Edexcel international gcse science biology sample chapter

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Student Book

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EDEXCEL INTERNATIONAL GCSE (9-1) BIOLOGY

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Jackie Clegg, Sue Kearsey, Gareth Price and Mike Smith

Contents

a) Characteristics of living organisms.................10 b) Variety of living organisms................................15 c) Exam-style questions...........................................25

Section 2 Structure and functions in living organisms..................28

Section 5 Use of biological resources......................320

a) Food production....................................................322 b) Selective breeding................................................342 c) Genetic modification (genetic engineering)..........................................350 d) Cloning.....................................................................359 e) Exam-style questions...........................................367

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a) Level of organisation............................................30 b) Cell structure..........................................................36 c) Biological molecules.............................................43 d) Movement of substances into and out of cells...............................................................55 e) Nutrition...................................................................68 f) Respiration...............................................................97 g) Gas exchange.........................................................105 h) Transport..................................................................124 i) Excretion....................................................................148 j) Coordination and response................................157 k) Exam-style questions...........................................177

a) The organism in the environment..................256 b) Feeding relationships..........................................268 c) Cycles within ecosystems...................................283 d) Human influences on the environment........293 e) Exam-style questions...........................................311

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Section 1 The nature and variety of living organisms......................8

Section 4 Ecology and the environment................254

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Getting the best from the book............................4

Section 3 Reproduction and inheritance.............188

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a) Reproduction..........................................................190 b) Inheritance..............................................................214 c) Exam-style questions...........................................248

The International GCSE examination....374 Overview.......................................................................374 Assessment objectives and weightings.............375 Examination tips.........................................................375 Answering questions................................................378

Developing experimental skills..............380 Planning and assessing the risk............................380 Carrying out the practical work safely and skilfully......................................................386 Making and recording observations and measurements....................................................390 Analysing the data and drawing conclusions...................................................................393 Evaluating the data and methods used.............400

Mathematical skills....................................404

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Glossary.........................................................................406 Answers..........................................................................415 Index...............................................................................000

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Around 1.9 million living species have been described and named on Earth. Around 350 000 of these species are classified as plants and around 1.37 million species are classified as animals. Over 66 000 of the animal species are vertebrates (they have bony skeletons), and the rest are invertebrates of which the majority (around 1 million species) are insects.

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It is difficult to know how many species are still to be discovered, although scientists reckon they have discovered most living mammals, birds and coniferous trees. The smaller the organism, the greater the chance that there are species we don’t yet know about.

So although over 4000 species of bacteria have been identified, there could be more species of bacteria than of all the other kinds of organisms put together.

STARTING POINTS 1. What are the characteristics shared by living organisms?

2. Crystals can grow in size, but does that mean they are alive?

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3. We talk of ‘feeding’ a fire when we add fuel, but does that mean fire is a living thing?

4. Why is it useful to group organisms?

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5. What features are the most useful for grouping organisms?

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CONTENTS a) Characteristics of living organisms b) Variety of living organisms

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c) Exam-style questions

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The nature and variety of living organisms

∆∆Many species of different kinds of organisms live on a coral reef.

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Characteristics of living organisms INTRODUCTION

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∆∆Fig. 1.1 Tiny tardigrades (about 1 mm long) are one of the toughest organisms known. They can survive temperatures below –200 °C, 10 days in the vacuum of space and over 10 years without water!

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Sometimes it is easy to tell when something dies: an animal stops moving around; a plant wilts and all the green parts collapse. But does a tree die in winter, when its leaves have dropped off? Are animals ‘dead’ when they hibernate underground for months?

As technology gets increasingly sophisticated, and we can create machines with ‘brains’ and grow new organs in a laboratory, distinguishing between living and non-living could get even more difficult. We need a set of ‘rules’ that work for most organisms, most of the time.

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KNOWLEDGE CHECK ✓✓Living organisms show a range of characteristics that distinguish them from dead or ­non-​­living material. ✓✓The life processes are supported by the cells, tissues, organs and systems of the body.

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LEARNING OBJECTIVES ✓✓Name the eight characteristics shown by living organisms. ✓✓Describe each of the characteristics of living organisms. ✓✓Explain that not all living organisms show every characteristic all of the time.

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THE EIGHT CHARACTERISTICS OF LIFE There are eight life characteristics that most living organisms will show at some time during their lives.

• Movement: In all living cells, structures in the cytoplasm move. In more complex organisms, the whole structure may move. Animals may move their entire bodies; plants may move parts of their body in response to external stimuli ∆∆Fig. 1.2 Sunflowers follow the Sun as it moves across the sky through the day. such as light.

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• Respiration: This is a series of reactions that take place in living cells to release energy from nutrients. This energy is used for all the chemical reactions that keep the body alive.

• Sensitivity: Living organisms are able to detect and respond to changes in their external and internal conditions.

• Homeostasis: This is the control of internal conditions, to provide the best conditions inside cells for all the reactions needed for life to exist. For example, when we eat and drink we take in water – our body controls how much water is absorbed and removed from the blood, so that cell processes can continue to work efficiently.

• Growth: This is the permanent increase in the size and/or dry mass (mass without water content) of cells or the whole body of an organism. Your mass changes throughout the day, depending on how much you eat and drink, but your growth is the amount by which your body increases in size when you take nutrients into cells to increase their number and size. As organisms grow, they may also change or develop.

• Reproduction: This includes all the processes that result in making more individuals of that kind of organism, such as making gametes and the fertilisation of those gametes.

• Excretion: Living cells produce many products from the reactions that take place inside them. Some of these are waste products – materials that the body does not use. For example, animals cannot use the carbon dioxide produced during respiration. Waste products may also be toxic, so they must be removed from the body by excretion.

• Nutrition: The taking of nutrients, such as organic substances and mineral ions, into the body. Nutrients are the raw materials that cells need to release energy and to make more cells.

QUESTIONS

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1. For each of the eight characteristics, give one example for: a) a human

b) an animal of your choice

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c) a plant.

2. For each of the eight characteristics, explain why they are

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essential to a living organism.

Remember

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An easy way to remember all eight characteristics is to take the first letter from each process. This spells MRS H GREN. Instead, you may make up a sentence in which each word begins with same letter as one of the processes: for example, My Revision System Here Gets Really Entertaining Now.

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EXTENSION

DNA

∆∆Fig. 1.3 The structure of a virus.

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Not everyone agrees on whether viruses can be called living organisms.

protein coat

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Viruses are very simple structures, consisting of an outer protein coat that protects the genetic material inside. They have no cell structures or cytoplasm, so they do not respire or sense their surroundings.

They also do not take in substances to build more cells, or excrete anything. In many ways they behave like simple crystalline chemicals. However, when they infect a cell, such as a bacterial, plant or animal cell, they cause that cell to produce many copies of the virus. So they do reproduce.

1. Which characteristic of living organisms do viruses have?

2. List the other characteristics of living organisms, and for each one describe what viruses can and cannot do.

3. Using what you know about viruses, prepare an argument for classifying them as living organisms.

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Remember

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4. Using what you know about viruses, prepare an argument for not classifying them as living organisms.

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Be prepared to make a decision and use your knowledge to argue your point of view about difficult examples such as viruses.

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End of topic checklist Excretion is the removal of waste (often toxic) substances that have been produced from chemical reactions inside the body, such as carbon dioxide and urea in animals.

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Growth is the permanent increase in body size and dry mass of an organism, usually from an increase in cell number or cell size (or both).

Homeostasis is the maintenance of a constant internal environment, such as body water content and body temperature.

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Movement happens in all living cells: both plants and animals.

Nutrition is the taking in of substances for use in the body as food or to make food.

Reproduction is the production of new organisms.

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Respiration is the chemical process in which glucose is broken down inside cells, releasing energy and producing carbon dioxide and water.

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Sensitivity refers to the detection of changes (stimuli) in the surroundings by a living organism, and its responses to those changes.

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The facts and ideas that you should know and understand by studying this topic:

❍❍All living organisms show the eight characteristics of life at some point in their lives.

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❍❍The characteristics of life are: movement, respiration, sensitivity, homeostasis,

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growth, reproduction, excretion and nutrition.

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End of topic questions 1. Name the eight processes of life. Try making up your own sentence to help you (9 marks) remember them all.

(2 marks)

3. Explain why dry mass is used to measure growth.

(2 marks)

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2. Name two life processes necessary for an organism to release energy.

4. When you place a crystal of copper(II) sulfate in a saturated solution of the same compound, the crystal will increase in size. Does this mean that the crystal is alive?

(1 mark) Explain your answer.

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5. Plants cannot move about, as animals can. Does that mean animals are more alive (2 marks) than plants? Explain your answer.

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6. During winter, an oak tree will lose its leaves and not grow. Is the tree still living during this time? Explain your answer using all the characteristics of life.

(4 marks)

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Variety of living organisms

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The many different kinds of living organisms come in a confusing variety of forms.

Classifying (grouping) organisms using their similar characteristics helps us to make sense of all the variation. This information can help us understand which organisms are most closely related to each other, which groups have evolved from other groups, and which groups play the most important roles in an ecosystem.

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INTRODUCTION

∆∆Fig. 1.4 The tallest plants are giant redwood trees, capable of growing to over 90 m high.

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KNOWLEDGE CHECK ✓✓Living organisms show great variety. ✓✓Organisms can be classified according to their characteristics.

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LEARNING OBJECTIVES ✓✓Describe the common features shown by eukaryotic organisms: plants, animals, fungi and protoctists. ✓✓Describe the common features shown by prokaryotic organisms such as bacteria. ✓✓Understand the term pathogen and know that pathogens may include fungi, bacteria, protoctists or viruses.

PLANTS Plants are multicellular organisms, which means they are made up of more than one (usually thousands or millions) of cells.

Plant cells have a cell wall as well as a cell membrane. The cell wall is made of cellulose and gives the cell shape and support.

Many plant cells have a large central vacuole that contains cell sap, which is water with various substances dissolved in it. The vacuole may

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EUKARYOTES AND PROKARYOTES Living organisms are either eukaryotic or prokaryotic. Eukaryotic organisms have cells that contain a nucleus and other organelles such as mitochondria and chloroplasts. Plants, animals, fungi and protoctists are all eukaryotic organisms. Prokaryotic organisms have cells that are much smaller and simpler than eukaryotic cells.

Prokaryotic cells do not contain a nucleus or organelles such as mitochondria or chloroplasts. Bacteria are prokaryotic organisms.

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also be a storage space for some substances. In a healthy plant the vacuole is large and helps support the cell when it is full of sap.

Plant cells may contain chloroplasts, which are able to carry out photosynthesis – a process in which they use the Sun’s energy to produce carbohydrates. Carbohydrates, stored as starch or sucrose, store energy for the plant but can also be used as food by animals that eat plants.

Plants vary greatly in size and shape, from tall rainforest trees to tiny flowers like violets. We use many plants as food, including cereals such as rice and maize, and herbaceous legumes such as lentils, peas and beans.

QUESTIONS

1. Explain what is meant by the term multicellular, and give one

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example.

2. Plants do not have skeletons, as animals do, but are still able to stand upright. Explain why.

3. One kind of structure found in some plant cells makes plants

able to produce their own food. What is this structure called?

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ANIMALS Animals are multicellular organisms. Unlike plants, their cells do not contain chloroplasts and so cannot carry out photosynthesis. This means that they have to eat other organisms (plants or other animals) to get their food. Animal cells have a cell membrane but no cell wall. Many animals are able to coordinate their movement using nerves and are able to move from one place to another. For energy, animals also store carbohydrates, often in the form of glycogen. They also store lipids, often as a layer of fat below the skin or around body organs, as a store of energy.

As with plants, the variety of animals is huge, from enormous whales and elephants to tiny ants.

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▷▷Fig. 1.5 Ants belong to the insects, as do the housefly and mosquito. Whales and elephants are classified as mammals, as are humans.

QUESTIONS 1. If you compared a plant cell and an animal cell under the ­microscope, which features would you see:

a) in both cells 16

b) only in the plant cell?

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2. Describe two differences between plants and animals in terms of the structure of their bodies.

3. One difference between plants and animals is that many animals can move from place to place, but plants cannot. Explain this difference.

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bud (this is how the cell multiplies, bits bud off as separate daughter cells)

nucleus

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2 µm

cell wall

vacuole

mitochondrion

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FUNGI Some fungi (such as yeast) are ­single-​­celled but most have a structure consisting of fine threads known as hyphae. Each hypha may contain many nuclei. Several hyphae together form a mycelium. Many fungi can be seen without a microscope. Their cell walls are made of chitin, a fibrous carbohydrate which is different to the cellulose used in plants.

Their cells do not contain chlorophyll so they cannot carry out photosynthesis. To obtain energy they secrete digestive enzymes outside the cells (extracellular secretion), onto living or dead animal or plant material, and absorb the digested nutrients. This is called saprotrophic nutrition. Like animals, fungi may store carbohydrate in the form of glycogen.

200 m

cell membrane

∆∆Fig. 1.6 The internal structure of a yeast cell that is reproducing by budding.

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spore case

yeast cell

wall of chitin

cell membrane vacuole

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nuclei

hyphae forming mycelium

part of fungal hypha

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Mucor

cytoplasm

∆∆Fig. 1.7 Left: the mycelium and spore cases of Mucor, a mould. Right: detail of a hypha of Mucor.

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Examples of fungi include yeast, a ­single-​­celled fungus used by humans in baking, and Mucor, a fungus with the typical hyphal structure. Mucor is often seen as a mould growing on spoiled foods.

Some species of fungi are pathogens, which means they cause disease in other organisms. For example, ringworm is caused by a fungus that produces rings of itchy skin in humans. Also many plants are damaged by rusts and moulds which are different kinds of fungi.

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Mushrooms and toadstools

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We normally think of a mushroom and toadstool as the whole of a fungus, because this is usually all we can see.

However, these are only the reproductive organs, where spores are produced. The mycelium of the fungus is usually hidden below ground or within rotting materials, where it is moist and where the hyphae can digest the surrounding tissue and absorb the nutrients that are released. The reproductive structures have to be large enough so that the wind can carry the spores away to other places, and tough enough to survive the drying conditions of the air until the spores have been dispersed.

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● SCIENCE IN CONTEXT

▷▷Fig. 1.8 A mushroom or toadstool is only the visible part of this fungus. The rest of the structure is hidden from view.

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QUESTIONS

1. Which characteristics do fungi share with a) plants and

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b) animals?

2. Describe what is meant by saprotrophic nutrition and how

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it differs from the way animals get their nutrition.

3. Most people think of toadstools and mushrooms as the main part of fungi. Explain why this is incorrect.

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PROTOCTISTS Protoctists are also ­single-​­celled microscopic organisms, usually much larger than bacteria. Their cells contain a nucleus and many have features of animal cells or plant cells. One example is Amoeba, which looks like an animal cell and is found in ponds and feeds on other microscopic organisms. Other protoctists, such as Chlorella, look more like plant cells because they contain chloroplasts and so can photosynthesise. A few protoctists are pathogens, such as Plasmodium, the organism that causes the disease malaria in humans.

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nucleus

cell wall cell membrane

cell membrane chloroplast

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nucleus

food vacuole contractile vacuole

∆∆Fig. 1.9 Amoeba and Chlorella.

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● SCIENCE IN CONTEXT

Malaria

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Malaria is one of the greatest causes of death from infectious illness in the world today. Around 750 000 people die of the disease each year, mostly young children and mostly in ­sub-​­Saharan Africa. The disease is caused by the protoctist Plasmodium, which has a clever way of getting from one person to the next: it hitches a lift in the alimentary canal of an Anopheles mosquito. The female mosquitoes suck blood from humans to provide the nutrients they need to lay eggs. As a mosquito pierces into a blood vessel, it inserts a little liquid to prevent the blood from clotting. If the mosquito has fed recently on a person infected with Plasmodium, this liquid will contain some of the parasites and so infect the new person. This protects the protoctist from the harsh conditions of the environment and allows it to be passed on to a new host.

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QUESTIONS

1. Explain why some protoctists were once classified as plants and others as animals.

2. What features do all protoctists have in common?

Explain your answer.

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3. Is it correct to describe mosquitoes as the cause of malaria?

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BACTERIA Bacteria are ­single-​­celled, microscopic organisms that are smaller than plant and animal cells and come in many different shapes. Their cells have no nucleus, so the single circular chromosome of DNA lies free in the cytoplasm inside the cell. Many bacteria have additional circles of genetic material, called plasmids.

Bacterial cells are surrounded by a cell membrane and cell wall, although in different groups of bacteria the cell wall is made of different chemicals. Some bacteria can carry out photosynthesis but most feed ∆∆Fig. 1.10 General structure of a bacterial cell. off other living or dead organisms.

Some bacteria are useful to humans. For example, Lactobacillus bulgaricus, a ­rod-​­shaped bacterium, is used to make yoghurt from milk.

Other bacteria are pathogens, causing diseases in plants and animals.

An example of a pathogen is Pneumococcus, a spherical bacterium that can cause pneumonia in humans.

Azotobacter

Salmonella

Spirillum

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Staphylococcus

● SCIENCE IN CONTEXT

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∆∆Fig. 1.11 Different bacteria can be recognised from their shape and structure.

Bacterial plasmids

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Bacterial plasmids have become very useful to us in genetic engineering, where they are used as vectors (see Topic 5c: Genetic modification (genetic engineering)). Not all bacteria have them, but those that do transfer these small circles of genetic material to other bacteria quite easily. Plasmids may even be transferred between bacteria of different species. This is not true reproduction as the transfer is not of the main chromosome and may not lead to production of new individuals.

However, this kind of transfer may be important in the spread of antibiotic resistance between bacterial species, because some of the genes for antibiotic resistance are found in the plasmids.

QUESTIONS 1. Describe three differences between a plant cell and a bacterial cell.

2. Compare the structure of bacteria and protoctists.

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3. How are bacterial chromosomes different from the chromosomes of eukaryotes?

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