenhouse effect keeps Earth warm.
Analysing
11. Compare short-wave radiation and long-wave radiation.
12. Distinguish between greenhouse gases and other gases in the atmosphere, such as nitrogen and oxygen.
13. Contrast carbon sinks and carbon sources by giving examples.
14. Contrast pre-combustion and post-combustion carbon capture.
Evaluating
15. Predict what conditions on Earth would be like without greenhouse gases and the greenhouse effect.
16. In relation to the enhanced greenhouse effect, decide why our focus is on carbon dioxide and not other greenhouse gases.
17. We have known about the damaging effects of carbon emissions for a long time. Propose why Australia still produces 70% of its electricity from coal.
18. Discuss the reasons why the carbon cycle is altered by the release of carbon emissions from burning fossil fuels.
19. Predict how global carbon sequestration will be affected if global warming continues.
At the end of this section, I will be able to:
1. Identify changes in global climate over time.
2. Explain the role that deep ocean currents play in global climate.
3. Describe the indicators of climate change.
The difference between weather and climate is the time frame. Weather is the conditions of the atmosphere in terms of temperature, cloud, rain and wind over a short period of time (minutes to months). The climate of an area is how the area behaves over a much longer period of time, usually 30 or more years. Different areas can have different climates; for example, the climate in Western Australia is very different from the climate in Tasmania.
The western coast of Australia experiences more storms in summer due to a weather pattern known as the West Coast Trough. This trough is a low-pressure system that forms along the western coast, especially during the warmer months, bringing heavy rainfall and strong winds. The formation of the West Coast Trough is influenced by warm ocean temperatures, high-pressure systems, and the unique coastal topography of the region. These conditions create the energy and moisture necessary to fuel intense storms, making the area particularly susceptible to severe weather events during the summer season.
The Sun’s radiation is absorbed by the ocean, particularly in tropical waters. The ocean plays a critical role in Earth’s climate system because it doesn’t just store heat, it also distributes it around the globe through the water cycle.
Evaporation is a key component of this heat exchange. When ocean water absorbs the Sun’s radiation, it heats up and evaporates into the atmosphere, leading to an increase in temperature and humidity. This increased humidity then condenses into clouds, which can lead to stormy weather. Storms are carried by trade winds and travel long distances, distributing heat and moisture around the Earth. This exchange of heat and moisture between the ocean and the atmosphere helps to regulate the global climate.
Deep ocean currents play a significant role in driving weather patterns, especially in areas away from the equator. Ocean currents are influenced by a complex interplay of factors, including wind, temperature gradients, salinity, Earth’s rotation and tides. They help regulate global temperature by transporting heat from the equator to the poles (see Figure 7.37). This transfer of heat helps distribute the warm equatorial waters to the colder polar regions, making the temperature differences between the two areas less extreme.
By distributing heat, ocean currents can affect local and regional climates, and they play a major role in the global climate system. Deep ocean currents also mix water and nutrients from the ocean’s surface to its depths. This process supports the overall health and productivity of oceanic ecosystems by ensuring the availability of essential nutrients for marine life. The movement of these nutrients plays a critical role in nutrient cycling, connecting the hydrosphere and the biosphere, and contributing to the balance of life in ocean ecosystems.
Quick check 7.18
1. Define the term ‘weather’.
2. Describe how deep ocean currents regulate global temperatures.
Figure 7.37 The most well-known deep ocean current is the thermohaline circulation, also known as the ‘global conveyor belt’. This current is driven by differences in water temperature and salinity (haline), which affect water density. Warm water from the tropical regions flows towards the colder North Atlantic, releasing heat into the atmosphere, and then returns as cold, dense, salty water to the equatorial regions to begin the cycle again. This heat- and salt-driven exchange significantly affects the climate of regions far from the equator, helping to distribute heat over Earth’s surface and contributing to a more stable global climate.
Earth’s climate is dynamic and has undergone significant changes over time. In the past, Earth has experienced many ice ages, where the planet was far colder than it is today, as well as warmer periods, when temperatures were higher than they are today.
A glacial period is when a reduction in global temperatures is sustained for a long period of time. The last glacial period started around 115 000 years ago and ended around 11 700 years ago. During this period, sea levels were much lower than now, due to the presence of vast ice sheets. As a result, it was possible to walk from Tasmania to mainland Australia across a land bridge. However, as sea levels rose, the land bridge was submerged, creating the Bass Strait.
Figure 7.38 Earth has undergone natural cycles of warming and cooling.
glacial period a period in Earth’s history when a reduction in global temperatures is sustained for a long period of time
interglacial period a period in Earth’s history when an increase in global temperatures is sustained for a long period of time anthropogenic caused or influenced by humans
We are currently experiencing an interglacial period, and Earth’s climate has remained relatively stable throughout this period, with only small fluctuations. However, the current rate of global warming is much faster than the natural climate change observed in the past and is being caused by human activities. This is known as anthropogenic climate change.
Figure 7.39 The changes in energy balances, such as the burning of more fossil fuels, have contributed significantly to global climate change. The Keeling curve shows the concentration of carbon dioxide in parts per million (ppm) from 1958 to 2024 using measurements taken from an observatory in Hawaii. The concentration of carbon dioxide in the atmosphere has increased from 280 ppm before 1800 to well over 424 ppm in 2024.
Anthropogenic climate change is linked to the burning of fossil fuels, deforestation and industrial processes. The release of greenhouse gases, such as carbon dioxide, methane and nitrous oxide, into the atmosphere is the primary cause of this accelerated climate change. These gases trap heat from the Sun in Earth’s atmosphere, leading to a faster warming of the planet. Over the past 100 years, Earth’s average temperature has risen between 0.4°C and 0.8°C; 2016 was the hottest year and 2019 was the second-hottest since records began. The years since 2014 have been the warmest years on record.
Figure 7.40 Australia’s environmental protection efforts continue to be rated among the lowest in the world. Australia ranks 52nd out of 63 possible places in the Climate Change Performance Index 2025.
Beef and dairy cattle contribute significantly to climate change through the following processes.
• Methane emissions. Cows produce methane through a digestive process known as rumination.
• Land use change. Beef and dairy production often requires the conversion of natural habitats, such as forests and grasslands, into agricultural land for growing feed crops and for pasture. This conversion leads to the loss of carbon-absorbing vegetation and soil, and releases carbon into the atmosphere.
Figure 7.41 Most methane from cows is emitted through their burps, although some comes from flatulence. In 2022, a design group called Zelp (Zero Emissions Livestock Project) won a design competition for creating a cow mask that converts methane emissions into CO2 and water vapour.
• Fertiliser use. Growing crops to feed cattle requires the use of fertilisers, which produce nitrous oxide.
• Transportation emissions. Beef and dairy products are often transported long distances, contributing to emissions from transportation.
Quick check 7.20
1. Name three greenhouse gases.
2. Recall the main greenhouse gas produced by agriculture.
To better understand the impacts of climate change and track progress in mitigating its effects, scientists use a variety of consequences of climate change as indicators to monitor changes in the climate system. These indicators provide a picture of the state of the climate.
Ocean and atmospheric temperatures reflect the overall temperature of the planet’s surface. Any long-term increase in atmospheric and ocean temperatures will affect many aspects of Earth’s systems, including ocean circulation, sea level and weather patterns, leading to climate change. Rising temperatures result in increased rainfall, the melting of glaciers and ice sheets, and rising sea levels. Increased temperatures in the atmosphere result in more energy being available to create extreme weather events such as storms and cyclones. Temperature changes are monitored by a variety of instruments, including satellite measurements, ocean buoys and weather stations, providing evidence for climate change and the ongoing impact of human activities.
As global temperatures increase, ice caps melt and cause a rise in sea levels. Ocean water in equatorial regions expands as it warms, contributing to further rises in sea levels. Increasing sea levels can cause coastal flooding and erosion, and affect coastal ecosystems and communities. Sea level measurements are made using equipment such as satellite altimeters and tide gauges.
Did you know? 7.3
la niña events are getting worse
La Niña is a climatic phenomenon characterised by the cooling of the central and eastern tropical Pacific Ocean. It is the counterpart to El Niño, which is characterised by warming of the same region. La Niña events can have significant impacts on global weather patterns, causing alterations in temperature, precipitation and wind patterns.
Some of the effects of La Niña include increased rainfall in some areas, drought in others and changes in atmospheric circulation patterns that can affect tropical storms. La Niña is one of the important factors that scientists consider when making long-range weather and climate forecasts.
7.4
La Niña events are a natural part of Earth’s climate system, but their severity and frequency may be influenced by climate change, as rising global temperatures can disrupt the balance of ocean and atmospheric conditions that drive these events.
Figure 7.45 La Niña typically increases the chance of above-average rainfall for northern and eastern Australia during summer. The impact of the 2022 La Niña on rainfall in Australia was exacerbated by the warming of the Indian Ocean, which has been attributed to human-caused climate change. This warming is likely to have contributed to record rainfalls and devastating floods.
When seawater freezes in winter, only the water freezes – the salt is left behind in the unfrozen seawater below. Waters with higher concentrations of salt are denser and sink to the ocean floor. Different densities are the main cause of ocean currents, circulating seawater from the sea floor to the surface and all around the globe. This water carries with it thermal energy, organic matter and nutrients.
With rising temperatures, less seawater is freezing, which is reducing the density of the oceans. If seawater circulation slowed, and organic matter and nutrients also stopped circulating, the impact on the survival of marine life would be huge.
Aim
To determine how the concentration of sodium chloride in water (salinity) affects its density.
Materials
• 10 mL measuring cylinder
• 100 mL measuring cylinder
• 5 × 100 mL beakers
• 5 pipettes
• food colouring (blue, green, yellow and red)
sodium chloride
warm water
weighing boats
balance
Method
1. Copy the results table into your science journal.
2. Using a 100 mL measuring cylinder, measure 60 mL of water and pour it into one of the 100 mL beakers. Repeat four more times so you have five beakers each with 60 mL of water. Label the beakers 1 to 5.
Table showing contents of beakers 1 to 5
3. Add the required drops of food colouring from the table above to each beaker.
4. Using the weighing boats and balance, measure the five different masses of sodium chloride. Pour the sodium chloride into the correct-coloured beaker.
5. Stir the solutions to make sure all the sodium chloride has dissolved.
6. Using a pipette, draw up 2 mL of solution 5 and add to the 10 mL measuring cylinder.
7. Using a pipette, draw up 2 mL of solution 4. Place the pipette along the inside of the measuring cylinder, near the solution added previously. Drop solution 4 drop by drop, allowing it to roll down the side of the measuring cylinder.
8. Repeat step 7 for solutions 3, 2 and 1, adding each in turn to the 10 mL measuring cylinder.
Results
1. Complete the results table. Remember that 1 g water = 1 mL water.
Table showing mass of sodium chloride in solution and density of solution
2. Sketch a coloured diagram of the measuring cylinder you created.
3. Plot a graph of mass of sodium chloride on the x-axis and density on the y-axis.
Discussion
1. Use your graph to describe the link between amount of sodium chloride and the density of a solution.
2. Discuss how rising global temperatures affect the concentration of sodium chloride in the oceans and how this relates to climate change.
Conclusion
1. State a conclusion about how water salinity affects water density. Support your statement by using your experimental data.
Biodiversity and species distribution
Climate change is one of the biggest threats to global biodiversity. It can alter the distribution and abundance of species, leading to changes in the composition and structure of ecosystems. Rising temperatures can shift the ranges of species and alter their migration patterns, disrupt the timing of seasonal events such as flowering and migration, and change the distribution of disease-causing organisms.
Climate change has led to shifting climatic zones, resulting in species moving towards the poles and to cooler, higher elevations on land and deeper ocean waters for some marine species. In Western Australia, for example, marine species such as tropical fish are appearing further south along the coast as ocean waters warm. On average, species are moving towards the poles at 17 km per decade on land and 78 km per decade in the ocean.
7.46 Blue dragons (Glaucus atlanticus) are small venomous sea slugs found in warm and temperate waters. As ocean temperatures continue to increase, the distribution of blue dragons is expanding. While some species may benefit from climate change in the short term, the long-term effects are often negative and can lead to declines in biodiversity.
Different species are responding to climate change at different rates, leading to changes in the structure of ecosystems. As species move to new locations, they interact with species they may have never encountered before, forming new ecological communities. At the same time, species that had previously relied on each other for food or shelter may be forced apart, disrupting established ecological relationships and potentially leading to ecosystems collapsing.
Explore! 7.10
Citizen science is scientific research in which the general public participate in collecting data. This can include monitoring wildlife populations, tracking the spread of invasive species or contributing observations to astronomical studies. The goal is to involve citizens in the scientific process, allowing the collection of large amounts of data that would normally be difficult.
Research the citizen science project Redmap to see how everyday Australians have documented species on the move around Australia’s coasts over the past decade and how this is contributing to our knowledge about climate change.
Figure 7.47 Australia’s volunteer tagging database Infofish Australia became the first citizen science tagging program in the world to tag one million fish. Over the past 36 years, over 17 000 taggers contributed over 198 600 days (or 544 years) of effort to reach the milestone.
Permafrost, or permanently frozen ground, is sensitive to temperature changes and can provide information about past and present climate conditions. Scientists are monitoring permafrost as it starts to melt as temperatures increase. When permafrost melts, it releases trapped carbon dioxide and methane, both of which are greenhouse gases. The presence, thickness and temperature of permafrost provide scientists with valuable information about the rate of climate change and the potential impacts of these changes.
As global temperatures increase, sea ice melts, and this has wide-ranging effects on global weather patterns, ocean currents and coastal communities. Sea ice is highly sensitive to changes in air and water temperature, making it an important indicator of climate change. The extent and thickness of sea ice in the polar regions provide scientists with valuable information about the rate of climate change, as a decrease in sea ice over time can signal a warming trend.
One significant process affected by this melting is the albedo effect, which refers to the reflectivity of Earth’s surface. Sea ice has a high albedo, meaning it reflects most of the incoming sunlight back into space, helping to regulate Earth’s temperature. As sea ice melts and exposes darker ocean water, which has a much lower albedo, more sunlight is absorbed instead of reflected, leading to further warming of the ocean and accelerating the ice melt in a positive feedback loop. This reduction in sea ice also affects ocean currents, particularly the thermohaline circulation, by altering temperature and salinity gradients.
Figure 7.48 The thawing of permafrost has significant impacts on the lithosphere and the biosphere. As permafrost melts, it releases stored carbon, mainly as methane and carbon dioxide, into the atmosphere. This release exacerbates the greenhouse effect, contributing to further warming and creating a feedback loop that accelerates permafrost thaw.
Figure 7.49 In the biosphere, the thawing and melting can release nutrients and promote the growth of plants, but it can also lead to the loss of critical habitats and biodiversity.
Disruptions to these currents can shift weather patterns globally, bringing about more intense storms, changes in precipitation and shifts in temperature. In coastal communities, the loss of sea ice and rising sea levels increase the risk of flooding, erosion and damage to infrastructure, threatening both human populations and ecosystems.
Figure 7.50 The changing climate affects migration patterns, breeding cycles and food availability for Arctic species. For example, earlier spring melts and later autumn freezes affect the availability of food for caribou, disrupting their life cycles and those of the indigenous communities that rely on them.
Figure 7.51 Climate change has contributed to longer and more severe bushfire seasons in Australia. The 2019–2020 ‘Black Summer’ bushfires, exacerbated by prolonged drought and high temperatures, devastated vast areas of forest and grassland, killing millions of animals and destroying their habitats.
Changing
Climate change has a significant impact on coral reefs, which are some of the most biodiverse ecosystems on the planet.
The main effects of climate change on coral reefs include:
• Ocean acidification. Increases in atmospheric carbon dioxide also increases the acidity of the oceans. This makes it more difficult for corals to build and maintain their calcium carbonate skeletons, leading to their degradation.
• Coral bleaching. Corals rely on symbiotic single-celled organisms called protists to provide their nutrition. As the temperature of the ocean increases, corals become stressed and expel the protists, leading to coral bleaching.
• Changes in ocean circulation. Changes in ocean currents caused by war ming of the ocean can affect the availability of food and nutrients for corals.
• Sea level rise. As the sea level rises, corals are increasingly at risk of being unable to grow vertically fast enough to maintain their depth at or below the surface. Living under the lower light conditions at greater depth will reduce their growth and threaten survival and increase their exposure to other stressors such as pollutants and disease.
These impacts of climate change on coral reefs will also have consequences for the millions of people who rely on them for food, income and coastal protection.
Research some of the reasons why coral bleaching is disastrous for the environment.
1. State one indicator that scientists can use to monitor climate conditions.
2. Identify the main problem of melting polar ice caps.
3. Identify the problem caused by decreased ocean density as a result of reduced freezing of ice in winter.
Try this 7.5
Make an infographic
Create a digital infographic to highlight the multiple lines of evidence from polar ice caps, ocean temperatures and extreme weather that explain how climate change is impacting Earth.
Your infographic should:
• communicate information concisely
• be visually appealing, with good use of colour and images
• be well organised so viewers can easily see the information
• contain relevant data from credible sources.
Go online to access the interactive section review and more!
Section 7.4 review
Online quiz
Section 7.4 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. Name two indicators of climate change.
2. Recall what permafrost is.
3. Identify the reasons why coral bleaching is so disastrous for an environment.
4. Define the term ‘climate’.
5. Identify the correct words to complete the following sentence: Earth is currently experiencing an interglacial / a glacial period.
6. State one way that humans have influenced the climate on Earth.
Understanding
7. Describe how permafrost can be used as an indicator of climate change.
8. Describe some differences in climate between New South Wales and Western Australia.
9. Describe the relationship between global temperatures and the glacial and interglacial periods.
10. Explain the impact that deep ocean currents have on global climate.
Applying
11. As part of a citizen science project, you are collecting data on species distribution. Identify how you could you use this data to further our understanding of how climate change is affecting biodiversity.
12. Design a climate action plan for a region facing severe deforestation and high greenhouse gas emissions from agriculture and fossil fuel use.
Analysing
13. Critique the following statement: ‘Global warming will not affect biodiversity’.
14. Compare global warming and climate change.
15. Differentiate between weather and climate.
Evaluating
16. Discuss how global warming could cause sea levels to rise.
17. Discuss why less seawater freezing in winter affects ocean currents.
18. Discuss how human activities have accelerated climate change.
19. Evaluate the effect of an unexpected volcanic eruption on climate change predictions.
At the end of this section, I will be able to:
1. Describe how we can collect data and predict changes to the Earth system.
2. Identify strategies used to reduce climate change or mitigate its impacts.
Being able to predict changes to the Earth system is an important part of preparing for the impacts of climate change. This involves collecting data and then using modelling and simulations to understand how Earth’s climate and ecosystems are changing and will change in the future, given certain assumptions. The models consider the complex interactions between Earth’s spheres and provide information about how the Earth system is likely to respond to various scenarios.
Scientists use satellites to produce global data about ocean temperatures, sea levels, and forest and ice cover. Different properties of Earth’s surface and atmosphere can be measured to provide a continuous stream of data that is used to monitor global climate changes.
To measure ocean temperatures, satellites use radiometers that can detect infrared (heat) and microwave radiation emitted by the ocean surface. This radiation is proportional to the temperature of the surface, so the data can be used to create maps of ocean temperature patterns.
Sea level data is generated by satellite altimeters (see Figure 7.55), which use radar to measure the height of the ocean surface relative to a reference point, providing information on the rise or fall of sea levels over time.
Satellites also use optical and microwave sensors to monitor changes in forest and ice cover. These instruments can detect changes in the reflection and emission of radiation from Earth’s surface, which indicate the amount of vegetation or ice present. This data can be used to track deforestation and the rate of ice melting.
Figure 7.56 The two-satellite mission Copernicus Sentinel-2 has produced before and after photos of the ice slab that broke away from the Brunt Ice Shelf, Antarctica. The image on the left shows cracks on the ice shelf on 25 October 2022 and the image on the right shows the ice breaking away on 23 January 2023.
The data generated by satellites is used to monitor the effects of climate change by providing a record of changes over time.
Predicting changes to the Earth system is a challenging task, as it involves understanding and representing many complex processes and their feedback, over a wide range of timescales.
Computer modelling has improved our knowledge and our ability to predict how phenomena such as climate change and atmospheric pollution will develop in the future. Computer simulations can be used to make predictions about Earth’s climate thousands and millions of years into the future, to see what impact actions taken now will have on the climate in the future. With their huge processing power, computers can run numerous simulations repeatedly in a short time, something that could take a human over a lifetime to complete. By running numerous simulations, predictions made by computer modelling are much more accurate than those made manually by humans.
Table 7.8 lists some of the applications of computer modelling.
Application of computer modelling
Predicting the weather
Predicting climate change
Predicting pollutant effects
Table 7.8 Some of the applications of computer modelling
Description
You will see this used every day if you watch the news. Multiple simulations are run by computers. Meteorologists (scientists who study the weather) use these simulations to predict the weather conditions for that week (and beyond).
Models predicting climate change are based on observational data and fundamental physical laws such as Newton’s laws. Perhaps the most complex climate models are the general circulation models (GCMs). Data on climate change reported in the media is generated from numerous simulations of the GCMs.
Atmospheric dispersion modelling predicts the behaviour of pollutants in the air over a specific period of time. It is used by governments to monitor air quality and to predict the effects of chemical spills.
Rapidly emerging quantum computers will be able to enhance the modelling of complex weather and climate systems by using quantum algorithms to perform simulations that are beyond the reach of classical computers. Unlike classical computers, which store and process information using binary bits that are only in one of two states (0 or 1), quantum computers use quantum bits (qubits), which exist in multiple states simultaneously. This allows quantum algorithms to perform certain tasks such as simulations much more quickly than classical algorithms.
These simulations will help improve our understanding of how weather patterns and climate interact and change over time, allowing more accurate forecasting and prediction of weather patterns and the impacts of climate change. Quantum computers will be able to process large amounts of data more quickly and efficiently, enabling more detailed simulations.
Even though there is scientific consensus that climate change is real and is largely driven by human activities, there is still some uncertainty about how things will change in the future. This uncertainty leads to the use of different models and approaches to predict the impacts of climate change based on different scenarios.
Each climate change model uses different assumptions and has different limitations. Models are limited by the amount and quality of input data, and by the fact that real-world processes are subject to complex and random events that lead to unpredictable variations. As a result, models produce different projections of how the climate will change in the future. To address this uncertainty, scientists use multiple models. Using multiple models gives a more comprehensive understanding of the potential impacts of climate change and helps guide governmental decision-making about how to mitigate its effects. As more data is collected and our understanding of climate change improves, new models are continually being developed and refined.
Climate change denial is the rejection of the scientific consensus on the reality, causes and potential impacts of global warming, despite overwhelming evidence. Climate change models are contested by some people in society for various reasons, including political, economic and ideological motivations. Some people may question the validity of climate change models because they challenge their long-held beliefs or economic interests. Others may be sceptical of scientists and question the impartiality and accuracy of the data and methods used to develop climate models. There is also a belief among some people that the models are too complex and that their predictions are unreliable. These people may also reject the idea of human-caused climate change altogether, and therefore not accept the projections produced by climate change models. Misinformation about climate change has also played a role in contesting the models. Some individuals deliberately spread false information or manipulate data to discredit the models and cause people to doubt the science of climate change.
One common method of data manipulation involves altering graphs to support a specific agenda. In climate change debates, this tactic can be used to downplay or exaggerate the impacts of global warming. Some techniques used are outlined here.
• Adjusting the scale of the axes can make trends appear more or less dramatic (see Figure 7.59). For example, a temperature rise that is relatively small might be made to look significant by using a very narrow y-axis range.
• Presenting data from a limited time frame can mislead viewers about long-term trends. For example, displaying a short period of stable temperatures might suggest that climate change is not occurring, even though longer-term data indicates significant warming.
• Selecting specific data points that fit a desired narrative while ignoring others can skew the perceived trend. For example, focusing on a few cold years in a generally warming trend can give the false impression that global temperatures are decreasing.
Figure 7.59 Graph of atmospheric carbon dioxide levels over time. The data used is the same in both graphs, but in (a) the y-axis begins at 300 ppm, and in (b) the y-axis begins at 0 ppm. The increase in CO2 in (b) looks less steep than in (a)
While some contest the models, most climate scientists agree that the models provide valuable insights into the future of the climate and are an essential tool for understanding the impacts of human activities on the planet.
1. Generate a list of viewpoints that individuals belonging to different groups in society could hold regarding climate change (e.g. farmers, politicians, climate scientists).
2. Select one of the viewpoints to consider, using the following statements:
• I am considering climate change through the viewpoint of ... [insert the selected viewpoint].
• I believe ... [describe the subject matter from the chosen viewpoint]. Assume their character.
• A query that arises from this perspective is ... [pose a question from the chosen viewpoint].
In your class, you may then want to engage in an evidence-based debate about the role of human activity in global climate change.
The Circle of viewpoints thinking routine was developed by Project Zero, a research centre at the Harvard
1. Explain why scientists use computer modelling to predict phenomena.
2. State one application of computer modelling.
3. Describe how quantum computers will enhance climate modelling.
4. Explain why computer models are not perfect.
5. State some reasons why people contest climate change models.
Climate change is a significant global challenge that is affecting the planet in many ways, from rising temperatures and sea levels to extreme weather events and changing ecosystems. Research how the following strategies reduce climate change or mitigate its effects:
• Reducing greenhouse gas emissions
• Carbon capture and storage
• Reforestation and forest preservation
• Sustainable agriculture
• Energy conservation
• Public and active transportation
• Carbon pricing.
Carbon farming refers to a set of land management practices that aim to reduce greenhouse gas emissions from agriculture and other land uses while improving the health and productivity of ecosystems. The aim of carbon farming is to sequester (store) carbon in soil and vegetation to reduce atmospheric carbon dioxide.
Traditional Owners are implementing carbonfarming practices that support the management and restoration of natural ecosystems while also mitigating the effects of climate change. Communities are using their traditional knowledge of the land to implement reforestation projects, which not only restore forests but also sequester carbon and therefore reduce the effects of climate change. They are also using traditional land management practices, such as controlled burning, to reduce greenhouse gas emissions and improve ecosystem health.
The Aboriginal Carbon Foundation is a non-profit organisation run by Aboriginal and Torres Strait Islander people that provides carbon farming services. The foundation was established in 2010 with the primary aim of promoting sustainable land management practices that reduce greenhouse gas emissions while also generating economic benefits for Indigenous communities.
Section 7.5 review
Online quiz
Go online to access the interactive section review and more! Section questions
Section 7.5 questions
Remembering
1. Name the complex models used to make predictions about climate change.
2. Recall why quantum computers will be able to process more information than classical computers.
3. Recall how satellites measure sea levels.
Understanding
4. Explain why computer models are useful in predicting future events.
5. Describe one strategy that can be used to mitigate (reduce) the impacts of climate change.
Applying
6. Identify the advantages of using satellites to collect data about global climate.
Analysing
7. Critique the following statement: 'Global climate models are perfect.’
Evaluating
8. Discuss the reasons why some people might not believe climate change is occurring.
Chapter checklist
Success criteria Linked questions
7.1I can distinguish between Earth's chemical spheres: atmosphere, biosphere, geosphere and hydrosphere. 2, 20
7.1I can explain that the Sun's radiation and its interactions with Earth's spheres are the foundation for the global climate system. 3, 11
7.2I can describe the carbon cycle. 9, 17, 18
7.2I can describe the water cycle. 8
7.2I can describe the role of cultural burning in facilitating energy and nutrient transfers. 15
7.2I can identify the impact of human activity on local freshwater availability.28
7.3I can describe the greenhouse effect and relate it to the role carbon dioxide plays in maintaining temperatures that support life on Earth. 1, 10, 11, 14
7.3I can describe the impact of human activity on the carbon cycle.12
7.3I can describe strategies that can reduce carbon dioxide emissions.13
7.3I can identify how carbon dioxide is captured and stored naturally or through the use of technologies. 29
7.4I can identify changes in global climate over time. 6, 16
7.4I can explain the role that deep ocean currents play in global climate.7
7.4I can describe the indicators of climate change. 22
7.5I can describe how we can collect data and predict changes to the Earth system. 23
7.5I can identify strategies used to reduce climate change or mitigate its impacts. 26
Review questions
Remembering
1. Most of the Sun’s radiation that reaches Earth is absorbed by the ground and oceans. Recall what happens to the rest of the Sun’s radiation.
2. State the four global spheres.
3. Recall the foundation for the global climate system.
4. Identify the most abundant greenhouse gas.
Understanding
5. Describe the effects of cyclones on each of Earth’s chemical spheres.
6. Explain why it was once possible to walk from Tasmania to Victoria.
7. Describe a potential impact of changes in deep ocean currents on global climate patterns.
8. Describe how water moves between the atmosphere, land and oceans.
9. Explain how decomposition contributes to the carbon cycle.
10. Describe the natural greenhouse effect.
11. Describe what happens to long-wave radiation emitted from the ground and oceans.
12. Describe the impact of deforestation on carbon emissions.
13. Describe some strategies that can reduce carbon dioxide emissions.
14. Describe the role carbon dioxide plays in maintaining temperatures that support life on Earth.
15. Describe the role of cultural burning in facilitating energy and nutrient transfers.
Applying
16. Construct a graph to show how carbon dioxide concentrations have changed over the past two decades.
17. Construct a word equation to show how the process of photosynthesis leads to a decrease in atmospheric carbon dioxide.
18. Create a diagram to illustrate the carbon cycle.
Analysing
19. Copy and complete the following table to contrast the ozone layer and greenhouse gases.
Ozone layer Greenhouse gases
Function
Location
20.
21. Analyse the changes in carbon dioxide concentration in the atmosphere since the Industrial Revolution.
22. Identify the reason why low-lying areas are most at risk from climate change.
23. Discuss the advantages of using satellites to collect data about the global climate.
24. There is debate as to whether climate change is a significant risk to life on Earth. Decide whether you agree, based on what you have learned in this chapter. Justify your opinion with facts and evidence.
25. When scientists observe a change in the frequency of extreme weather events, they hypothesise the cause from scientific models. Evaluate the following hypothesis: If the El Niño weather pattern occurs more frequently, then there will be more droughts due to decreased rainfall.
26. Discuss which of the following strategies would be the most successful in your home town in terms of mitigating climate change. Give reasons for your answer.
Stategy 1: Reduction of greenhouse gas emissions
Stategy 2: Carbon capture and storage
Stategy 3: Reforestation and preservation
Stategy 4: Sustainable agriculture
Stategy 5: Energy conservation
27. Discuss what scientists can learn from understanding how the spheres of Earth interact with each other.
28. Evaluate how climate change might influence the water cycle and water resources in the future.
29. Evaluate the role of forests in carbon sequestration.
The graph in Figure 7.64 shows the distribution of organic carbon in different types of ecosystems, in the soil and in plant biomass above and below the ground.
Above- and below-ground biomass
Top soil
Subsoil
Figure 7.64 The total mass of organic carbon stored in different types of ecosystems, distributed between plant biomass, topsiol and subsoil.
Apply
1. Identify the type of forest that stores the most carbon in its soil.
2. Determine the ecosystem that has approximately half the organic carbon in the soil compared to the soil in the cool temperate moist ecosystem.
3. Determine the approximate mass of organic carbon found in the plant biomass of a tropical moist ecosystem.
Analyse
4. Identify any general relationship in the data.
5. Sequence the following ecosystems in order of total carbon mass, from most to least: boreal moist, polar dry, tropical dry, warm temperature moist, cool temperate dry.
Interpret
6. Can the data in Figure 7.64 be used to justify the following statement? ‘Tropical ecosystems sequester more carbon.’
As people become more aware of the impact of climate change, there is increasing interest in reducing our carbon footprint in every aspect of our lives. A carbon-neutral home is designed and built to minimise its carbon footprint and environmental impact – this means that the house produces zero net greenhouse gas emissions. Carbon-neutral homes are becoming increasingly popular as people look for ways to reduce their impact on the environment while still enjoying the benefits of modern living. In this activity, you will explore the concept of carbon-neutral homes and design your own carbon-neutral house.
Design a carbon-neutral house that meets the needs of a modern family while minimising its carbon footprint.
As an architect, you are part of a team of house-building professionals that includes engineers, policymakers and environmental researchers. Your team has been given the task of designing a carbon-neutral home that meets the needs of a modern family while minimising its environmental impact. This requires an understanding of environmental design principles, sustainable building materials and renewable energy sources.
To design a carbon-neutral home, you must first consider the energy required to heat and cool the home and power appliances and electronics. You must also consider the energy required to produce the building materials used in the construction of the home.
Singapore
One of the key components of a carbon-neutral home is incorporating renewable energy. This can include solar panels, wind turbines and geothermal systems. By using renewable energy technology, the home can produce its own energy, reducing the need for energy from traditional power sources that produce greenhouse gas emissions.
Another important consideration is the use of water. Water-efficient fixtures and appliances can help reduce water usage, which can help minimise the environmental impact of the home. Additionally, rainwater harvesting systems can help reduce the amount of water required from traditional sources.
You should also consider the materials used to construct the home. Sustainable building materials, such as bamboo, straw bales and recycled materials, can help reduce the carbon footprint of the home. The use of locally sourced materials can help reduce the energy required to transport building materials to the site.
To ensure the home is carbon neutral, it is also important to consider the landscaping surrounding the home. The use of native plants, which require less water and maintenance, can help reduce the environmental impact of the landscaping. Additionally, permeable paving and other sustainable landscaping techniques can help reduce water usage and run-off.
• graph paper or digital design software
• rulers, pencils, erasers and other drafting tools
• access to internet for research
1. Conduct some research and compare the carbon footprints of different types of homes, such as single-family homes, apartments and tiny homes.
2. In small groups, brainstorm ideas for what features a carbon-neutral house might have. Some examples are shown in Figures 7.66–7.68. Some suggestions are:
• solar panels or other renewable energy technologies
• insulation and energy-efficient appliances
• water-efficient fixtures and appliances
• low-impact building materials
• sustainable landscaping.
3. Once your group has developed a list of potential features, conduct some research on each idea to determine its feasibility and effectiveness. You should also research the costs associated with each idea.
4. Using graph paper or digital design software, design a floor plan and elevation for your carbonneutral house. You should incorporate the ideas that you have researched and consider how each feature will work to minimise the house’s carbon footprint.
5. Work with other groups in your class to design a community of carbon-neutral houses, considering factors such as shared resources and transportation options.
6. Reflect on what you have learned and how you might apply these concepts to your own lives.
7. As a class, discuss the challenges and benefits of designing a carbon-neutral house.
Figure 7.66 The BedZED housing development in London. BedZED (Beddington Zero Energy Development) was the UK’s first carbon-neutral ecocommunity. The buildings are constructed of materials that store heat when conditions are warm and release it when it cools down. Where possible, natural, recycled or reclaimed materials were used.
7.67
Houses are a revolutionary type of housing that combines advanced 3D printing technology with sustainable and locally sourced materials. They are printed by a 3D printing technique called Crane WASP, in which a large robotic arm deposits layers of natural materials, such as clay and rice husks, to create the house. The process is highly efficient and can complete a house in a matter of days.
Figure 7.68 The Waste House in Brighton, UK, is a sustainable building made entirely out of waste materials, including old toothbrushes, bicycle inner tubes, and DVD cases. It was designed and built by the University of Brighton’s Faculty of Arts and Architecture, and demonstrates the potential of ‘closed loop’ architecture, where waste is repurposed and reused in construction. The house has solar panels, rainwater harvesting systems, and other energy-saving features.
In this chapter, you will study the wave model of energy transfer. You will explore light and sound, both situations where energy is transferred by waves. You will take a look at the human eye and learn how light interacts with the structures in the eye to produce signals that our brain interprets as images. This chapter also explores how fast sound travels, and how sound waves interact with your eardrums, sending signals to your brain to be processed.
Section 8.1
Section 8.2
Section 8.3
Waves transfer energy
Electromagnetic waves Sound waves
Electromagnetic spectrum:
• Radio waves
• Microwaves
• Infrared radiation
• Visible light
• Ultraviolet light
• X-rays
• Gamma rays
Sensed through our ears
Corrective technology for hearing loss
Described through:
• Pitch
• Loudness
Can be Refracted
Sensed through our eyes Reflected
Corrective technology for vision loss
Shapes of lenses:
• Rectangular prisms
• Concave
• Convex
Shapes of mirrors:
• Flat
• Concave
• Convex
Curriculum content
Sound waves are longitudinal waves produced by vibrating objects; sound waves travel through solids, liquids and gases at different speeds; sound is reflected when coming into contact with a solid or liquid surface
• exploring why we see lightning before we hear thunder even though they occur at the same time
• exploring resonance and its applications, such as musical instruments, shattering glass and bridge design
• exploring echoes and their applications, such as echolocation in nature, ultrasound in medicine, depth sounding in oceanography and seismic surveying in mineral and oil exploration
• exploring the energy transfers that occur as sound travels through the ear and to the brain, and hearing conditions, such as conductive and nerve deafness
Light is an electromagnetic wave; light is made up of photons that have both particle and wave properties; light can be reflected from plane and curved mirrors and refracted when passing through concave and convex lenses
• exploring the refraction of light as it passes from one medium to another 8.2
• investigating the size, nature and position of images formed by plane and curved mirrors, concave and convex lenses
• pathway of light entering the eye and focusing on the retina and corrections for eye defects, such as short sightedness, long sightedness, astigmatism and cataracts
Collaborating and applying
Illustrate how advances in scientific understanding often rely on developments in technologies and engineering and technological and engineering advances are often linked to scientific discoveries
• exploring Australian technological advances, such as the cochlear implant pioneered by Professor Graeme Clark and the Monash Vision Group’s work on a bionic eye 8.1
Illustrate how proposed scientific responses to contemporary issues may impact on society
• considering safe sound levels for humans and implications in the workplace and leisure activities 8.3
© School Curriculum and Standards Authority
accommodation
amplitude angle of incidence angle of reflection
auditory nerve ciliary muscle
choroid cochlea
compression concave convex cornea crest cycle
displacement ear canal eardrum
electromagnetic radiation electromagnetic wave fovea frequency gamma ray
hertz incident ray infrared radiation ionising radiation iris lens lens (eye) longitudinal wave long-sighted mechanical wave
medium microwave normal optic nerve oscillating period periodic motion photon pitch plane mirror prism pupil
radio wave rarefaction
reflect reflected ray
refraction
refractive index
resonance frequency
retina
sclera
seismic wave self-propagating short-sighted transverse wave trough ultraviolet light
vacuum visible light
vitreous humour
wave wavelength X-ray
wave
a carrier of energy that travels through space or matter without the movement of matter as a whole
medium
the matter through which a mechanical wave travels
mechanical wave
a disturbance in a medium that transfers energy through that medium
electromagnetic
wave a wave with electric and magnetic components that can travel through matter or a vacuum
vacuum
At the end of this section, I will be able to:
a space completely devoid of matter
periodic motion the movement of a particle or an object that returns to its starting position and repeats in the same time interval, like a swing
1. Distinguish between mechanical and electromagnetic waves.
2. Label the amplitude and wavelength of a transverse and longitudinal wave.
3. List the types of electromagnetic radiation.
4. Label the compressions and rarefactions in longitudinal waves.
During a lightning storm, light and sound energy are transferred as waves. When you see lightning, your eyes detect light waves, and when you hear thunder, your ears detect sound waves. We see the lightning before we hear the thunder because light waves travel faster than sound waves.
A wave is a carrier of energy that travels through space or matter without the movement of matter. Some waves require matter, known as the medium, to move through. These are called mechanical waves. Sound and water waves are examples of mechanical waves. They create a disturbance in the medium that transfers the energy without the matter moving as a whole.
Another kind of wave, called an electromagnetic wave, can travel through matter but can also travel without a medium, through a vacuum. Visible light and radiant heat are examples of electromagnetic waves.
Mechanical waves transfer energy from the source of the wave (a force that starts the disturbance in the medium). The medium can be in any state – solid, liquid or gas – as long as there are particles present. In mechanical waves, a disturbance in a medium results in the transfer of energy by the vibration or periodic motion of particles.
Therefore, mechanical waves require particles of matter for the energy to travel through. These particles do not move along the wave; they only transfer the energy of the disturbance to the particles next to them. For example, a fishing float will bob up and down in the water as a ripple passes, revealing the periodic motion of the water particles, but it returns to its original position – it does not travel with the wave (see Figure 8.2). Depending on how the particles of the medium move relative to the direction of energy transfer, a mechanical wave can be classified as a transverse, longitudinal or surface wave.
8.2 As a ripple passes through the medium (water), the fishing float is temporarily displaced as it bobs up and down, before returning to its original position.
WORKSHEET
Wavelength, frequency and amplitude
Quick check 8.1
1. Define ‘mechanical wave’.
2. Identify the medium of a mechanical wave.
3. List three types of mechanical waves.
A transverse wave is a wave in which the disturbance of the medium is at right angles to the direction of energy transfer (see Figure 8.3).
Transverse wave in a rope
The up-and-down motion of the rope is perpendicular to the direction of the wave.
of energy transfer
Figure 8.3 In a transverse wave the particles move perpendicular (at right angles) to the direction of the energy transfer.
In mechanical transverse waves, the particles vibrate up and down, about their rest position, creating a series of crests and troughs. Crests and troughs represent the maximum displacement of a particle in the medium at the top and bottom of the wave respectively. The time taken for a wave to complete one cycle is called the period.
Three measurements describe the dimensions of a wave: frequency, wavelength and amplitude. The number of cycles of a wave per second is called the frequency and is measured in hertz (Hz). The distance measured in metres between two consecutive crests on the waves is called the wavelength. The amplitude of a wave is how far the wave displaces from its middle position (centre line) (see Figure 8.4).
transverse wave a wave in which the particles vibrate or move at right angles (perpendicular) to the direction of energy transfer crest the maximum displacement of a particle at the top of a wave trough the maximum displacement of a particle at the bottom of a wave displacement the position of a particle when it has moved away from its rest position on the centre line of a wave cycle one complete vibration or periodic movement of a particle through the crest and trough and back to its starting position; the length of a cycle is the wavelength period the time, in seconds (s), taken for a wave to complete one cycle frequency the number of cycles of a wave per second; measured in hertz (Hz) hertz a unit for measuring the number of cycles that happen every second (frequency); abbreviation Hz wavelength the distance from one wave crest to the next; measured in metres (m) amplitude the distance (height) of a wave crest or the depth of a wave trough from the centre line of the wave
Wavelength (one cycle)
Amplitude
Figure 8.4 Describing a transverse wave
Looking at wavelength and amplitude
Copy the diagram in Figure 8.5, using a ruler to make the sides of the grid squares exactly 1 cm long. On your copy, label the wavelength and amplitude of the waves. Use a ruler to measure these features.
Axis or centre line, the undisturbed or rest position of the particles
8.5 A depiction of a transverse wave
1. Explain what the word ‘transverse’ means in relation to waves.
2. Recall the three measurements that describe waves.
The vibrating strings in musical instruments, deep ocean waves and secondary seismic waves are examples of transverse mechanical waves.
Electromagnetic waves are another example of transverse waves. They consist of oscillating electric and magnetic fields, rather than disturbances in matter as a medium. Electromagnetic radiation is the transfer of energy by electromagnetic waves. The waves can transfer energy through a vacuum or through matter, such as when light from the Sun travels all the way to your skin through space, Earth’s atmosphere and a glass window.
An electromagnetic wave can be emitted from an atom when an electron jumps from one energy level to a lower one. This creates a changing electric field, which also creates a changing magnetic field. The two vibrating fields combine to create a self-propagating electromagnetic wave. An electromagnetic wave that carries a specific amount of energy related to its frequency or wavelength is called a photon of light.
The directions that the electric and magnetic field oscillate in are perpendicular to the direction of the wave, so an electromagnetic wave is a transverse wave.
Direction of wave travel
Figure 8.7 A vibrating charged particle generates vibrating electric and magnetic fields. These fields are perpendicular to each other and to the direction of the wave.
Unlike mechanical waves, electromagnetic waves all travel at the same speed through a vacuum –the speed of light, c = 3 × 108 m/s. The higher the frequency and the shorter the wavelength of an electromagnetic wave, the greater the energy carried by each photon. The relationship between frequency (f) and wavelength (λ) is described by the wave equation:
λ (m) = c (m/s) f (Hz)
The different types of electromagnetic waves, from lowest to highest energy, are illustrated in Figure 8.8. Their uses are described in the following list.
• Radio waves are useful for communications and signals over long distances (including radar). Radio waves were originally used for communication with ships at sea, then broadcasts by radio and television stations. They are now also used to send communications around the world via satellites. Radio waves have very long wavelengths (some are several kilometres long) but their energy and frequency are very low.
oscillating moving back and forth with periodic motion somewhat like vibration electromagnetic radiation the transfer of energy by electromagnetic waves self-propagating refers to a wave that (unlike mechanical waves) keeps going at a constant speed forever without needing the input of more energy photon an electromagnetic wave carrying a specific amount of energy related to its frequency or wavelength radio wave a type of electromagnetic radiation that has the longest wavelength microwave a type of electromagnetic radiation used for cooking, communications and Wi-Fi; lies between radio waves and infrared radiation
• Microwaves are used for cooking, Wi-Fi communications and mobile phone technology. In a microwave oven, any water molecules in food will vibrate at the same frequency as the microwaves and convert this energy into heat, cooking the food quickly. Much longer microwaves are used in mobile phone networks. When a mobile phone is switched on, it produces microwave signals (that you might know as 3G, 4G or 5G) that are picked up by receivers in mobile phone towers. The towers then transmit signals back to the phone for incoming calls, to connect to the internet and to download files, images and video.
infrared radiation
a type of electromagnetic radiation between microwaves and visible light; also known as heat radiation
visible light
the part of the electromagnetic spectrum that we can see
ultraviolet light a type of electromagnetic radiation between visible light and X-rays; needed by our bodies to make vitamin D; short-wavelength ultraviolet light can cause sunburn and cancer
X-ray a type of electromagnetic radiation that has short wavelengths and can pass through flesh to give images of bones; hazardous and can cause cancer
gamma ray a type of electromagnetic radiation that has high energy and a very short wavelength; produced when radioactive atoms decay
ionising radiation higher-frequency ultraviolet rays, X-rays and gamma rays, which can turn atoms and molecules into ions, which can damage living cells
• Infrared radiation is the radiation you feel immediately when you stand near a fire or when you feel warmed by the Sun. It is also used in home remote controls. Objects at a higher temperature release more infrared radiation than similar objects at a lower temperature. Infrared cameras can be used to detect infrared waves being emitted by an object. The signals are then processed to produce a false-colour image showing the relative temperatures of different parts of the object. Similarly, higher-frequency infrared waves can be detected by night-vision technologies to produce false green-coloured images.
• Visible light is the section of the electromagnetic spectrum that is visible to the human eye.
• Ultraviolet light is invisible radiation that can cause sunburn and skin cancer. Not all ultraviolet is bad: skin cells use low-frequency ultraviolet light to make vitamin D.
• X-rays are high-energy electromagnetic waves that are used to create images of bones. Bone absorbs most of the radiation whereas X-rays pass through soft tissue such as fat and muscle, so in X-ray images bones appear white, soft tissue appears grey and air appears black. The development of imaging technologies has contributed greatly to our understanding of the functions and interactions of body systems. X-rays damage human cells, although the radiation dose from medical scans is small.
• Gamma rays are high-energy, high-frequency waves with a short wavelength. They are released when atomic nuclei decay in nuclear weapons and nuclear reactors. Although this highenergy radiation can cause cancer, gamma rays can also be used in its treatment.
The higher the frequency and the shorter the wavelength of an electromagnetic wave, the more energy its photons carry. Higher-frequency ultraviolet rays, X-rays and gamma rays have enough energy to knock electrons off atoms, forming ions. This is referred to as ionising radiation, and it damages living cells.
infrared radiation to transmit signals to a TV.
remote must be pointed
because obstructions will block the infrared radiation from reaching the
We are all exposed to small amounts of ionising radiation in daily life. This is commonly referred to as background radiation. Its effect on the body is negligible because the exposure is so low. Under controlled conditions, the use of X-rays on living tissue is safe. In fact, the radiation dose from an X-ray is not much greater than that of background radiation. For example, a chest X-ray is equivalent to 2.4 days of exposure to natural background radiation, while a CT (computed tomography) scan, which also uses X-rays, of the abdomen is equivalent to 2.7 years of natural background radiation. X-ray imaging has different effects on different tissues.
Conduct some research to find out the different X-ray procedures and their associated natural background radiation equivalents, and discuss why they have different values.
• See: Observe the night sky as seen from Island Point in Perth, Western Australia in Figure 8.11.
• Think: Where does the light in the night sky come from? How long does it take for the light to reach your eyes from distant space?
• Wonder: What could the light from the night sky tell scientists about the age of the universe? What questions do you have after thinking about the lights in the night sky?
The See, think, wonder thinking routine was developed by Project Zero, a research centre at the Harvard Graduate School of Education.
Did you know that Wi-Fi was invented by an Australian? This physicist and engineer was actually studying radio waves being emitted from black holes and built a machine to detect these weak signals. This machine allowed computers to communicate wirelessly.
Conduct some research to answer the following questions.
1. Who is credited with inventing Wi-Fi?
2. When was Wi-Fi patented?
3. How does Wi-Fi work and what type of waves does it use?
4. What are some applications of Wi-Fi?
As wireless companies roll out their next-generation 5G networks around the world, people are excited for the faster download speed and reduced delays and, in some cases, worried about possible impacts.
In Western Australia, 4G networks work at frequencies between 700 megahertz and a few gigahertz. In contrast, 5G uses a few bands: those around 2–3 gigahertz and another at around 26 gigahertz. Waves with a frequency above 1 gigahertz are classified as microwaves; waves below 1 gigahertz are classified as radio waves.
Some people fear that 5G may behave like ionising radiation, which has been linked to cancer. Any wave that has a higher frequency than violet (visible) light can be considered ionising radiation. So, for 5G these fears are unfounded. The frequency of 5G is so low that it cannot ionise any atoms.
A more realistic concern, raised by meteorologists, is that 5G networks could disrupt weather forecasts from satellites because the frequencies used for 5G are extremely close to the frequency at which water molecules vibrate (23.8 gigahertz). Weather satellites use this frequency to track the water vapour in the atmosphere to give accurate weather forecasts. Because the frequencies are so close, 5G networks may interfere with weather satellites, reducing the reliability of the models that predict dangerous storms. For example, this could affect warnings for early evacuation of areas in the path of a storm.
wave summary
Table 8.1 summarises information about transverse waves.
Type of wave
How energy is transferred Is a medium required for propagation?
Mechanical wave As vibrations in particles between adjacent particles in a medium
Electromagnetic wave Carried as oscillating electric and magnetic fields
Table 8.1 The two types of transverse waves
Quick check 8.3
Yes
No
Examples
The strings in musical instruments, deep ocean waves, seismic waves
Radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, gamma rays
1. State which forms of radiation are most likely to be harmful to humans.
2. State two uses of radio waves.
3. State the wavelength range of microwaves.
4. Compare radio waves and microwaves.
5. State what property an object should have in order to emit a large amount of infrared radiation.
A longitudinal wave is a wave in which the particles of the medium oscillate (that is, vibrate) parallel to (in the same direction as) the energy transfer. The particles vibrate back and forth. As can be seen in Figure 8.13, longitudinal waves have areas where the particles (coils of a spring in this case) are close together and areas where they are spread apart. Places where the particles in a medium are closer together are called compressions, and places where the particles in the medium are further apart are called rarefactions. If a wave has more energy, then the particles in compressions are closer together and the particles in rarefactions are farther from each other.
Longitudinal wave in a spring Rarefaction Compression
The back-and-forth
Direction of wave
longitudinal wave a wave with vibrations in the direction of travel instead of transversely; e.g. sound waves
compression the part of a longitudinal wave where the particles are squashed together
rarefaction the part of a longitudinal wave where the particles are spread apart
Sound is a longitudinal wave because the air particles vibrate backwards and forwards in the same direction as the travelling sound wave. The motion of sound through the air is similar to when you move the end of a slinky forwards and backwards quickly to send a series of pulses through the spring (see Figure 8.14). When a sound wave passes through air, the movement of air particles is in a pattern that consists of regions of high pressure (compression) and regions of low pressure (rarefaction). Sound is a mechanical wave and therefore needs a medium to travel through, but the medium does not have to be air – it can also be a solid or a liquid. Sound travels faster through solids and liquids, where the particles are close together, than it does in air. It cannot travel at all through a vacuum (where there are no particles). Sound waves propagate through the air from the source of the sound to the listener. Sound waves can also reflect, or bounce back, off liquid and solid surfaces and send the sound wave propagating back in the opposite direction. Imagine shouting ‘cooee’ into a cave or a canyon – you might hear your shout again a few seconds later. This is because the sound waves that you have sent off into the air have reflected off surfaces and returned to your ears. This phenomenon is called an echo. Sound travels at about 343 m/s in air, so if the reflecting surface was at least 17 metres away, you would hear an echo 0.1 seconds later.
Direction of travel
Direction of travel
Explore! 8.3
echoes
Echoes are more useful than just hearing your own voice speak back to you!
Use the internet to find out how echoes are used in the following applications:
1. echolocation by dolphins
2. ultrasound in medicine
3. depth sounding in oceanography
4. seismic surveying in mineral and oil exploration.
8.15 Dolphins use echoes to help locate objects in the ocean.
Try this 8.2
Stretch out a slinky along the floor until it is a couple of metres in length. Create vibrations in the slinky by moving the coils back and forth. Observe the areas of compression and rarefaction that move back and forth along the length of the slinky.
Quick check 8.4
1. Define ‘sound’.
2. Define: a) compression b) rarefaction.
3. Explain why sound travels faster in solids than in air.
4. Explain how sound is an example of a longitudinal wave.
Aim
To hear and observe vibrations in the air.
Materials
• tuning fork
• rubber stopper
• 100 mL beaker containing water
• sounding board
Method
1. Strike the tuning fork on a soft surface, such as the rubber stopper.
2. Place the turning fork stem on the sounding board. Can you hear the sound clearly?
3. Repeat step 1 and lightly touch the vibrating ends of the tuning fork to the surface of the water.
4. Observe what happens to the water.
Results
Record your observations.
Discussion
1. Explain what you heard when you held the tuning fork to the sounding board. How does it work? Note that pianos also have a sounding board to make the sound of their vibrating strings louder.
2. Describe what happened when you touched the ends of the tuning fork to the surface of the water. Explain why this happened.
3. Could you identify areas of compression and rarefaction in the water?
In the same way that we can describe the properties of the transverse waves of the electromagnetic spectrum, we can also describe the properties of the longitudinal waves of sound. First, let’s recap the terms ‘wavelength’, ‘frequency’ and ‘amplitude’, this time with respect to sound waves.
• Wavelength (unit = metre) is the distance between two compressions or rarefactions of a wave (see Figure 8.17). The greater the distance between two points of maximum compression, the longer the wavelength.
• Frequency (unit = hertz) is the number of cycles (complete waves or vibrations) that pass a point each second. The more cycles or wavelengths that pass in a second, the higher the frequency.
• Amplitude (unit = metre) is the maximum displacement of air particles from their undisturbed position (see Figure 8.17).
This is the displacement amplitude. In a sound wave, which has regions of high and low pressure, the pressure amplitude is the difference between the maximum pressure in a compression and atmospheric pressure.
The pitch of a sound is how high or low on a music scale (not sound volume) it seems to our ears. The pitch of a sound wave is determined by its wavelength and therefore its frequency. Decreasing the wavelength increases how many wavelengths pass each second (frequency), and this increases the pitch of the sound. Lowpitched sounds have long wavelengths, whereas high-pitched sounds have short wavelengths (see Figure 8.18).
Figure 8.17 A sound wave represented as a graph of change in air pressure over distance or time. The air pressure change with no sound is 0, and + and – represent an increase or a decrease in pressure. The diagram above the graph shows the space between the air molecules and the regions of compression and rarefaction. Amplitude and wavelength now appear as they do for a transverse wave. Note that the graph is the same shape whether air pressure or the change in air pressure is plotted, or whether time or distance is the horizontal axis.
Short wavelength means many wavelengths per second; high frequency, high pitch
Long wavelength means fewer waves; low frequency, low pitch
Figure 8.18 Which of the two waves do you think would be a whistle and which would be a bass guitar?
The energy of a wave depends on its amplitude as well as its frequency. You might notice that not all water waves look the same: some waves are bigger than others. Amplitude is the maximum height of a wave from its resting position. If you were able to see sound waves, you would notice that loud sounds have a higher amplitude than soft sounds. When a drum is hit harder with more energy, it sounds louder – the loudness of the sound is a measure of the amount of sound energy. The unit of measurement for loudness of sound is the decibel (dB). The loudness of a normal conversation is usually about 60 dB. A rock concert is about 105 dB. Humans can hear sounds as low as 0 dB – this limit is called the threshold of hearing. Meanwhile, anything at around 85 dB can start to damage your hearing. Sounds louder than 120 dB can quickly cause irreversible damage.
8.19 The amplitude of a sound wave indicates the loudness of the sound. Amplitude
Quick check 8.5
1. Define the following terms and include the units.
a) Frequency
b) Wavelength
c) Amplitude
2. Consider the sound waves A–D, shown as pressure against time.
Identify which wave:
a) has the highest frequency
b) has the longest wavelength
c) you would expect to have the highest pitch
d) is the loudest.
WIDGET
determining the distance to a lightning strike
During a storm, it usually takes a few seconds for the sound to travel from the lightning flash to your ears. This is because light travels about 1 000 000 times faster than sound, which travels at about 343 m/s in air.
Figure 8.20 shows the relationship between the distance to the flash of lightning and the time delay before you hear the sound. Do you see any pattern in the graph?
Look carefully, and you will see that the line of the graph runs close to the points (3, 1000), (6, 2000) and (9, 3000).
This gives a simple rule for calculating the distance to a lightning strike: every 3 seconds is about 1000 m or 1 km.
8.20 A graph of the time between seeing lightning and hearing thunder versus distance to the lightning
active noise cancellation
Earphones with ‘active’ noise cancellation have a microphone that detects nearby sound waves and actively cancels them. This type of earphone technology can cancel sound waves up to about 75 dB, which provides users with a very immersive listening experience.
Conduct some research on how active noise cancellation works. Discuss the science with a partner.
Did you know? 8.2
All particles in the solid, liquid and gaseous states have a natural vibration that can be described by certain frequencies, called resonance frequency. When external sound waves, wind or other motion matches the natural frequency of particles in an object, the resonance frequency can amplify significantly.
This is how an opera singer is able to shatter a champagne glass with only their voice. The sound waves exerted by the singer travel at the resonant frequency of the glass particles, amplifying their natural vibrations so much that the glass shatters!
Acoustic instruments send sound waves into the body of the instrument such that sound waves resonate and amplify the projected sound.
Even bridges are designed with resonance in mind. If natural frequencies were able to influence the structural integrity of a bridge, it might resonate too much and collapse! Bridges are designed to minimise the impact of external frequencies.
Try this 8.3
sound insulation
Some students at a Western Australian school were comparing the published sound insulation data of some materials at school with data they obtained by experimenting in science class.
Sound insulation is the amplitude of sound waves (in dB) that are insulated or blocked from hearing before the average human would begin detecting the sound. Their results are as follows.
resonance frequency the natural frequency of vibrating particles in an object
1. Construct a column graph to present this data.
2. Describe any trends in the data.
3. Explain any observed trends in the data obtained by the students in comparison to published data.
Go online to
Surface waves travel along the interface between two different surfaces. For example, water waves travel along the interface between water and air. Surface waves are neither transverse nor longitudinal. In a surface wave, the individual particles move in a circle before returning to their original positions.
Making thinking visible 8.2
Connect, extend, challenge: the speed of light and sound waves
The speed of light and sound changes in different media, as shown in the table.
Approximate speed of wave (m/s)
Medium
1. What prior knowledge do you have that could help to describe the trends in the data?
2. Explain the trends in the table of data. Why is it that sound waves cannot travel in a vacuum?
3. Are there trends in the data that are difficult for you to explain? What are they?
The Connect, extend, challenge thinking routine was developed by Project Zero, a research centre at the Harvard Graduate School of Education.
Section 8.1 review
Online quiz
Section 8.1 questions
Remembering
1. State the types of electromagnetic radiation that are beyond the visible spectrum.
2. Identify the wavelength range of radio waves.
3. Recall the terms for the high-pressure and low-pressure areas of a sound wave.
4. Identify the correct words to complete the following sentences.
a) Pitch is determined by the ____________________ of a sound wave.
b) Loudness is determined by the ____________________ of a sound wave.
Understanding
5. The speed of light in air is 299 704 645 m/s. Calculate how long it would take for light to reach the following destinations from Perth. Hints: Convert the distances to metres. Divide each distance by the speed of light.
a) Adelaide (2134 km)
b) Brisbane (3607 km)
c) Sydney (3295 km)
d) Melbourne (2730 km)
6. You see a flash of lightning and 20 seconds later hear the thunder. Calculate how far away the storm is.
7. Explain how microwaves heat up food.
8. Explain what is meant by the term ‘longitudinal wave’.
9. Explain why sound cannot travel through the vacuum of space.
10. Explain why you see a flash of lightning before you hear the thunder.
Analysing
11. A wave has a frequency of 5 Hz and a wavelength of 70 m. Calculate the speed of this wave.
12. Compare microwaves and gamma rays.
Evaluating
13. Use the image shown here to determine why the loudness of a sound decreases as you move away from the source of the sound.
reflect change direction (of a wave) when hitting a surface boundary, so the wave continues to travel in the same medium
At the end of this section, I will be able to:
1. Explain how light is reflected from plane and curved mirrors.
2. Explain how light is refracted when passing through concave and convex lenses.
As described in the last section, light waves move perpendicular to oscillating electric and magnetic fields. This can be quite complex, and the direction of movement of light energy can be simplified using ray diagrams. Such diagrams show only the direction of the light ray, and these will be used in this chapter.
When light comes into contact with a surface, some or all of it may be reflected. If the surface is rough, the light rays bounce off the surface at different angles. The light is reflected but does not form an image.
light.
The light rays reflecting from a smooth surface bounce off at the same angle, and an image is seen.
Pepper’s Ghost is an application of light being reflected from a glass surface to make an actor appear as a ghost. It was commonly used in theatres in Victorian times as a special effect. If your school has a dark room, you might like to try and make your own Pepper’s Ghost.
Law of reflection of light
To understand the law of reflection of light, you first need to know some definitions.
• The incoming ray of light that hits the reflecting surface is called the incident ray.
• The outgoing ray of light that is reflected off the surface is called the reflected ray.
• The normal is an imaginary line that is at right angles to the surface.
• The angle between the incident ray and the normal is the angle of incidence (i).
• The angle between the reflected ray and the normal is the angle of reflection (r).
angle of incidence (i) = angle of reflection (r)
Quick check 8.6
1. State the law of reflection.
2. Explain what the law of reflection means.
The law of reflection of light states that the angle of incidence and the angle of reflection are equal to each other.
incident ray a ray of light arriving at a surface reflected ray a ray of light that is reflected off a surface normal an imaginary line that is at right angles to a surface angle of incidence the angle between an incident light ray and the normal, when the ray arrives at a surface angle of reflection the angle between a reflected light ray and the normal, when the ray leaves a surface
The reflection you see in a flat mirror, also known as a plane mirror, is called an image. The actual thing that is being reflected in the mirror is called the object. You will have seen your own reflection many times in glass mirrors and windows, polished metal and even the surface of still water. You have probably noticed that the image formed in a mirror is upright but is inverted from left to right (called a lateral inversion), so if you raise your right hand in front of a mirror you will see your image raise its left hand.
When you look at an object in a plane mirror, the image appears to be behind the mirror. This is known as a virtual image. The image appears to be the same distance behind the mirror as the object is in front of it. What other characteristics of this virtual image do you notice? Is it the same size as the real object?
A concave mirror curves inwards, like a cave. Concave mirrors can be used to magnify images and are commonly used for shaving or applying make-up.
Figure 8.30 If you hold a concave mirror close, it will magnify your image (a virtual image), as shown here. But if you moved a long distance away from the mirror, it would turn your image upside down (a real image).
When parallel rays are reflected from a concave mirror, they converge at a focal point. The focal point is where an image forms. In Figure 8.31, the image is in front of the mirror, and is known as a real image
Concave mirror
Focal point (image)
concave for a lens, having an outline that is thinner in the middle; for a mirror, curved inwards, like a cave
Figure 8.31 When an object is far from a concave mirror, the reflected light rays converge to form a real image. If the object was close to the mirror, it would form a large virtual image, as in the shaving mirror shown in Figure 8.30.
convex for a lens, having an outline that is thicker in the middle; for a mirror, bulging outwards
Convex mirror
Convex mirrors bulge outwards and give a wider field of view. They are used in car rear view mirrors to allow drivers greater visibility. You may also see large convex mirrors at intersections that have limited visibility, or in the hallways of hospitals to provide a view of what is around the corner.
Figure 8.32 A car’s side view mirror is often a convex mirror. It gives a wider field of view, but also makes objects appear smaller and closer than they actually are.
When light rays are reflected from a convex mirror, they diverge. An image forms behind the mirror –this is a virtual image.
Convex mirror
Focal point (image)
Figure 8.33 Reflected light rays diverge from a convex mirror. The image formed is a virtual image.
Did you know? 8.4
images
A real image is an image that can be projected onto a screen, like a film projected onto a cinema screen. In a ray diagram, a real image forms where the light rays actually do converge. A real image is always upside down, like the image that forms on the retina of your eye.
1. Describe the image formed in a plane mirror.
2. Describe three differences between images formed in convex mirrors and those formed in concave mirrors.
Practical 8.2
Investigating ray diagrams with concave and convex mirrors
Aim
To observe and record the way in which light rays are reflected from curved mirrors
Materials
• light box
• clear ruler
• pencil
• concave mirror
• convex mirror
• white A4 paper
Method
Be careful
The light box can become hot with prolonged use.
1. Plug in the light box and position it at the edge of a piece of A4 white paper.
2. Place the triple ray-forming plate into the slot and turn on the light box. Adjust the position of the bulb until you see three parallel rays of light on the paper.
3. Place the concave mirror about 10 cm in front of the rays, and align it so that the middle ray reflects back on itself.
4. Use a pencil to outline the mirror, and use a clear plastic ruler to trace the incident and reflected rays.
5. Label the point at which they meet the ‘focal point’.
6. Get a new piece of paper and repeat steps 3 and 4 with a convex mirror.
7. Trace the reflected rays back behind the outline of the mirror with dotted lines.
8. Label the point at which the dotted lines meet the ‘virtual focal point’.
Results
On your ray tracing diagrams, measure how far the focal point or virtual focal point is from the mirrors. Include this in your diagrams.
Discussion
1. Do the focal lengths for the convex and concave mirrors differ?
2. Why does the convex mirror produce a ‘virtual focal point’?
Conclusion
1. Make a claim regarding light rays reflected from curved mirrors. Start your sentence with: ‘This experiment suggests that with curved mirrors … ’.
2. Support your claim by using what you observed when you used convex and concave mirrors. Start your sentence with: ‘It was observed that … ’.
3. Explain how the data supports your claim. Start your sentence with: ‘This means that … ’.
refraction the bending of light as it passes from one medium to another
When light travels from one substance into a different substance at an angle, it bends. This bending of light is called refraction. Refraction happens because light may slow down or speed up when it enters a different substance. Imagine a line of people running on a hard surface. When one end of the line encounters sand, it has to slow down. The runners in the sand will move slowly, while the rest of the runners continue to run fast. Eventually all the runners will enter the sand, but by now the direction of the runners has changed. The same thing happens when light travels from air into water.
refractive index
a measure of how much the speed of light changes as it passes from a vacuum into a particular substance
Figure 8.34 The direction the light is travelling in (shown by red arrows) changes when it moves from air (fast) into water (slow).
Each material has a refractive index, which is a measure of the change in the speed of light as it moves from a vacuum into that material (see Table 8.2). Light travels fastest in a vacuum, and it slows down if it enters materials such as air, glass or water. It only slows down a little bit in air. In water, the speed decreases by a factor of 1.33, and in glass it decreases by a factor of 1.52.
Table 8.2 The speed of light in different materials, and their refractive indexes
Figure 8.35 The pencil appears bent, due to the refraction of light at the surface of the water.
Try this 8.4
Place a 20 cent coin in the bottom of a cup and move back just until you can’t see it. Then add water without moving your head. As you do so, the coin will appear.
When travelling through a hot desert, people often think they can see water or trees on the ground ahead of them. In reality, there is nothing there. It is a trick of the light, called a mirage. Light rays coming from distant objects are refracted by cold and warm air. This tricks our eyes into thinking that the light rays are coming from objects on the ground instead of the sky.
Light bends in a certain direction as it enters and leaves different materials. When light travels from a material with a lower refractive index into a material with a higher index (for example, from air into water), it slows down and bends towards the normal (see Figure 8.36a).
Conversely, when light travels from a material with a higher refractive index into a material with a lower refractive index (for example, from water into air), it speeds up and bends away from the normal (see Figure 8.36b).
bends away from the normal
Figure 8.36 The direction light bends is dependent on the refractive index of the materials it enters and leaves. Water has a higher refractive index than air, so (a) when light enters water it bends towards the normal, and (b) when light leaves water it bends away from the normal.
1. Define the term ‘refraction’.
2. Explain how refraction differs from reflection.
3. Describe the difference between a material with a refractive index of 1.32 and one with an index of 1.74.
4. State whether light will bend towards or away from the normal when it is travelling from a material with a refractive index of 1.02 into a material with a refractive index of 1.4.
Prisms
Light bends when it enters a rectangular block, and bends back to its original direction when it leaves the block.
Figure 8.37 Light passing through a sheet of glass or a rectangular block emerges in the same direction as when it entered.
A triangular glass prism has a triangular face, usually an equilateral triangle, which is the same throughout its length. prism a piece of glass with a triangular cross-section that can be used to separate white light into its colours
8.38 A prism
To use a prism, light is shone at an angle through the side of the prism. The light that emerges from the other side has been bent twice – when going into the prism and when coming out.
Figure 8.39 As light enters a prism, it slows and bends (A). It travels through the prism and bends a second time when it speeds up as it leaves (B).
Different colours bend through different angles. Therefore, when white light passes through a prism, the different colours separate out from each other. Isaac Newton discovered that white light is a mixture of colours, which he called the spectrum. Newton was the first person to use a prism to separate the colours. He also discovered that once a colour (say, red) is separated out from white, it cannot be separated any further. It stays the same (e.g. red stays red) in all further experiments. He concluded from this that white light is a mixture of the different colours of the spectrum.
8.40 A beam of white light is refracted by a prism to form a spectrum. There are some reflected rays, and these remain white. Only the refracted rays form a spectrum.
Try this 8.5
Making a rainbow
You will need:
• a light box
• a prism
• a piece of white card.
Set up the light box in a dark room with a single-ray forming plate, so that a thin beam of white light is shining from one end. Place the prism so that the light enters one of the rectangular faces at an angle. Play around with the angle of the beam of light until you get a rainbow.
1. Explain how a prism separates white light into its different colours.
2. Describe how light bends when it enters and leaves a rectangular block.
Aim
To investigate refraction of light through a glass block
Materials
• glass rectangular block
• light box
• sheet of A4 white paper
• protractor
• clear plastic ruler
• pencil
Method
Be careful The light box can become hot with prolonged use.
1. Connect the light box to a power source and insert a single-ray forming plate.
2. Place the light box on the piece of white paper and switch it on.
3. Direct the single ray towards the glass block, as shown in in Figure 8.41.
4. Trace the outline of the glass block onto the white paper. Use the clear ruler to trace the path of the incident ray and the refracted ray.
5. Remove the glass block and connect the two lines to visualise the path of the light through the glass.
6. Use the protractor to make measurements of the angles, and record your results in the results table.
Results
Light box i
Glass block
Figure 8.41 Experimental set-up
Table showing angle of incidence and refraction of light entering and leaving a glass block
Angle of incidenceAngle of refraction
Light entering glass
Light leaving glass
Discussion
1. Does light bend towards or away from the normal when: a) entering glass b) leaving glass?
2. What do you notice about the beam of light that is entering the glass and the beam of light that is leaving the glass?
3. Does all the light travel through the glass and emerge from the other side?
Conclusion
1. Make a claim regarding light refraction through materials. Start your sentence with: ‘This experiment suggests that light … ’.
2. Support your claim by using what you observed. Start your sentence with: ‘It was observed that … ’ and include potential measurement uncertainties and experimental faults.
3. Explain how the data supports your claim. Start your sentence with: ‘This means that … ’. Practical 8.3
There are two types of lenses: convex and concave.
Convex lenses are thick in the middle and thin at the edges. An example of a convex lens that you are probably familiar with is a magnifying glass. If you look carefully at a magnifying glass, you will see that it is fatter in the middle and thinner at the edges. The magnifying glass makes the image appear bigger than the original object. Figure 8.43 shows how this happens.
However, when the distance between the convex lens and the object increases, the image can be upside down and sometimes smaller. This type of image is a real image.
Figure 8.42 A magnifying glass creates an image that is larger than the actual object.
Figure 8.43 How a magnifying glass works. A convex lens makes the light rays converge, or bend inwards from their original path. The black lines represent the actual path of the light, the red dashed lines show where the light appears to come from. The image is upright, virtual and magnified.
Concave lenses are thin in the middle and thick around the edges. A concave lens has the opposite effect to a magnifying glass – it makes a smaller image. Rays that pass through a concave lens bend in the opposite direction to those passing through a convex lens (see Figure 8.44).
Concave lens
Figure 8.44 A concave lens makes the light rays diverge, or bend outwards from their original path. The black lines represent the actual path of the light, the red dashed lines show where the light appears to come from. The image is upright, virtual and smaller than the real object.
Aim
To investigate the refraction of light through different lenses
Materials
• light box
• A4 white paper
• clear ruler
• pencil
• biconvex lens
• biconcave lens
Method
Be careful
The light box can become hot with prolonged use.
1. Connect the light box to a power source and place it on the white paper.
2. Insert a triple-ray forming plate into the light box so that three parallel light rays fall onto the paper.
3. Place the biconvex lens onto the paper and trace its outline. Use the clear ruler to trace the three incident rays and the three refracted rays.
4. Repeat step 3 on a new piece of paper, but replace the biconvex lens with a biconcave lens.
Results
1. Label all your diagrams and give each page a title.
2. Measure and record the distance from the centre of each lens to the focal point.
Discussion
1. Describe the difference in the refraction of light between biconcave and biconvex lenses.
2. Which lens produces a real focal point and which lens produces a virtual focal point?
3. Do all the incident rays refract? If not, which ones do not?
Conclusion
1. Make a claim regarding refraction through curved lenses. Start your sentence with: ‘This experiment suggests that curved lenses … ’.
2. Support your claim by using what you observed. Start your sentence with: ‘It was observed that … ’.
3. Explain how the data supports your claim. Start your sentence with: ‘This means that … ’.
1 Describe the difference between a convex lens and a concave lens.
2 Identify the type of lens used to magnify images.
3 Identify the type of lens that makes light rays diverge.
total internal reflection
As you know, when light travels from one medium to another, it is refracted either towards or away from the normal. If the light bends away from the normal, the angle of refraction can be up to 90°. Here the angle of incidence is called the 'critical angle'. If the angle of incidence is greater than the critical angle, light cannot escape at the boundary. It is instead reflected back into the first medium. This is known as total internal reflection. Fibre optic cables use total internal reflection to confine light to the cable in order to transmit information with minimal signal loss.
Do some research to find answers to the following questions.
1. What does total internal reflection have to do with diamonds?
2. What other examples of total internal reflection can you find?
Did you know? 8.6
Researchers have found that the Saharan silver ant uses total internal reflection to survive in extremely hot environments. Silver in colour, these ants have body hairs that totally internally reflect light, allowing them to forage in deserts where the temperature is over 50°C. Each hair has a triangular cross-section, like a long prism, and reflects most of the light (and heat) that hits it. This reflection of light and heat helps keep the ant cool and gives it a silvery sheen.
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Section 8.2 review
Online quiz
Section 8.2 questions
Remembering
Section questions
Teachers can assign tasks and track results
1. State the law of reflection of light.
2. Define the term ‘refraction’.
3. Describe what a concave lens and a convex lens do to an image.
Understanding
4. Explain why some objects are reflective and create an image, and others are not reflective.
5. Copy the diagram in Figure 8.48 into your book and label it with the following terms:
Incident ray
Reflected ray
Angle of incidence
Angle of reflection.
6. Explain how the reflection of an object in a mirror differs from the actual object in real life.
7. Explain the difference in uses for concave and convex mirrors.
8. Describe what happens to light rays as they pass through a convex lens versus a concave lens.
Applying
9. Explain why the woman in the swimming pool in Figure 8.49 looks distorted.
10. Identify whether a convex or concave mirror would be useful in the following situations.
a) A security mirror in a hospital
b) A mirror at an intersection to allow greater visibility
c) A mirror to help a person apply eye makeup
Analysing
11. Suggest what sort of object might be used in a reflecting telescope, as opposed to a refractive telescope. Justify your response.
Evaluating
12. Suggest how the reflections of the people in Figure 8.50 are being distorted.
cornea the transparent outer covering of the eye
pupil the circular black area in the centre of the eye through which light enters iris the coloured circular part of the eye that surrounds the pupil
vitreous humour
the clear jelly-like substance in the eyeball through which light passes choroid
a layer of blood vessels in the eye that supply the retina
ciliary muscle a muscle in the eye that controls the focus of the lens by changing its shape
sclera
the white outer layer of the eyeball
lens (eye)
a small disc of transparent tissue behind the pupil that allows the eye to focus on near and far objects
fovea
a small part of the retina that contains the most lightsensitive cells
retina an area of tissue at the back of the eye that contains cells that detect light and colour
At the end of this section, I will be able to:
optic nerve the nerve that connects the eye with the brain
1. Label diagrams of the human eye and ear.
2. Discuss the use of corrective technology in vision and hearing loss.
You already know that eyes are amazing, and ever since you were little you have probably been told to protect your eyes. This is because you only have one set of eyes and they may not repair themselves if they suffer certain types of damage.
The structure of the human eye is illustrated in Figure 8.51. Light enters the human eye through the cornea and then through the small hole at the front called the pupil. The size of the pupil is controlled by the iris muscles, which form the coloured part of the eye.
humour
Lens
Cornea Pupil Iris
Ciliary muscle
Retina Fovea
Optic nerve
If you are somewhere dark, the pupil’s size will increase to let in as much light as possible. On a bright sunny day, the pupil’s size will reduce to limit the amount of light that enters, in order to protect the eye. Just behind the iris is the lens, which focuses the light on to the fovea, a small area on the retina at the back of the eye. The retina is covered in a thin layer of specialised light-receptor cells that send impulses to the brain about the light they receive via the optic nerve
The image we see on the retina is upside down (see Figure 8.52). Our brain turns the image the correct way up.
When you change what you are looking at, the lens of your eye automatically adjusts to become more curved for near objects and less curved for distant objects. The ciliary muscles adjust the focus of the lens and are controlled by the autonomous nervous system, which handles unconscious tasks. This means you do not have to think about focusing when you lift your eyes from a book to look at a distant tree. This process of adjustment is called accommodation
Not all eyes are the same. Some organisms’ eyes are very different to human eyes. In fact, most animals see very differently to one another; their eye structure varies according to the type of animal and how they live. A bee sees the world very differently to how we see it! Use a search engine of your choice to explore the following questions.
1. How does an earthworm see?
2. How are a scallop’s eyes different to those of almost every other animal on the planet?
3. How does the position of the eyes on the face differ between animals? How does this change their view of the world?
Anablepinae anableps, or the four-eyed fish, has four eyes: two to see above the water and two to see below!
accommodation automatic adjustments made by the eye when looking at objects at different distances
Practical 8.5
Most of us have a dominant hand, that is, the hand we prefer to use for more precise performance. Just like a dominant hand, most of us have a dominant eye. This is the eye that our brain prefers when processing visual input. Visual information is still gathered through both eyes, but more precise visual information comes from the dominant eye. This is the eye that we should use in activities that involve aiming.
Aim
To determine whether eye dominance is related to hand dominance.
Planning
Is an individual’s eye dominance always the same as their hand dominance? Propose a hypothesis.
Materials
An object on a wall or far away that can be the subject of focus.
Method
1. Draw the results table below.
2. Use your dominant hand to create a ‘monocle’ with your fingers as shown.
3. Find an object in the distance, such as a clock. With both eyes open, try to view it through the hole.
4. Once you can clearly view the object through the hole, close your left eye so you are only looking at it with your right eye. If you can see the object through your hand, then you are right-eye dominant. If you cannot see it, then close your right eye so you are only looking with your left eye. You should now be able to see it through your hand and it means you are left-eye dominant.
5. Survey your entire class. Of those who are right-eye dominant, how many are righthanded? How many are left-handed? Of those who are left-eye dominant, how many are left-handed? How many are right-handed? Fill out the results table.
Results
Table showing proportions of hand and eye dominance in the class
Right-eye dominant
Left-eye dominantTotal
Right-hand dominant
Left-hand dominant
Total
Discussion
1. Calculate the percentage of the class who are right-hand dominant. What percentage are left-hand dominant? Identify whether the proportions are even.
2. Calculate the percentage of the class who are right-eye dominant. What percentage are left-eye dominant? Identify whether the proportions are even.
3. Determine whether all right-hand dominant individuals are right-eye dominant as well. Do the same for left-eye dominance.
4. Does your data support your hypothesis?
Conclusion
1. Draw a conclusion from this experiment on eye dominance, supporting your statement with data.
Quick check 8.11
1. Draw a flow chart to summarise the path of light from outside the eye to the retina.
2. Identify the missing information in the table below.
Part of the eye
To focus light onto the retina
different-shaped windows for seeing Researchers have found that an animal’s ecological niche (the role that an organism plays in an ecosystem) determines the shape of its pupil. Remember, the pupil is the hole through which light is let into the eye. In humans, the pupil is round. Some animals, such as cats, have slits for pupils. This is typical of animals that are active in both the daytime and the night-time. Grazing animals, such as sheep, have horizontally elongated pupils in order to easily survey the landscape for predators.
long-sighted able to see distant things clearly, but not things that are close short-sighted able to see close things clearly, but not things that are far away
Sometimes the eye needs a bit of help. For example, the lens in a person’s eye may be unable to curve sufficiently or the eyeball may be abnormally short. In both these cases, this causes the image to be formed behind the retina, allowing the person to see distant objects clearly but making near objects blurry. We call this condition long-sightedness, and it can be corrected with a convex lens that converges the light waves entering the eye. Because the activity most associated with close-up vision is reading, the glasses used to treat long-sightedness are often called reading glasses. Reading glasses are essentially a support for the lens, helping by refracting the light before it reaches the eye, providing more overall bending.
People who are short-sighted have an eyeball that is abnormally long, or a lens that is too thick. This means the image is formed in front of the retina, giving the ability to see near objects clearly, but distant objects are blurred. Concave lenses can be used to cancel some of the effect of the curved lens in the eye by diverging the light waves entering the eye, allowing the person to see distant objects clearly.
Long-sightedThe lens in the eye is not curved enough
Short-sightedThe lens in the eye is too curved
Convex lenses worn as glasses to provide extra bending of light
Concave lenses worn as glasses to cancel some of the curvature
Table 8.3 Causes and solutions for long-sightedness and short-sightedness
Figure 8.55 The diagram shows how the light is not focused correctly in short-sighted and long-sighted eyes, but this problem can be overcome by wearing corrective lenses.
Explore! 8.8
astigmatism and cataracts
Many eye defects require treatment or correction of the eye’s lens.
Use the internet to identify the causes of the following eye defects and how they are corrected.
1. Astigmatism
2. Cataracts
Science inquiry 8.2
The Monash Vision Group at Monash University in Melbourne has been developing the Gennaris bionic vision system, also called the ‘bionic eye’. Functioning eyes detect visible light waves, and then nerve impulses are sent from the optic nerve to the brain to construct an image. For many people who are blind, the optic nerves are not working and so nerve impulses are not sent to the brain when the eyes detect visible light waves.
The bionic eye consists of wearable glasses and a headset. The glasses contain a camera that detects visible light waves. The headset contains a vision processing unit, which wirelessly interacts with an implanted tile in the user’s head. The implanted tile then sends nerve impulses to the brain in the same way that a functioning optical nerve would. It is predicted that users will gain enough sensory information to be aware of their surroundings in both indoor and outdoor environments.
ear canal
a tube that connects the outer ear and the middle ear
eardrum a thin piece of membrane inside the ear that moves backwards and forwards very quickly (vibrates) when sound waves reach it
cochlea
a spiral tube inside the inner ear that produces nerve impulses in response to sound waves; the main organ of hearing auditory nerve the nerve that connects the ear with the brain
Quick check 8.12
1. Explain the terms ‘long-sightedness’ and ‘short-sightedness’.
2. Explain how reading glasses help long-sighted people.
Like the eye, the ear is amazing! How does it turn vibrating air particles into messages our brain understands as sound? Let’s have a look at the structure of the ear.
In order for us to hear a sound, the energy from the sound needs to be transmitted from our outer ear to our inner ear. It must pass through a number of structures before it gets there. The outer ear has the job of funnelling sound waves from the environment into the ear. The sound waves travel through the ear canal and arrive at the eardrum in the middle ear. As you know, sound waves are the vibration of particles – these vibrations cause the eardrum to vibrate. The vibrations are passed on to three tiny bones called the hammer, anvil and stirrup – also known as the malleus, incus and stapes, respectively. The eardrum causes these three bones to vibrate, and in turn this causes the vibration of fluids in the cochlea. This part of the ear is the inner ear.
Finally, in the cochlea, the vibrations are converted into electrical impulses, which travel along the auditory nerve to the brain (as part of the nervous system), where they are interpreted as sound.
Some people who experience mild hearing loss wear a hearing aid. Hearing aids make sounds louder so the person can participate in everyday life more effectively. However, some people have severely impaired hearing and cannot hear any sounds at all. This kind of impairment can sometimes be managed with a cochlear implant.
Science inquiry 8.3
The cochlear implant was pioneered in Australia by Professor Graeme Clark. Unlike a hearing aid, which is worn outside the ear, a cochlear implant is surgically placed inside the ear. It consists of a microphone worn outside the ear to detect sounds and a processor that can be worn in a pocket that converts the sound into electrical signals. These signals are sent to the implant in the cochlea, which stimulates the auditory nerve and allows the patient to hear.
Quick check 8.13
1. Identify the missing information in the table below.
Part of the ear
Eardrum
Ear canal
Function
Contains fluid and specialised cells that detect vibrations from the middle ear and converts these to electrical signals
Collects electrical signals from the cochlea and sends them to the brain for interpretation
2. Recall the threshold of human hearing.
Excessive noise can damage the delicate hearing cells in the inner ear. People who work with noisy machinery can be exposed to sounds above 85 dB, which can damage their hearing with prolonged exposure. If the delicate cells that detect sound in the inner ear are damaged, they cannot be replaced. This can cause hearing loss, or a disorder called tinnitus, in which a person hears a permanent ringing noise in their ears. To prevent this from occurring, people who are constantly exposed to loud sounds wear ear defenders to protect their hearing.
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Explore! 8.9
Deafness occurs because the auditory nerve cannot effectively transfer the information provided by sound waves entering the outer ear. Do some internet research to find answers to the following questions.
1. What is conductive deafness and what could cause it?
2. What is sensorineural (nerve) deafness and what could cause it?
3. Would the use of grommets help to improve conductive or sensorineural (nerve) deafness?
4. Would the use of a cochlear implant help to improve conductive or sensorineural (nerve) deafness?
Quick check 8.14
1. Recall one reason why someone can lose their hearing.
2. Contrast a hearing aid and a cochlear implant.
Section 8.3 review
Online quiz
Section questions
Teachers can assign tasks and track results
Section 8.3 questions
Remembering
1. State which structure in the eye focuses light.
2. Name the type (shape) of lens that is in the human eye.
3. Recall the parts of the ear that make up the middle ear.
4. Define the term ‘accommodation’.
5. Recall the purpose of the ear canal.
6. Recall which type of corrective lens a person with long-sightedness should wear.
7. State what will happen to your pupil in the following situations.
a) Standing outside on a sunny day
b) Walking into a dark room
Understanding
8. Explain how the iris and the pupil work together.
9. Explain which parts of the eye deteriorate over time, causing long-sightedness.
10. Draw a diagram to illustrate how light enters the eye and is focused on the retina.
Applying
11. Explain how the shape of the lens changes if an object is: a) up close b) far away.
12. Describe the shape of the pupil of animals that need to watch the landscape for predators.
13. ‘Retinal detachment’ occurs when the retina becomes separated from the back of the eye. It is a medical emergency. Apply your knowledge of the retina to explain why it is an emergency. Use the Figure 8.62, which shows a human eye in side-on view, to help you.
Choroid
Analysing
14. Compare the kinds of corrective technology needed for long-sightedness versus shortsightedness. Provide reasons for the difference.
Evaluating
15. Decide why people need to visit their optometrist every 1–2 years to get their eyes checked.
16. Discuss what may happen to a person’s ability to hear if their eardrum has burst.
17. Propose what might happen to a person’s hearing if they had to get their outer ear removed.
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Chapter checklist
Success criteria Linked question
8.1I can distinguish between mechanical and electromagnetic waves.3
8.1I can identify the different parts of a wave, including the wavelength, amplitude, trough and crest. 5
8.1I can recall the different parts of the electromagnetic spectrum.15
8.1I can describe compression and rarefaction in longitudinal waves.6
8.2I can explain how light is reflected from plane and curved mirrors.14
8.2I can explain how light is refracted when passing through concave and convex lenses. 10
8.3I can describe the structure and function of the eye. 8
8.3I can describe the structure and function of the ear. 21
Scorcher competition
Review questions
Data questions
Review questions
Remembering
1. State the unit of frequency of waves, and describe what it measures.
2. Identify the correct words related to the direction of wave travel to complete the following sentence.
Sound waves are ______________ waves, whereas electromagnetic radiation is made up of ______________ waves.
3. State which types of electromagnetic radiation have a higher frequency than visible light.
4. Define the following terms: wavelength, frequency, amplitude, pitch.
Understanding
5. Describe the difference between compression and rarefaction.
6. Explain what is necessary for a sound wave to travel from one place to another.
7. Explain why the image formed on our retina is upside down, and suggest why we do not see the world upside down.
8. Explain how wearing glasses can help correct sight problems such as long- and shortsightedness.
9. Explain why a concave lens creates a reduced image, and why this is called a ‘virtual’ image.
10. Using your knowledge of infrared radiation, explain how night vision goggles work.
11. Two astronauts are completing a space walk outside the International Space Station. a) Explain why radios are necessary for communication between the two astronauts. b) Imagine that the radios were broken. Describe some other ways the astronauts could communicate.
Applying
12. Identify whether altering the frequency or the amplitude would be required in the following situations.
a) Singing a higher-pitched note
b) Going from a high note to a low note on the guitar
c) Changing from talking to whispering
13. If you wrote the word SCIENCE on a piece of paper and held it up to a plane mirror, draw what the reflection in the mirror would look like.
14. Identify some examples of objects that are similar in size to the wavelengths of the following types of radiation. One has been completed for you.
Type of radiation
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Wavelength Object
1 metre to a few kilometresBuildings
1 millimetre (mm) to 1 m
0.7 micrometres (μm) to 1 mm
400 nanometres (nm) to 700 nm
10 nm to 400 nm
10 picometres (pm) to 10 nm
Gamma rays shorter than 10 pm
Analysing
15. Figure 8.63 depicts four people participating in a Mexican wave. Analyse the figure to work out whether a Mexican wave is an example of a transverse wave or a longitudinal wave. Justify your response.
16. Compare the particle model and the wave model in terms of energy transfer and how they travel through matter.
17. Contrast the transfer of light and sound energy. You may choose to do so in a table as shown.
Medium
Particle or wave model
Type of wave
Direction of energy transfer
Evaluating
18. A person standing 1 km away shoots a gun. You see the flash of light to indicate that the gun has been fired but you do not hear anything immediately.
a) State why this is the case.
b) If it takes 3 seconds after you see the gun fired to hear the gunshot, calculate the speed of the sound.
c) Discuss how close this value is to the actual speed of sound in air.
d) Propose some reasons why it may be different.
19. The table shows the average smallest distance at which a person can see a clear image, at different ages. Use the table to answer the questions that follow.
a) Suggest some reasons why sight changes with age.
b) Propose whether an older person is more likely to need convex or concave lenses to correct an eyesight problem. Justify your proposition.
20. Suggest some occupations that could give workers excessive exposure to loud noises. Then propose some policies that could be put in place to prevent permanent hearing loss.
A 20 year old took their 80-year-old grandparent for a hearing loss evaluation and decided to take the auditory test as well. An audiogram shows the lowest volume at which a person can hear a sound at a particular frequency. (Note that the values on the vertical axis are in decreasing order.)
The audiogram results for the 20 year old and the 80 year old are illustrated in Figure 8.64. Hearing is considered normal if you can hear sound volumes over 30 dB at a particular frequency. Hearing loss is considered moderate if you require volumes of 30–60 dB, and severe if you can only hear sound volumes over 60 dB.
Figure 8.64 An audiogram for a 20 year old and an 80 year old
1. Identify which person required a sound to be louder in order to hear it at a sound wave frequency of 2000 Hz.
2. Determine the lowest volume of the 1000 Hz sound wave that can be heard by the 20 year old, based on the test.
3. Recognise which person displays hearing loss.
4. Identify a trend in volume and frequency for both the 20 year old and the 80 year old.
5. Analyse the plot for the 80 year old and find any frequencies where the person experiences severe hearing loss.
6. Contrast the two data sets between the frequencies of 1000 Hz and 2000 Hz.
7. Following the trend in the data, deduce the lowest volume at which the 20 year old can hear a frequency of 9000 Hz.
8. Predict whether the 80 year old would more easily hear a person talking or a higherpitched bird whistle at the same volume.
9. The outcome of the test was that the 80 year old is living with ‘moderate low-pitch hearing loss and severe high-pitch hearing loss’. Justify whether this statement is accurate.
Music is part of most of our lives – whether you listen to music, play an instrument or even create your own music. Music can be defined as sounds that are organised in time and vary in pitch (the frequency of the sound), dynamics (loudness and softness) and timbre (the tone of the sound).
All musical instruments have three main components:
• a primary vibrator that produces the sound (for example, a violin string when you draw a bow across it, or a flute mouthpiece when you blow across it)
• a primary resonator that amplifies the sound (for example, the space inside a violin or a flute)
• an opening for the sound to effuse (flow out) from (for example, the f-holes of a violin or the open end of a flute).
Pitch is varied in different ways depending on the type of instrument. In a wind instrument, the pitch is varied by changing the length of the tube (usually by opening and closing holes). In a stringed instrument, the pitch can be varied by changing the tension in the string, the length of the string or the mass (thickness) of the string.
Design and build an accessible musical instrument from recycled materials.
Musical instruments have been developed by every human culture in history – making music is a universal human trait. Studies have shown that listening to music can reduce anxiety, depression and even pain, and it can improve memory, mood and even sleep. Learning to play an instrument has positive effects on the brain, which translate to other areas of learning. Because music strengthens neural pathways, it can also help to delay ageing of the brain. Historically, people with some types of disabilities have been limited in the ways they can engage with music, because of the fine motor skills usually associated with learning to play an instrument. Engineers have been able to modify existing instruments or design new ones to help people with disabilities engage with music.
In small groups your task is to design and build a musical instrument that is accessible to people with a disability or elderly people. The first step will be to decide what type of condition you would like to cater for. You may need to do some research into the condition to help understand the potential problems that elderly people or people with a particular disability may encounter in using traditional instruments.
• plastic containers
• elastic bands
• bottles
• icy-pole sticks
• scissors
• cardboard
1. Discuss in your group which condition you will cater for, and research how this condition affects the ability to play a musical instrument.
2. Discuss in your group which type of instrument you will focus on – will you build a woodwind, string or percussion instrument? (It might be difficult to find the resources to build a brass instrument.)
3. Research all the components required for the instrument you are going to build, and list all the ways you can change the pitch and/or volume of sound.
4. As a group, make multiple sketches each and work out which design would be most effective.
5. Design your prototype and focus on how it can be made from sustainable materials.
6. Build your prototype and test the quality of the sound produced by your instrument.
7. Discuss the challenges you experienced when designing and building your musical instrument, and list the methods you used to overcome these.
8. Describe the method by which your instrument produces sound and changes pitch.
9. Evaluate how easy or difficult it is to use or learn your instrument.
10. Suggest some improvements to your instrument that could make it easier to use.
accuracy how closely a measurement matches the ‘true’ or accepted value
calibration adjusting measuring equipment against a known standard value to ensure its accuracy confounding variable an external factor that can unintentionally affect the outcome of an experiment, making it difficult to determine whether changes in the dependent variable are caused by the independent variable
continuous data quantitative (numerical) data points that have a value within a range; usually measured against a scale that includes decimals or fractions (e.g. length in metres)
controlled variable a factor that remains constant throughout an experiment, to ensure that any changes observed in the dependent variable are solely due to the manipulation of the independent variable correlation the relationship between two variables cultural appropriation the use of cultural knowledge or tradition without acknowledgement or consent dependent variable the variable that is measured during an experiment (as it responds to the independent variable)
discrete data quantitative (numerical) data points that tend to be whole numbers; usually counted (e.g. number of pets)
ethics the standards used to appraise and guide what is considered acceptable conduct extrapolation predicting values outside the range of known data points, based on the existing trend fair test an experiment where all variables are kept constant except for the independent variable being tested
mean the average value, found by adding all the numbers together and dividing by the count of numbers
field work practical work conducted by a scientist in a natural environment rather than in a laboratory hypothesis an educated guess that can be tested through further experimentation; plural hypotheses independent variable the variable that is deliberately changed during an experiment inference the process of linking an observation with past knowledge and assigning meaning to the observation informed consent when participants are informed about the risks and procedures involved in an experiment and they sign to say they agree to participate interpolation the method of estimating unknown values within the range of known data points investigable question a research question that can be answered by conducting an experiment
median the middle value in an ordered data set, or the average of the two middle values if the set has an even number of observations
mode the most frequently occurring value in a data set
nominal data qualitative (categorical) data where the categories have no clear order (e.g. colours)
ordinal data qualitative (categorical) data where the categories have an order (e.g. days of the week)
outlier an anomalous data value that does not seem to fit with the rest of the data
peer review a process where work is examined and approved by experts before being published plagiarism using another person’s idea or work and pretending that it is your own precision how closely repeated measurements agree with each other
prediction a statement that describes what is expected to happen if the hypothesis is true primary data data that researchers collect themselves for a specific purpose; obtained from observations, experiments, surveys or interviews qualitative a form of data that describes characteristics or qualities about something quantitative a form of data that is a numerical measurement
randomised controlled trial a study design that randomly assigns participants to either an experimental group or a control group; the only expected difference is the variable being studied range the difference between the highest and lowest values in a data set
reliability how repeatable, replicable and reproducible the results are replicability how well the results match up when a different scientist repeats the experiment under the same conditions as the original experiment, including the same equipment and laboratory or field site reproducibility how well the results match up when a different scientist repeats the experiment under different conditions than the original experiment, including different equipment and laboratory or field site significant figures the number of digits used to indicate how accurate a measurement or calculation is systematic error an error that occurs due to a poorly calibrated device (giving consistently high or consistently low measurements)
validity the extent to which an investigation accurately measures or tests what it was intended to measure or test
action potential an electrical impulse (message) that is transmitted along a neuron
auxin a plant hormone that regulates growth and development
behavioural mechanism an action or response carried out by an organism to help maintain homeostasis and increase its chances of survival in a changing environment
chemotropism the growth of plants in response to chemicals (e.g. pollen tubes growing toward ovules during pollination)
conduction the transfer of thermal energy through collisions between particles control centre often the brain or spinal cord, which receives signals from receptors and sends out signals to effectors to produce a response to a stimulus
convection the transfer of thermal energy due to the movement of particles in a liquid or gas
ectotherm an organism that relies on external environmental sources of heat to regulate its body temperature
effector a muscle, gland or organ that carries out a response or an action in response to a stimulus
endocrine system the system of glands that controls hormones in the body
endotherm an organism that regulates its body temperature internally through metabolic processes, such as sweating, shivering or adjusting blood flow
geotropism the growth of plant parts in response to gravity, with roots growing downwards and stems growing upwards
heliotropism the movement of plant parts in response to the direction of sunlight, effectively tracking the Sun as it moves across the sky
homeostasis the process in which an organism maintains a stable internal environment despite changes in the external environment
hormone a chemical messenger that is secreted by endocrine glands and circulates in the bloodstream to act on a target cell
hydrotropism the growth of plant roots towards areas with higher moisture levels
motor neuron a nerve cell that transmits messages from the central nervous system to effectors (e.g. muscles or glands)
negative feedback a regulatory process that reduces changes in a system, bringing it back to its normal state when it deviates from its set point
integumentary the organ system that includes the skin and its associated structures such as hair, nails, sweat glands and oil glands
interneuron a nerve cell that transmits information within the brain and the spinal cord (central nervous system)
nervous system the body system consisting of the brain, spinal cord, peripheral nerves and receptors that communicate messages quickly within the body
neuron a nerve cell
neurotransmitter a chemical messenger that transmits a signal across a synapse from one neuron to another cell, which may be another neuron, a muscle cell or a gland
pathogen any agent that can cause disease, such as bacteria, viruses or fungi
phototropism the growth of plants in response to light, where plant parts grow towards or away from light sources
physiological mechanism an internal process or function carried out by the body to maintain homeostasis or respond to environmental changes radiation the transfer of energy from a source without the involvement of particles
receptor a specialised structure that allows the body to detect and respond to stimuli
reflex action a fast, involuntary motor action that protects the body from harm response the reaction to a stimulus
sensory neuron a nerve cell that transmits messages from sensory receptors to the central nervous system stimulus a change in the environment that is detected by the human body; plural stimuli synapse the junction between two neurons target cell a cell affected by a specific hormone thigmotropism the growth of plants in response to physical touch or contact, such as vines wrapping around supports tropism directional growth of a plant in response to an external stimulus
adaptation a characteristic or behaviour that enhances an organism’s ability to survive and reproduce in its specific environment
behavioural adaptations actions or behaviours that help an organism survive
Lincoln-Petersen index a statistical method used to estimate the size of a closed population
mangrove a wetland ecosystem of shrubs and trees growing in sheltered coastal areas where saltwater and fresh water mix
physiological adaptations internal processes that improve an organism’s survival
quadrat a square or rectangular frame used as a sampling tool to survey organisms in a section of an environment
structural adaptations physical features of an organism that enhance its survival
transect a straight line drawn across an ecosystem and used as a sampling tool to survey organisms
alpha particle a positively charged particle that is emitted from the nucleus of some radioactive elements during radioactive decay (disintegration) of an unstable atom
atom the building block of matter
atomic number the number of protons in an atom of an element
beta particle a negatively charged particle (electron) that is emitted from the nucleus of some radioactive elements during radioactive decay (disintegration) of an unstable atom
bioplastic a type of plastic made from renewable resources such as plants
electron a subatomic particle with a negative charge found outside the nucleus of an atom
electron shell an area around the nucleus of an atom where electrons orbit
electrostatic attraction a force pulling together oppositely charged particles
gamma ray a type of electromagnetic radiation that has high energy and a very short wavelength; produced when certain radioactive atoms decay
half-life the time taken for half of the atoms in a sample of radioactive material to decay
ion a charged version of an atom that has either gained or lost electrons
isotopes atoms of the same element with the same number of protons but a different number of neutrons mass number the sum of the protons and neutrons in the nucleus of an atom
molecule a substance generally made up of two or more non-metal atoms chemically combined
neutron a subatomic particle with a neutral charge found in the nucleus of an atom
proton a subatomic particle with a positive charge found in the nucleus of an atom
radioactive decay when an unstable nucleus emits radiation (alpha and beta particles or gamma waves) as it breaks down to form another element
relative atomic mass the average mass of an atom when considering all natural isotope masses and their abundances
nucleus the central part of the atom, containing its protons and neutrons; plural nuclei nuclide notation a symbol notation in which the mass number is shown at the top left of an element symbol and the atomic number at the bottom left
octet rule electron shells fill sequentially with 2,8,8,2 electrons
subatomic particle one of the particles that make up an atom
alkali metals group 1 metals
alkaline earth metals group 2 metals
anion a negatively charged ion
bonding pair two valence electrons that are shared between two atoms
cation a positively charged ion
chemical bond the attraction between two atoms due to the sharing of their valence electrons covalent bond formal sharing of a pair of valence electrons
covalent compound a substance made up of two or more different non-metal elements; a molecule
electron the smallest subatomic particle in an atom; electrons are arranged around the nucleus in shells
electron shell an area around the nucleus of an atom where electrons orbit
electrostatic attraction a force pulling together oppositely charged particles
element a chemical substance made up of only one type of atom
group a vertical column in the periodic table halogens group 17 elements
ionic bond an electrostatic attraction between a cation and an anion
ionic compound two or more different ions attracted by a strong electrostatic force
molecule an element or a compound containing two or more atoms combined with covalent bonds; a covalent compound
noble gases group 18 elements; also known as inert gases
octet rule electron shells fill sequentially with 2,8,8,2 electrons
period a horizontal row in the periodic table valence electrons the electrons in the outer electron shell
balanced when a chemical equation has an equal number of atoms of each element on both the reactant and the product sides of the equation
catalyst a chemical that speeds up a chemical reaction; it is not a reactant and is not used up during the reaction
chemical change a rearrangement of atoms that is often irreversible
coefficient a number placed in front of a chemical symbol to balance a chemical equation
effervescence bubbles or fizzing in solution
electrolysis a process in which an electric current is used to decompose a chemical compound law of conservation of mass a scientific law that states that matter can be neither created nor destroyed
native metal a metal that exists in its elemental form in the environment
product a substance that is formed in a chemical reaction
reactant a substance that reacts in a chemical reaction reaction conditions the conditions required for a chemical reaction to proceed rearrange move things into a different order
anthropogenic caused or influenced by humans
aquifier a body of porous rock or sediment saturated with groundwater
atmosphere the mixture of gases above the surface of Earth
biosphere all the areas on Earth and in its atmosphere that contain life
carbon sequestration the process of storing carbon in a carbon sink
carbon sink an area where carbon is stored (e.g. ocean, forests or fossil fuels)
carbon source a process or an area that releases carbon
climate the average or prevailing weather conditions of an area over long periods of time
decomposer a living organism (e.g. bacterium, fungus) that breaks down dead organic matter
global warming the long-term rise in the average temperature on Earth, primarily caused by the increase of greenhouse gases in the atmosphere
greenhouse effect the trapping of the Sun’s warmth by a layer of gases in the lower atmosphere
greenhouse gas a gas that contributes to the greenhouse effect
enhanced greenhouse effect the intensifying of the natural greenhouse effect due to human activity
evaporation the process by which water changes from a liquid to a gas
geosphere Earth’s magma, lava, rocks and minerals
glacial period a period in Earth’s history when a reduction in global temperatures is sustained for a long period of time
groundwater water that exists beneath the Earth’s surface in soil pore spaces and rock formations, typically stored in aquifers
hydrosphere all the water on Earth (e.g. lakes and rivers)
infiltration the movement of water from the surface into the soil
interglacial period a period in Earth’s history when an increase in global temperatures is sustained for a long period of time
lithosphere the geological parts of Earth’s crust and upper mantle only
percolation the downward movement of water through the soil and rock layers, often reaching groundwater precipitation the process in which water falls from the atmosphere to the Earth’s surface sphere one of Earth’s major systems (atmosphere, hydrosphere, lithosphere and biosphere), which interact to support life and shape the planet sustainable ecosystem a biological environment that can support itself without outside assistance trade winds permanent winds that blow steadily towards and along the equator from east to west transpiration the release of water vapour from plants into the atmosphere weather the atmospheric conditions (such as temperature, cloud, rain or wind) at a particular time over a particular area
accommodation automatic adjustments made by the eye when looking at objects at different distances amplitude the distance (height) of a wave crest or the depth of a wave trough from the centre line of the wave
angle of incidence the angle between an incident light ray and the normal, when the ray arrives at a surface
angle of reflection the angle between a reflected light ray and the normal, when the ray leaves a surface
auditory nerve the nerve that connects the ear with the brain
ciliary muscle a muscle in the eye that controls the focus of the lens by changing its shape
choroid a layer of blood vessels in the eye that supply the retina
cochlea a spiral tube inside the inner ear that produces nerve impulses in response to sound waves; the main organ of hearing compression the part of a longitudinal wave where the particles are squashed together
concave for a lens, having an outline that is thinner in the middle; for a mirror, curved inwards, like a cave convex for a lens, having an outline that is thicker in the middle; for a mirror, bulging outwards
cornea the transparent outer covering of the eye
crest the maximum displacement of a particle at the top of a wave
cycle one complete vibration or periodic movement of a particle through the crest and trough and back to its starting position; the length of a cycle is the wavelength
displacement the position of a particle when it has moved away from its rest position on the centre line of a wave
ear canal a tube that connects the outer ear and the middle ear
eardrum a thin piece of membrane inside the ear that moves backwards and forwards very quickly (vibrates) when sound waves reach it
electromagnetic radiation the transfer of energy by electromagnetic waves
electromagnetic wave a wave with electric and magnetic components that can travel through matter or a vacuum
fovea a small part of the retina that contains the most light-sensitive cells frequency the number of cycles of a wave per second; measured in hertz (Hz)
gamma ray a type of electromagnetic radiation that has high energy and a very short wavelength; produced when radioactive atoms decay
hertz a unit for measuring the number of cycles that happen every second (frequency); abbreviation Hz
incident ray a ray of light arriving at a surface infrared radiation a type of electromagnetic radiation between microwaves and visible light; also known as heat radiation
lens (eye) a small disc of transparent tissue behind the pupil that allows the eye to focus on near and far objects
longitudinal wave a wave with vibrations in the direction of travel instead of transversely; e.g. sound waves
ionising radiation higher-frequency ultraviolet rays, X-rays and gamma rays, which can turn atoms and molecules into ions, which can damage living cells iris the coloured circular part of the eye that surrounds the pupil
lens a glass disc used to make images with light; a convex lens makes both enlarged and smaller images; a concave lens makes a smaller image
long-sighted able to see distant things clearly, but not things that are close
mechanical wave a disturbance in a medium that transfers energy through that medium medium the matter through which a mechanical wave travels
microwave a type of electromagnetic radiation used for cooking, communications and Wi-Fi; lies between radio waves and infrared radiation
normal an imaginary line that is at right angles to a surface
optic nerve the nerve that connects the eye with the brain
oscillating moving back and forth with periodic motion somewhat like vibration
period the time, in seconds (s), taken for a wave to complete one cycle
periodic motion the movement of a particle or an object that returns to its starting position and repeats in the same time interval, like a swing photon an electromagnetic wave carrying a specific amount of energy related to its frequency or wavelength pitch how high or low a sound seems to our ears on a music scale
plane mirror a flat reflective surface
prism a piece of glass with a triangular crosssection that can be used to separate white light into its colours
pupil the circular black area in the centre of the eye through which light enters radio wave a type of electromagnetic radiation that has the longest wavelength rarefaction the part of a longitudinal wave where the particles are spread apart reflect change direction (of a wave) when hitting a surface boundary, so the wave continues to travel in the same medium
reflected ray a ray of light that is reflected off a surface
refraction the bending of light as it passes from one medium to another
refractive index a measure of how much the speed of light changes as it passes from a vacuum into a particular substance
resonance frequency the natural frequency of vibrating particles in an object
retina an area of tissue at the back of the eye that contains cells that detect light and colour sclera the white outer layer of the eyeball seismic wave a wave that travels through Earth and over its surface and is caused by earthquakes self-propagating refers to a wave that (unlike mechanical waves) keeps going at a constant speed forever without needing the input of more energy short-sighted able to see close things clearly, but not things that are far away transverse wave a wave in which the particles vibrate or move at right angles (perpendicular) to the direction of energy transfer trough the maximum displacement of a particle at the bottom of a wave
ultraviolet light a type of electromagnetic radiation between visible light and X-rays; needed by our bodies to make vitamin D; short wavelength ultraviolet light can cause sunburn and cancer vacuum a space completely devoid of matter visible light the part of the electromagnetic spectrum that we can see vitreous humour the clear jelly-like substance in the eyeball through which light passes wave a carrier of energy that travels through space or matter without the movement of matter as a whole wavelength the distance from one wave crest to the next; measured in metres (m)
X-ray a type of electromagnetic radiation that has short wavelengths and can pass through flesh to give images of bones; hazardous and can cause cancer