Bring Science Alive! 6th Grade Integrated Segment 2

6th Grade Integrated

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CONTENTS

Next Generation Science Standards for Three Dimensional Learning...............xxx Dimension 1: Science and Engineering Practices.............................................xxxii Dimension 2: Crosscutting Concepts................................................................xxxiv Dimension 3: Disciplinary Core Ideas...............................................................xxxvi Integrating Engineering with Science Learning.............................................xxxviii Considerate Text.................................................................................................... xl

Integrated Segment 1 Systems and Subsystems in Earth and Life Science.. . . . . . . 2 Integrated Phenomenon Sometimes, people get sunburned skin from a day at the beach.

Developing a Model Explore the systems that cause this phenomenon—from large systems like planet Earth to tiny systems in the cells that make up your body. Develop an initial model to explain the phenomenon, then revise the model as you go through the segment.

The Atmosphere and Energy............................................................... 6 Anchoring Phenomenon Cold food in a cooler stays cold, and food in a solar cooker gets hot.

Phenomenon-Based Storyline The Extreme Adventures Company has hired you to design equipment to help adventurers stay healthy and safe in extreme weather conditions.

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Earth’s Atmosphere...................................................8 Phenomenon Breathable air exists only in the lowest 5 km of Earth’s atmosphere.

Investigations Journey to the exosphere to gather and graph data on each layer of the atmosphere.

Key Science Concept: Earth’s Troposphere

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Taking Earth’s Temperature...................................... 16 Phenomenon Ice melts faster on some surfaces than others.

Investigations Build a thermometer, then use it to test a variety of items to determine which are insulators and which are conductors.

Key Science Concept: Thermal Energy and Changes in Temperature

Engineering Challenge: Minimizing and Maximizing the Rate of Heat Transfer The Extreme Adventures Company is holding a contest for the best cooler and the best solar oven. Design a device to either minimize or maximize heat transfer.

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Earth and Solar Energy. . .......................................... 28 Phenomenon The surface temperature on Venus is 464 °C, which is hot enough to melt lead.

Investigations Build an atmospheric model that simulates the greenhouse effect to predict planets' temperatures.

Key Science Concept: How the Sun Heats Earth

Performance Assessment: Surviving Extreme Temperatures Develop a proposal to improve a cooler or solar cooker based on revised criteria and constraints, applying key scientific principles to optimize the design.

Cells................................................................................................38 Anchoring Phenomenon A bacterial cell, created in a biology laboratory, has no parent.

Phenomenon-Based Storyline As a technician in a biology lab, you have been tasked with creating a model of a synthetic animal or plant cell and devising a test to determine if synthetic organisms are truly alive.

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Cell Theory............................................................. 40 Phenomenon People once believed that mice could be generated from dirty shirts in bags of wheat.

Investigations Observe that all living things are made of cells and discover the unicellular organisms that live all around you.

Key Science Concept: Cell Theory Applies to Unicellular and Multicellular Organisms

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Parts of Cells.......................................................... 48 Phenomenon Many cells, like this paramecium, can move around and fulfill their needs without legs or body systems.

Investigations Discover different parts of cells and act out the mechanisms that allow cells to absorb nutrients and get rid of waste.

Key Science Concept: Comparing Models of Animal and Plant Cells | Controlling What Enters and Leaves a Cell

Performance Assessment: Modeling Synthetic Cells Create a model to prototype the development of a synthetic cell and develop an investigation that will determine whether a synthetic cell is a living thing.

Segment Wrap Up.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Using Your Model to Explain the Phenomenon Return to the model you developed at the beginning of the segment, and revise it based on what you learned about the atmosphere, energy, and cells. Then, use your model to explain the Integrated Phenomenon.

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Integrated Segment 2 Earth Systems, Weather, and Organisms.. . . . . . . . . . . . . . . . . . . . . . . 64 Integrated Phenomenon When a person takes a dog on a long walk in the summer, you might see that the person is sweating but the dog is panting.

Developing a Model Explore the traits and body systems that help organisms like you stay comfortable during hot or cold weather. Develop an initial model to explain the phenomenon, then revise the model as you go through the segment.

Weather......................................................................................... 68 Anchoring Phenomenon Severe weather events can lead to extreme loss of life and property.

Phenomenon-Based Storyline As part of the National Oceanic and Atmospheric Administration (NOAA), your task is to develop instruments for measuring atmospheric conditions, interpret weather maps, make weather forecasts, issue severe weather warnings, and create severe weather action plans.

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Air Pressure and Wind............................................. 70 Phenomenon Some days are windy, and some are not.

Investigations Build your own barometer and predict weather patterns across the United States.

Key Science Concept: Sea and Land Breezes

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Water and the Weather............................................ 82 Phenomenon When warm air rises and then cools, clouds form in the sky.

Investigations Construct a psychrometer to measure humidity, then develop a model of the water cycle.

Key Science Concept: Energy and the Water Cycle

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Air Masses and Changing Weather........................... 96 Phenomenon Suddenly on a warm day, a cool wind begins to blow, clouds form, and the temperature drops by ten degrees.

Investigations Collect local weather data, model different fronts using cold and warm water, and interpret weather maps.

Key Science Concept: Relating Air Masses, Fronts, and Pressure Systems

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Severe Weather. . ................................................... 108 Phenomenon There are more tornadoes in the Great Plains than anywhere else in the United States.

Investigations Predict severe weather by analyzing weather maps.

Key Science Concept: Severe Weather Safety

Performance Assessment: Severe Weather Action Plan Gather weather data and make forecasts, then propose recommendations to the city council for developing methods that can mitigate the dangers of any severe weather events you have forecasted.

Traits............................................................................................ 120 Anchoring Phenomenon Organisms have unique physical and behavioral traits that help them survive.

Phenomenon-Based Storyline Plan an eco-tour of Madagascar, an island that has many plants and animals that exist nowhere else on the planet, and highlight how the unique traits of Madagascar's organisms have helped them survive.

10 Traits for Survival.................................................. 122 Phenomenon Humans have opposable thumbs, but turtles do not.

Investigations Gather evidence from a variety of media about specialized plant and animal traits and explain how these traits increase organisms' chances of survival.

Key Science Concept: Physical Traits for Survival

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11 Traits for Reproduction.......................................... 136 Phenomenon The blue-footed booby has bright blue feet that the males show off by strutting in front of the females.

Investigations Use evidence about traits that increase an organism's chance for survival and reproduction to compare arguments explaining why one species, the elephant bird, did not survive.

Key Science Concept: Traits, Mates, and Offspring

Engineering Challenge: Designing a Seed Dispersal Device Nana wants to plant a wildflower garden in the lot across the street. Help her by designing, building, testing, and modifying a device that mimics how plants disperse seeds in nature.

Performance Assessment: Planning a Trait Trek to Madagascar Plan a Trait Trek to Madagascar and design a brochure for your travelers that demonstrates how each organism's unique traits help it survive and reproduce.

Bodies........................................................................................... 148 Anchoring Phenomenon People become sick when body systems don't function properly.

Phenomenon-Based Storyline Every day, people all over the world get sick. Sometimes they recover; sometimes they don’t. Like a doctor, use evidence from medical charts, test results, and medical fact sheets to "diagnose" four patients.

12 Interacting Body Systems. . .................................... 150 Phenomenon Doctors know generally what is inside a living person's body without having to cut them open.

Investigations Dissect a frog to learn about body systems, create a lifesize human body model for your doctor's office, and diagnose your first patient, Mr. T. Key Science Concept: Interactions Among Body Systems

Engineering Challenge: Designing a Prosthetic Hand People born without a functioning hand or those who lost the functioning of a hand later in life could benefit from an engineer-designed substitute—a prosthetic hand. Design, build, test, and modify a prosthetic hand to execute a specific function.

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13 Levels of Organization. . ......................................... 166 Phenomenon Body systems, like the skeletal system, are made of smaller and smaller parts.

Investigations Observe and interpret tissue samples under a microscope to help diagnose another patient, Ms. B. Key Science Concept: Levels of Organization in the Body

14 Controlling Body Systems..................................... 178 Phenomenon Sometimes people lose their coordination or memory.

Investigations Add the nervous system to your lifesize human body models, then use your knowledge of the nervous system's functions to diagnose Ms. K. Key Science Concept: Stimuli and Responses While Cooking

Performance Assessment: Diagnosing JJ Diagnose your fourth patient, JJ, using your knowledge of body systems and information processing.

Segment Wrap Up.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Using Your Model to Explain the Phenomenon Return to the model created at the beginning of the segment, and revise it based on what you learned about weather, traits, and bodies. Then, use your model to explain the Integrated Phenomenon.

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Integrated Segment 3 Regional Climates, Global Warming, and Living Systems.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 Integrated Phenomenon Scientists have genetically modified soybeans to be drought-resistant.

Developing a Model Explore genes and climate to better understand how humans can change crops to become more resilient to extreme climates. Develop an initial model to explain the phenomenon, then revise the model as you go through the segment.

Climate.......................................................................................... 198 Anchoring Phenomenon From 1880 to 2016, Earth's average temperature increased by 0.95°C. Phenomenon-Based Storyline The rise in average global temperature majorly impacts rising sea level, changing weather patterns, and the disruption of ecosystems. Design a plan that mitigates and/or adapts to one of these factors of climate change.

15 Climate Patterns................................................... 200 Phenomenon Earth’s surface is warmer at the equator than it is at the poles.

Investigations Model how the sun's light strikes Earth's surface and analyze climographs to play a quiz game.

Key Science Concept: Climate Controls: Latitude, Elevation, Nearness to Water

16 Global Circulation of the Atmosphere. . ................... 212 Phenomenon The Sooty Shearwater’s yearly migration follows the same figureeight pattern each time.

Investigations Model the Coriolis Effect and global wind patterns, then use what you know to plot routes for a shipping company.

Key Science Concept: Uneven Heating of Earth Produces Global Winds

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17 How the Ocean Affects Climate.............................. 222 Phenomenon The ocean water along the southern California coastline is colder than the ocean water along the South Carolina coastline, despite being at the same latitude.

Investigations Create a plan to monitor ocean temperatures using buoys, then model global circulation and ocean energy flow.

Key Science Concept: Ocean Currents and Climate

18 Local Climate. . ...................................................... 234 Phenomenon The local climates on either side of a mountain are different.

Investigations Explore the effects of albedo using colored paper, then use climographs and maps to explain climate differences in similar locations.

Key Science Concept: Postcards from Colorado: Colorado’s Local Climates

Engineering Challenge: Designing a Microclimate How can you grow a plant that is non native to your local environment? Design and develop a growth system that maintains its own microclimate to help the plant grow.

19 Earth’s Climate Over Time...................................... 246 Phenomenon During the past 100 years, Earth’s average global temperature has risen by about 0.7 °C. Investigations Create a timeline of Earth's history and explain changes in the average global temperature over the past 100 years.

Key Science Concept: Climate Change in Modern Times

20 Climate Today and Tomorrow.. ................................ 258 Phenomenon Since 1979, the average yearly minimum size of the ice cap at the North Pole has decreased by about 40 percent.

Investigations Become experts on the effects of climate change and propose a plan to adapt to the effects.

Key Science Concept: Effects of a Warming Atmosphere

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Performance Assessment: Mitigating and Adapting to Climate Change Join a team of scientists to describe the threats that a city's regional climate faces from climate change, then create a plan to mitigate or adapt to climate change.

Genes............................................................................................ 274 Anchoring Phenomenon Some organisms look exactly like their parents and others do not.

Phenomenon-Based Storyline Coral reefs around the world are threatened by rising ocean temperatures. Working as an official at a National Park, you have been asked to devise a management plan to save local coral reefs.

21 Proteins, Genes, and Chromosomes....................... 276 Phenomenon Some cats have short, orange hair and some cats have long, grey hair.

Investigations Model the relationship between DNA, genes, and chromosomes to discover how genes lead to traits.

Key Science Concept: Modeling the Causes of the Eye Color Trait

22 Inheriting Genes................................................... 288 Phenomenon Some organisms, like bacteria, are identical to their parents but other organisms, like dogs, are not.

Investigations Predict how asexual and sexual reproduction will lead to different inherited trait combinations and use Punnett Squares to model how alleles and traits are inherited.

Key Science Concept: Explaining Mendel’s Observations Using Punnett Squares | Predicting Ear Wax Texture with a Punnett Square

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23 Genes and the Environment.................................. 304 Phenomenon Identical twins look similar but not exactly alike.

Investigations Design experiments that test the roles of genes and the environment in determining plant growth.

Key Science Concept: Both Genetic and Environmental Factors Can Affect Traits

Performance Assessment: Conserving Coral Reefs Using Genetics In order to save coral reefs in a marine park, design a management plan using your knowledge of coral reproduction, allele combinations, and genetic inheritance.

Changes in Genes........................................................................... 312 Anchoring Phenomenon An organism's traits can be altered by a change in its genes.

Phenomenon-Based Storyline Organisms' traits are altered when their genes are changed by mutations or genetic engineering. Critique articles about mutations and genetic engineering by assessing the reliability of each article's source.

24 Genetic Mutations................................................ 314 Phenomenon Some people have six fingers on one hand and some grapefruit are bright red.

Investigations Model how mutations can affect the function of a protein by changing its structure, then explore different types of mutations.

Key Science Concept: Effects of Mutations

Engineering Challenge: Designing a Dog Breeding Process A family is looking for a specific type of dog but cannot find a breed that fits their needs. Design criteria for how to breed a new type of dog using artificial selection techniques.

25 Engineering and Genetics. . .................................... 324 Phenomenon Before the 1990s, there were no glow-in-the-dark mice, but now there are many kinds of glow-in-the-dark mice.

Investigations Debate the pros and cons of different genetic engineering techniques.

Key Science Concept: Solving a Problem in Living Systems Using the Engineering Process

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Performance Assessment: Investigating Genetic Engineering Present a news story on genetic engineering techniques and their potential consequences after researching story leads.

Segment Wrap Up.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Using Your Model to Explain the Phenomenon Return to the model created at the beginning of the segment, and revise it based on what you learned about climate, genes, and changes in genes. Then, use your model to explain the Integrated Phenomenon.

Learning Resources ......................................................338

Mathematics in Science..............................................380

Science and Engineering Safety..................................340

Measurement Units.....................................................390

Science and Engineering Practices..............................344

Glossary...........................................................................394

Crosscutting Concepts.................................................364

Index.................................................................................400

Literacy in Science.......................................................372

Credits..............................................................................413 xix

SEGMENT 2

Earth Systems, Weather, and Organisms

INTEGRATED PHENOMENON When a person takes a dog on a long walk in the summer, you might see that the person is sweating but the dog is panting.

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Connecting to Local Phenomena Why would you check the weather? You might check the weather because it affects decisions you make and what activities you do over the course of the day. Organisms, including you, have traits and body systems to help make them comfortable in hot or cold weather. Understanding weather, traits, and body systems can help you answer these questions and explain other phenomena.

Sometimes, it’s tough to stay comfortable when the weather gets too hot. Luckily, your body has some systems built in to help you stay cool. What are some ways your body cools down when it gets hot?

Down feathers on geese help keep them warm in cold weather. Their feathers have influenced the development of artificial down jackets, which have many of the same properties as geese feathers. How can we design devices based on traits of other organisms to help us in cold or warm weather?

You may see a dog panting on a hot day to stay cool. What traits do cats have to stay cool?

Developing a Model What questions do you have about the Integrated Phenomenon, and how might you investigate to find answers?

Use what you know to develop a rough model of this phenomenon. As you go through each lesson in this segment, return to this model to revise and develop it.

E a r t h S y s t e m s , We a t h e r , a n d O r g a n i s m s

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Segment Overview In this segment, you will explore why a person sweats while a dog pants when both are taking a long walk in the summer. First, you will create an initial model of this Integrated Phenomenon, which you will revise over the course of the segment.

To understand the phenomenon, you will examine how weather impacts organisms by exploring how the creation and movement of air masses change weather. You will take a closer look at severe weather and its damaging effects and make recommendations for methods and technologies that provide timely forecasts.

Next, you will analyze specialized plant and animal traits that increase the chances of an organism’s survival. In the first Engineering Challenge, you will design a structure that mimics a trait in nature.

You will also create a brochure describing animals’ unique traits.

Last, you will investigate the interactions between body systems and create a model of the human body. In the second Engineering Challenge, you will build a prosthetic hand. You will examine tissues and cells, use tissue samples to find a diagnosis, and find out how the nervous system controls other body systems.

At the end of this segment, what information will you use to explain why a human sweats while a dog pants during hot weather?

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Segments 2

Segment Questions As you go through the lessons in this segment, consider these questions to help explain part of the Integrated Phenomenon.

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Air Pressure and Wind How do differences in air pressure explain wind? How does wind chill impact living things?

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Water and the Weather What happens to the water in sweat once it sits on your skin? What is the water cycle?

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Air Masses and Changing Weather How do air masses relate to changes in the weather? What conditions would lead forecasters to predict sunny skies?

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Severe Weather What causes heat waves? How does humidity impact heat waves? How does this weather impact humans and other living things?

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Traits for Survival What is a trait? What traits help organisms survive extreme temperatures? How could two species have different traits to solve the same problem?

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Traits for Reproduction How do some traits help organisms reproduce? Could surviving for a longer time by staying cool in hot weather end up helping a living thing reproduce?

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Interacting Body Systems What are a few ways the excretory system gets rid of wastes? Do all kinds of organisms have the same basic set of body systems? What is similar between exhalation and sweating?

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Levels of Organization How are cells, tissues, and organs related to body systems? What features of lungs help them work to absorb oxygen from the air and release carbon dioxide waste? How are lungs involved in panting?

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Controlling Body Systems Are sweating and panting voluntary or involuntary? What sense receptors would detect weather conditions? What is the pathway of information that would lead from external weather conditions to a response like sweating or panting?

E a r t h S y s t e m s , We a t h e r , a n d O r g a n i s m s

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Weather

ANCHORING PHENOMENON Severe weather events can lead to extreme loss of life and property.

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Phenomenon-Based Storyline As part the National Oceanic and Atmospheric Administration (NOAA), your task is to develop instruments for measuring atmospheric conditions, interpret weather maps, make weather forecasts, issue severe weather warnings, and create severe weather action plans.

Next Generation Science Standards Performance Expectations MS-ESS2-4.

MS-ESS2-5.

MS-ESS2-6.

MS-ESS3-2.

MS-ETS1-2.

Develop a model to describe the cycling of water through Earth’s systems driven by energy from the sun and the force of gravity.

Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions.

Develop and use a model to describe how unequal heating and rotation of the Earth cause patterns of atmospheric and oceanic circulation that determine regional climates.

Analyze and interpret data on natural hazards to forecast future catastrophic events and inform the development of technologies to mitigate their effects.

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

MS-ETS1-4.

Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering Practices Developing and Using Models • Develop a model to describe unobservable mechanisms. • Develop and use a model to describe phenomena.

• Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Planning and Carrying Out Investigations Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.

Analyzing and Interpreting Data Analyze and interpret data to determine similarities and differences in findings.

Engaging in Argument from Evidence Evaluate competing design solutions based on jointly developed and agreedupon design criteria.

Crosscutting Concepts

Disciplinary Core Ideas

Patterns Graphs, charts, and images can be used to identify patterns in data.

ESS2.C: The Roles of Water in Earth’s Surface Processes • Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land. • Global movements of water and its changes in form are propelled by sunlight and gravity. • The complex patterns of the changes and the movement of water in the atmosphere, determined by winds, landforms, and ocean temperatures and currents, are major determinants of local weather patterns.

Cause and Effect Cause and effect relationships may be used to predict phenomena in natural or designed systems.

Systems and System Models Models can be used to represent systems and their interactions—such as inputs, processes, and outputs—and energy, matter, and information flows within systems.

Energy and Matter Within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter.

Influence of Science, Engineering, and Technology on Society and the Natural World The uses of technologies and limitations on their use are driven by individual or societal needs, desires, and values; by the findings of scientific research; and by differences in such factors as climate, natural resources, and economic conditions. Thus technology use varies from region to region and over time.

ESS2.D: Weather and Climate • Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns. • Because these patterns are so complex, weather can only be predicted probabilistically.

ESS3.B: Natural Hazards Mapping the history of natural hazards in a region, combined with an understanding of related geologic forces can help forecast the locations and likelihoods of future events.

ETS1.B: Developing Possible Solutions • A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. • There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem.

• Models of all kinds are important for testing solutions.

ETS1.C: Optimizing the Design Solution The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

We a t h e r

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LESSON 6

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Air Pressure and Wind You cannot see it but you can feel it—what is wind, and what makes it blow?

Introduction On the day this photo was taken, the tall grasses were waving back and forth and the blades on the wind turbines in the distance were spinning. Of course, you know the cause is wind. But what is wind, and what causes it to blow? Why is wind strong enough to turn huge wind turbine blades one day, when it barely rustles the tall grass on other days?

Air is matter and wind is air in motion. Because air is matter, it has weight and can make objects move. When something is not heavy, people say it is “as light as air”—like the air has no weight at all. But the weight of air can be measured. The atmosphere contains an enormous amount of air and pushes down on the ground with a great force.

You have already learned about temperature, and now you will explore one of the important relationships in weather—between atmospheric pressure and wind. You will learn how atmospheric pressure varies with altitude, how it is measured, and how changes in it cause wind. You will explore how wind interacts with other parts of the Earth system and how it is involved in the flow of energy. You will conclude by finding out how engineers designed hang gliders so that people can soar on the winds.

Vocabulary atmospheric pressure the weight of the air pushing down on an area; the force exerted over an area by all of the air above that area density a property of matter that is equal to the amount of mass in a certain volume of matter sea level the elevation of the land surface where the atmosphere meets the ocean barometer a tool used to measure atmospheric pressure wind air that is moving from a region of higher pressure to a region of lower pressure anemometer a tool used to measure wind speed convection cell a circulation of matter, such as air, caused by constantly rising warm matter and falling cool matter prototype a working model of a design solution that can be used for testing and refining the design

Next Generation Science Standards Performance Expectations MS-ESS2-5. Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions.

MS-ESS2-6. Develop and use a model to describe how unequal heating and rotation of the Earth cause patterns of atmospheric and oceanic circulation that determine regional climates.

MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering Practices Developing and Using Models • Develop and use a model to describe phenomena. • Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Planning and Carrying Out Investigations Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.

Crosscutting Concepts Cause and Effect Cause and effect relationships may be used to predict phenomena in natural or designed systems.

Systems and System Models Models can be used to represent systems and their interactions— such as inputs, processes, and outputs—and energy, matter, and information flows within systems.

Disciplinary Core Ideas ESS2.C. The complex patterns of the changes and the movement of water in the atmosphere, determined by winds, landforms, and ocean temperatures and currents, are major determinants of local weather patterns.

ESS2.D. Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns.

ETS1.B. • A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. • Models of all kinds are important for testing solutions.

ETS1.C. The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

Air Pressure and Wind

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1. Atmospheric Pressure

Although pressure within the tire increases as the tire is pumped up, air pressure outside the tire is also pushing against its outside walls— as well as on you and everything else on Earth.

Air can affect the shape of things. How? A bike tire feels squishy when it goes flat because it does not have enough air in it. You have to pump it full of air to make it firm again. So, how does adding air to a bike tire help it keep its shape?

Pumping air into a bike tire increases the pressure inside the tire.

Pressure is a force applied to a certain area, with force being any push or pull. The girl pushing down on the pump in the photo is exerting a force on the handle of the pump. The particles in the air also push on the inside of the tire when they bump into the sides of the tire tube. As more air is pumped into the tire, more particles bump into the tube sides, increasing the pressure of the air inside the tire.

The pressure of the air inside the tire is not the whole story behind why bike tires need to be filled with air. The air outside of the tire is also pushing against the outside walls of the tire. In fact, all of the air in the atmosphere above the tire is pressing down on the tire. Air may be very light, but there are many kilometers of air above the bike tire as well as above you. Earth’s gravity pulls on all of this air, giving it weight.

Atmospheric pressure is the weight of the air pushing down on an area and is often measured in millibars (mb). It pushes down on you, the bike, the ground under the bike, and everything else on Earth.

Pressure increases as the density of air increases. Density is a property of matter that is equal to the amount of mass in a certain volume of matter. For air, density depends on the number of particles that are in a given volume. You can use the model in Figure 1A to explain this relationship. The model on the left represents air at sea level, while the one on the right represents air at the top of Mount Whitney. Notice that there are more particles in the same volume of air at sea level than on top of the mountain. The models show that air is less dense at higher altitudes than at lower altitudes. As a result, atmospheric pressure is also lower at higher altitudes than at lower altitudes.

The Density of Air Depends on Altitude Sea level, 0 km (0 ft)

Figure 1A These particle models, shown in the circles, compare the density of equal volumes of air at sea level and at the top of Mount Whitney in California.

The air is less dense on the top of the mountain because it contains fewer particles there than at sea level.

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Lesson 6

Top of Mt. Whitney, 4.4 km (14,505 ft)

Troposphere

Altitude (km)

Stratosphere

Air pressure

The density of air in the atmosphere Atmospheric Pressure and Density Decrease with Altitude decreases as altitude increases because 50 gravity pulls air downward. The density of air depends on altitude because gases are highly compressible. That means that air’s volume will shrink when you press 40 on it. In the atmosphere, air presses down on the air below it. Think of a tall stack of pancakes. The pancake on top will be the fluffiest because no other pancakes 30 are pressing down on it. The pancake on the bottom will be a bit squished because the weight of all the other pancakes is pressing down on it. As a result, that 20 bottom pancake will be a little bit denser Mount Everest than the pancakes above it.

San Just like the bottom pancake, the Francisco Mount air at the bottom of the troposphere 10 (sea level) Whitney is compressed by all the air above it.

Therefore, air is more dense at sea level.

Denver 5 Sea level is the elevation of the land surface where the atmosphere meets 0 200 400 600 800 1,000 the ocean. It is the starting point for Pressure (mb) Air density altitude measurements at 0 kilometers (km). Some places on land, such as New Orleans, Louisiana, are a few meters below sea level. Others, such as Figure 1B the top of Mount Whitney, California, are more than a kilometer above There is a cause-and-effect sea level. Therefore, the density of air in New Orleans is greater than relationship between altitude and the density of the air on top of Mount Whitney. atmospheric pressure. The density of Atmospheric pressure decreases as altitude increases. This is because air decreases as altitude increases. the density of air decreases the higher you go. The graph in Figure 1B As the density of air decreases, note shows this. At sea level, such as the shoreline of San Francisco, how the atmospheric pressure also California, the atmospheric pressure is 1,013 mb. In Denver, Colorado, decreases rapidly. at about 1.6 km above sea level, atmospheric pressure is 840 mb. At the top of Mount Whitney, about 4.4 km above sea level, atmospheric pressure is about 600 mb. At 10 km above sea level—the top of the troposphere in some places—atmospheric pressure is only about 260 mb.

Did you notice how much lower the density of air is at 10 km than at sea level? This explains why commercial aircraft cabins must be pressurized.

Thus, there is a cause-and-effect relationship between altitude and atmospheric pressure. A cause-and-effect relationship is a connection between events in which one event is caused by another event. When altitude increases, atmospheric pressure decreases; this relationship can help you predict how atmospheric pressure will vary from place to place in the world.

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2. How Atmospheric Pressure Is Measured

Figure 2 Evangelista Torricelli’s barometer used a mercury-filled tube turned upside down in a dish of mercury to measure atmospheric pressure. As air pressure increases, more force pushes down on the mercury in the dish, causing the mercury to rise in the tube. The height of the mercury in the tube can be measured by the scale. Mercury has since been found to be harmful to handle, so scientists today typically will use aneroid or digital barometers.

Beyond the thermosphere, the density of air is extremely low. There, outer space is considered a vacuum, or empty space. Scientists can make vacuums in containers at sea level, too. How was the first vacuum made?

In 1643, Italian physicist Evangelista Torricelli invented the first human-made vacuum. He removed almost all the air from a container without letting the surrounding air flow back in. Figure 2 shows how he did this. He filled a thin glass tube, sealed at one end, with liquid mercury. Next, he flipped the tube over into a dish of mercury. Some, but not all, of the mercury flowed out of the tube into the dish, leaving an airless space, or vacuum, at the top of the tube.

The weight of the atmosphere pushing down on the mercury in the dish keeps all the mercury from flowing out of the tube. When there is more atmospheric pressure, there is more force pushing on the surface of the mercury in the dish. So, more mercury moves up the tube and reduces the space of the vacuum. Thus, the height of mercury in the tube increases as atmospheric pressure increases and decreases as pressure decreases. Torricelli’s tube of mercury was also the first barometer, a tool that is used to measure atmospheric pressure.

Torricelli observed that the height of the mercury in the tube changed from day to day. Atmospheric pressure at a given location depends on weather, as well as altitude. It is usually higher when air is colder because cold air is denser than hot air. Likewise, pressure is usually lower when air is warmer and therefore less dense.

Scientists today do not use mercury barometers. They mostly use digital barometers to analyze changes in atmospheric pressure to help them forecast the weather. When these changes are measured in conjunction with other factors such as temperature, cloud formation, and wind, scientists can predict approaching weather more accurately.

Measuring Atmospheric Pressure with Mercury Glass tube

Vacuum Scale

Mercury Air pressure

Air pressure

Rising mercury

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Dish of mercury

Differences in Atmospheric Pressure Cause Wind

Cold air

Higher pressure

Warm air

Wind

Figure 3A Wind is moving air that blows from regions of high pressure to those of low pressure. Because dense cold air flows toward less dense warm air, wind also usually blows from colder areas to warmer areas.

Lower pressure

3. Wind Most people do not notice changes in air pressure, especially small ones. But, they certainly notice when a strong wind whips through tree branches. How are wind and air pressure related?

The atmospheric pressures at a given altitude only vary by a relatively small amount. However, small differences in atmospheric pressure from place to place cause wind. Wind is air moving from a region of higher pressure to a region of lower pressure. Look at the model that relates wind to pressure in Figure 3A. The air from the higher pressure area flows to the lower pressure area. Remember, cold air is denser and has a higher pressure than warm air does. So, wind usually blows from colder regions toward warmer ones.

Wind speeds vary from day to day and even throughout the day.

Some days may be very calm, with only a gentle wind rustling tall grass, while other days the wind may be so strong that you feel like you might be blown over. The gentle wind is air that is moving slowly, while the strong winds mean that the air is moving quickly.

Differences in atmospheric pressure cause wind, and increasing the difference in atmospheric pressure causes wind speed to increase.

Thus, a gentle wind is caused by a small difference in pressure, and a higher wind speed is caused by a larger difference in pressure.

Scientists use this cause-and-effect relationship to predict wind speeds so that they can forecast damaging high-speed winds. By determining the pressure differences across a region, they can calculate the expected wind speed.

Wind speed is often measured in units of kilometers per hour (km/h). In the United States, it is traditionally expressed in units of miles per hour (mph). An anemometer is a tool used to measure wind speed. The photo shows one type of anemometer, which has little cups that are pushed by the wind. The faster the cups rotate, the higher the wind speed.

Wind speed increases as the difference in pressure increases.

Anemometers are instruments that measure wind speed. Wind pushes on the cups of this anemometer, making them rotate. The faster the wind speed, the faster the cups move.

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The Beaufort Scale Beaufort Number

Wind Speed (km/h)

0

<1

Smoke rises straight up.

1

1–5

Smoke is blown in the direction wind is going.

2

6–11

Leaves rustle.

You feel wind on your face.

3

12–19

Light flags stretch out.

4

20–28

Dust is blown.

Small branches move.

5

29–38

Small trees sway.

6

39–49

Large branches move.

7

50–61

Large trees move.

8

62–74

Twigs break off trees.

9

75–88

Shingles are blown off buildings.

10

89–102

Trees are uprooted.

11

103–117

12

≥118

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Effect

Widespread damage occurs.

Severe hurricane damage

What effect could higher wind speeds have on the environment around you? The Beaufort Scale, shown in Figure 3B, describes the effect winds of different speeds have on the surroundings. This scale was originally developed in 1805 by Commander Francis Beaufort of the British Navy as a way for sailors to classify the effects of different wind speeds upon a man-of-war sailing ship while out at sea. Today, it also includes the effects of wind on land. For example, according to the Beaufort Scale, leaves will rustle at approximately 6–11 km/h, yet shingles are blown off rooftops when winds reach approximately 75–88 km/h. While this scale is not often used in forecasts anymore, it allows you to use your own observations of wind to estimate wind speed if you do not have an anemometer. You can give it a try by simply looking outside on a windy day.

In addition to its speed, wind is described by the direction from which it is blowing across Earth’s surface. Winds are named after the direction they blow from. For example, a 10 km/h northwesterly wind is blowing from the northwest toward the southeast. That means the wind would be blowing in your face if you are facing the northwest. A 30 km/h easterly wind is blowing from the east toward the west three times as fast as a 10 km/h wind.

Now when you hear that a 10 km/h northwesterly wind is forecast, you know more about the weather than just the wind speed and direction. You also know that the atmospheric pressure is higher and the temperature is colder in the northwest than in the southeast because winds blow from high pressure to low pressure. And, according to the Beaufort Scale, if you hear instead that an 89 km/h wind is forecast, you know it is a good idea to stay inside if you can!

Figure 3B Wind is described by its speed and the direction from which it is blowing. The Beaufort Scale classifies wind speeds based on their effects on the surroundings. This 200-year-old scale allows you to estimate wind speed without the use of an anemometer by using observation of your surroundings instead.

4. Wind in the Earth System The Beaufort Scale is a historic scale that is not often used today. However, it is based, in part, on the effect of wind’s force upon things. How else does wind affect parts of the Earth system?

Wind interacting with the biosphere is seen in animals using wind for transportation and wind spreading plant seeds and pollen. Gliding birds, such as albatrosses, depend on winds above the water to glide and soar long distances over the ocean without flapping their wings. The dandelion seed is attached to a bit of fluff, which wind carries away from the parent plant to a new place to grow. This fluff floats on the slightest of breezes, as shown in the photo.

Winds can also affect living things by making them feel cooler. Wind chill describes how much colder the temperature feels because of wind moving over your uncovered skin. Thermal energy transfers from your body to the air around your skin, and this air is replaced by cooler air when the wind is blowing. Because your skin is constantly transferring thermal energy to cool air, your skin temperature decreases and the air temperature feels cooler to you than it actually is. Wind chill increases as wind speed increases because higher speed winds replace air around you faster and make temperatures feel cooler.

Strong winds can be dangerous on a cold day because your skin can freeze quickly.

Wind interacts with the geosphere and hydrosphere by moving materials, making waves, and increasing evaporation. It blows parts of the geosphere, such as sand and soil, from place to place.

As the wind blows materials over land, it erodes rocks, hills, and mountains. As the wind blows over the ocean and other bodies of water, it transfers energy to the water and makes waves. High-speed winds can result in large waves, and it also increases how quickly water evaporates into the atmosphere.

Wind occurs in the atmosphere but affects the biosphere, geosphere, and hydrosphere in various ways. Birds use wind to glide, and winds spread the seeds of plants.

Wind makes the air feel colder to the skin. Wind also moves sand, soil, and rocks, causes waves, and hastens evaporation.

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A Convection Cell in the Atmosphere

5. Convection Cells

Moving sand and creating ocean waves are examples of the d Win effects of wind transferring energy between the atmosphere and other parts of the Earth system.

But where does wind get that Cooled air is more Convection cell Warmed air is less dense so it sinks. dense so it rises. energy from?

The sun is the original source of the wind’s energy. Without d the sun, there would be no Win difference in temperature, and thus, no difference in pressure. ce urfa Winds occur because different s rm Wa parts of Earth’s surface are heated unequally by sunlight. Cooler land ce a f r and water cool the air above them, l su Coo causing a region of higher pressure to form. Warmer parts of the land so es ion. s a t e and bodies of water warm the air ecr rec e d this di r u above them, causing a region of ss n pre ows i r i lower pressure to form. Air flows A ir fl a from the regions of high pressure to the regions of low pressure.

Areas of high and low pressure are connected by a circular pattern of Figure 5 air flow. A convection cell is a circulation of matter, such as air, caused A cycle of rising warm air and falling by constantly rising warm matter and falling cold matter. Examine the cold air forms a circulation of air in the movement of warm and cold air in the model of a convection cell in atmosphere called a convection cell.

Figure 5. Notice that the circle is perpendicular to Earth’s surface. The Wind is the horizontal flow of air in a air moves in this circle because cold air is denser than warm air. The convection cell. The uneven heating warm air over hotter surfaces rises because it is less dense than the of Earth by the sun causes convection surrounding air. At higher altitudes, the warm air cools and becomes cells by producing areas of high and denser. The rising air creates an area of high pressure at high altitudes. low pressure.

Eventually, the air becomes dense enough to sink down to the surface.

At high altitudes, the pressure is low where the air is sinking and the air flows horizontally from high- to low-pressure areas. At the surface, the cooler, denser air flows in to take the place of the rising air. You already know about this horizontal flow of air—it is wind.

Some convection cells on Earth are very large, and others are smaller. Large, global convection cells transfer energy from the warm equator to the cooler, higher latitudes. These convection cells lead to global wind patterns. Smaller convection cells also transfer energy daily in the atmosphere where large bodies of water meet the land.

That is why the weather at the beach may be very windy in the afternoon when the air has heated up inland.

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Key Science Concept

Sea and Land Breezes These models show the convection cells where land and large bodies of water meet. Remember, water changes temperature more slowly than land. Even though the land and nearby water receive the same amount of sunlight, the land warms up more quickly than water during the day and the water cools off more slowly at night. The resulting wind patterns are called sea breezes and land breezes.

Sea Breeze Warm rising air

Higher pressure air

Lower pressure air

Wind direction Cooled sinking air

Land is warmer

Sea is cooler

Land Breeze Warm rising air

Higher pressure air

Lower pressure air

Wind direction Cooled sinking air

Land is cooler

Sea is warmer

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Engineering Design

Otto Lilienthal was known as the “Flying Man” of Germany. He is shown here testing one of his gliders.

He created multiple prototypes for his glider designs and tested them carefully. He upheld the idea that researchers should jump before they fly, suggesting they should work their way up to increasingly powerful gliders based on initial, modest successes.

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6. Designing Hang Gliders to Ride the Wind Birds are not the only living things that can glide on air. Humans have also learned how to use wind to soar at great heights above Earth.

However, they need to use technology to do it. How did engineers develop a safe design for hang gliders?

Hang gliders are different from airplanes—they do not have motors.

Yet, like airplanes, they are heavier than air and are pulled to the ground. To launch hang gliders, pilots usually jump off the edge of a cliff and ride winds that blow up a hillside.

In 1891, German engineer Otto Lilienthal designed the first glider by applying his studies of the physics of bird flight. He drew detailed models of his designs, and then he made a prototype. A prototype is a working model of a design solution that can be used for testing and refining the design. He also built a hill to test his prototype.

After testing a design, Lilienthal modified it to try to improve it.

For example, he made the wings shorter so that the glider could hold up against stronger winds. He would continue to test and improve his designs over and over again based on his test results. In an effort to maximize the flight time, he tested more than 16 different glider designs in this way. His longest flight was a short 15 seconds. His research came to an end in 1896, when he died in a fatal crash caused by a gust of wind. The crash revealed one of the limitations of his glider designs—it was difficult to control.

Jet planes were flying across the skies before the next major advance in hang glider design. In the late 1940s, engineer Francis Rogallo designed a large flexible wing that resembled a kite, which became known as the Rogallo wing. Although the wing had an advantage over Lilienthal’s designs in that it could be easily steered, the kite-like wing was not the end in improvements in hang glider design. Most modern hang gliders now include an A-shaped frame under the wing to support the pilot and an easy way to steer the glider. To improve the design of hang gliders, engineers need to understand winds in the atmosphere. For each improvement in glider design, engineers follow an iterative process, following a cycle of testing, modifying, retesting, and modifying again until the optimum design is reached.

Hang glider safety has improved since Lilienthal’s time and continues to improve with newer designs and modifications. However, hang gliding is a dangerous sport and is not something to attempt without proper training. Pilots need months of training before gliding through the air. It is important for pilots to have a thorough understanding of wind and weather conditions before they fly.

Engineers have made many improvements to hang gliders since the first hang gliders of Lilienthal’s time. However, pilots of hang gliders must continue to understand winds and be well-trained to glide safely.

LESSON SUMMARY

Air Pressure and Wind Atmospheric Pressure Atmospheric pressure is the weight of air pressing down on a certain area.

Pressure increases as the density of air increases. Thus, air is more dense and atmospheric pressure is higher at lower altitudes than at higher altitudes.

How Atmospheric Pressure Is Measured Evangelista Torricelli invented the mercury barometer.

In this type of barometer, the height of mercury in a glass tube increases as atmospheric pressure increases. Atmospheric pressure changes in a given place are related to changes in the weather.

Wind Wind is air that flows from areas of high pressure to areas of low pressure. Wind speed is measured with an anemometer and increases as the difference in pressure increases. Descriptions of wind also include the direction from which the wind is blowing.

Wind in the Earth System Wind in the atmosphere interacts with the biosphere, geosphere, and hydrosphere. It transports seeds and is used by birds to glide. It also causes wind chill, erodes rocks, moves soil, produces waves, and contributes to evaporation.

Convection Cells Convection cells are circular air patterns that are formed by constantly rising warm air and sinking cooled air. They are driven by the uneven heating of Earth by energy from the sun.

Designing Hang Gliders to Ride the Wind The design of hang gliders has been improved by many engineers over decades. For each improvement, engineers followed an iterative or continual process.

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LESSON 7

82

Water and the Weather How does water affect weather as it cycles through the Earth system?

Vocabulary groundwater water located underground that fills pore spaces in soil and rock layers water cycle the movement of water through the Earth system transpiration the evaporation of water from the leaves of plants

Introduction In the photo, the tallest of the distant snow-capped peaks is hidden by dark, threatening clouds. However, the misty valley and its rushing stream are lit up by beams of sunlight. In this setting, how does water move from snow to the stream to the clouds? Where is water changing from a liquid to a gas or to a solid? Which processes require gravity?

Water continuously cycles through the Earth system, changing its location and its state. The snow on a mountain may melt and flow down to the stream. Water in the clouds may fall as rain and snow, while water in the stream evaporates into the atmosphere. Trillions upon trillions of water particles evaporate from Earth’s surface every second. And, nearly all the energy needed for this cycling of water comes from the sun—Earth’s ultimate energy source! As water makes its journey through the water cycle and changes state, it transfers energy to and from the surrounding environment.

You may not be able to see all the processes by which water moves between different parts of the Earth system. But in this lesson, you will use models of the water cycle to help you understand these mechanisms and how they affect weather. You will learn the details about how water enters and leaves the atmosphere. You will also explore how the water cycle affects the characteristics of the atmosphere. Finally, you will learn how engineers choose designs for systems to clean wastewater in a town.

absolute humidity the amount of water vapor in a given volume of air, usually expressed as grams per cubic meter (g/m3) relative humidity the ratio, usually expressed as a percentage, of the actual amount of water vapor in air to the maximum amount of water vapor air can hold at the same temperature dew water droplets that form on surfaces due to condensation of water vapor dew point the temperature at which air is saturated with water vapor crystallization the formation of a solid structure whose atoms or molecules are arranged in a repeating, three-dimensional pattern precipitation solid or liquid water that falls from clouds to the ground

Next Generation Science Standards Performance Expectations MS-ESS2-4. Develop a model to describe the cycling of water through Earth’s systems driven by energy from the sun and the force of gravity.

MS-ETS1-2. Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

Science and Engineering Practices Developing and Using Models Develop a model to describe unobservable mechanisms.

Engaging in Argument from Evidence Evaluate competing design solutions based on jointly developed and agreed-upon design criteria.

Crosscutting Concepts Energy and Matter Within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter.

Disciplinary Core Ideas ESS2.C. • Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land. • Global movements of water and its changes in form are propelled by sunlight and gravity.

ETS1.B. There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem.

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1. Sun, Gravity, and the Water Cycle

Figure 1 The water cycle is the movement of water through the Earth system. It is driven by energy from the sun and by the pull of gravity. During the water cycle, water moving through bodies of water, the ground, and the atmosphere continuously cycles through the parts of the Earth system.

You sweat when you exercise, but the water particles in sweat do not usually just stay on your skin. As they dry, they evaporate into the air, and days later, those same water particles may fall on someone else as rain. Where is water found in the Earth system?

The hydrosphere is unevenly distributed on Earth. About 97 percent of Earth’s water is found in the ocean. The atmosphere contains only 0.001 percent of the total water on Earth. Water is also found in other places, including ice, freshwater (water that is not salty), living things, and the ground. Groundwater is water located underground that fills pore spaces in soil and rock layers.

The water cycle is the movement of water through the Earth system.

It is driven by the energy from the sun and by gravity. Figure 1 models this cycle, including mechanisms that you cannot directly observe, such as evaporation. Water in the atmosphere, above ground, in groundwater, and in living things are all part of the water cycle.

Energy from the sun drives evaporation, causing liquid water at Earth’s surface to change to water vapor that enters the atmosphere.

Plants also give off water vapor through their leaves as they use energy from the sun to grow. Once in the atmosphere, water vapor may change back into liquid water from condensation.

Gravity causes the downward movement of water and pulls larger water droplets and ice crystals toward the ground as raindrops, snowflakes, or small icy balls of hail or sleet. During infiltration, water seeps into the ground. Gravity also causes water to flow downhill over the surface as runoff. Runoff and groundwater feed streams, rivers, lakes, and the ocean, and the sun provides energy for water to evaporate from any of these places into the atmosphere again.

A Model of the Water Cycle Condensation Precipitation

Solar energy

Runoff Infiltration Groundwater flow

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Evaporation

2. Evaporation and Transpiration Spring rains fill the lake at the park. However, during a dry summer, you notice that its water level keeps getting lower and lower, and the ground around it dries out. Where did the lake’s water go?

Most water vapor in the atmosphere comes from evaporation of liquid water at the enormous surfaces of Earth’s oceans. Water in lakes, rivers, and the surface of the soil also evaporates. What happens during evaporation? Remember, water changes state from a liquid to a gas when it evaporates. Water particles in liquid water are always moving and bumping into each other, and some of these particles have more kinetic energy than others. At the surface of liquid water, some particles have enough kinetic energy to escape the liquid and become water vapor.

Water also enters the atmosphere through transpiration, which is the evaporation of water from the leaves of plants. The water in the leaves comes from the soil as plant roots absorb groundwater and the water travels up the stem of the plant to its leaves. Similar to the pores in your skin that allow you to sweat, plants have tiny openings on the underside of their leaves. Water vapor escapes through these pores back into the atmosphere. Thus, groundwater enters the atmosphere through plant transpiration.

Evaporation and transpiration occur more quickly on a hot day.

Water evaporates faster at high temperatures because more water particles have enough energy to escape the liquid surface or leaf.

Figure 2 shows this movement. The kinetic energy of moving water particles ultimately comes from energy from the sun. So, energy from the sun that is absorbed by water and plants drives evaporation and transpiration in the water cycle.

Figure 2 Most water enters the atmosphere by evaporation of water at Earth’s surface. Water also evaporates from plants through their leaves by transpiration. Energy from the sun drives these processes.

Evaporation and Transpiration in the Water Cycle evaporation a nd tra n

Transpiration s

Particle enters gas phase

Liquid particle gains energy

n tio ra

Mi cr

p ic co

w of vie

pi

os

Evaporation

Gas Liquid

Lake

Soil

Ocean

Liquid particles collide

Leaf

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3. Humidity

Places such as the Everglades near Miami, Florida (top photo), are described as humid because they have a high absolute humidity. Phoenix, Arizona, in the Sonoran Desert (bottom photo), is considered dry. Relative humidity is the ratio of the amount of water in the air to the amount of water in saturated air.

Even when the temperatures in the Everglades near Miami and Phoenix in the Sonoran Desert are the same, the air may feel very different. The air often feels stickier in Miami than in Phoenix. Why? Differences in the amount of water vapor in the atmosphere affect the way the air feels. Humidity is the general term used to describe the amount of water vapor in the atmosphere at a given time and place.

Absolute humidity is the amount of water vapor in a given volume of air, usually expressed as grams per cubic meter (g/m3). A higher absolute humidity means there is more water vapor in the air. For example, the air in Miami often contains more water vapor than the air in Phoenix. Therefore, the absolute humidity is higher in Miami and the air feels muggy. The air in Phoenix feels very dry because the absolute humidity is low. You can see the difference absolute humidity makes in these two locations by comparing the photos.

The amount of water vapor that air can hold depends on its temperature. Just like when a sponge is sopping and cannot hold any more liquid, air is saturated when it cannot hold any more water.

Relative humidity is the ratio of the actual amount of water vapor in the air (absolute humidity) to the maximum amount of water vapor that the air can hold at the same temperature. Figure 3 shows how temperature affects the amount of water vapor that air can hold before saturation. The amount of water vapor that air can hold increases as the temperature increases. When weather reports refer to humidity, values of relative humidity are expressed as a percentage. This formula shows how to calculate the relative humidity in a specific volume: relative humidity (%) =

amount of water vapor in air × 100 amount of water vapor the air can hold

So, for example, the relative humidity in Miami might be 75 percent while the relative humidity in Phoenix might be 16 percent.

The Amount of Water Vapor in Air Versus Temperature

Figure 3 The amount of water vapor that air can hold increases as temperature increases. The blue line represents the maximum amount of water vapor the air can hold at a given temperature.

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Absolute Humidity (amount of water vapor (g/m3)

50 40

Air is saturated, Relative humidity = 100%

30 20

Relative humidity is less than 100%

10 0 −20

−10

0

10

20

Temperature (°C)

30

40

50

4. Dew and Condensation You walk through the grass on a cool morning. Even though it hasn’t rained and the grass was not watered by sprinklers, your shoes are all wet. Why is the grass wet in the morning?

Grass may be wet in the morning because it is covered with water droplets that formed at night. Dew is water droplets that form on surfaces due to condensation of water vapor.

Condensation is the opposite change of state of evaporation. Water particles in water vapor come together to form drops of liquid water during condensation. Just as evaporation occurred when water absorbed energy, water releases energy during condensation.

Dew forms at the dew point, which is the temperature at which air is saturated with water vapor. The dew point depends on the amount of water vapor in the air, so it can vary. The dew point is higher when the amount of water vapor is greater, and lower when the air is drier. At the dew point, air is saturated, so liquid water condenses out of the air. Another way to say this is that relative humidity is 100 percent at the dew point.

Dew forms as the air cools at night. As the temperature decreases, the amount of water vapor that the air can hold also decreases.

Consider a day when the dew point is 20°C. Dew does not form during the day when the temperature is greater than 20°C. During the night, the air cools to 20°C and the relative humidity reaches 100 percent. Water condenses out of the air onto blades of grass, as well as other surfaces, as liquid droplets—dew. Think about walking through dew-covered grass early in the morning. As the sun warms up the air during the morning, air can hold more water. So, the dew evaporates and becomes water vapor again, and you can walk through the grass without getting your shoes wet!

When the dew point is below 0°C, tiny ice crystals form instead of liquid water. Frost is a thin layer of ice crystals that forms on surfaces, such as grass. Frost forms at the frost point, which is the dew point when the temperature is below freezing or 0°C. Fog is water droplets that are suspended in the air near the ground.

It forms when the temperature drops below the dew point. Instead of forming dew on cool surfaces, droplets of water form in the air, making a cloud near the ground like the one in the photo at the beginning of this lesson.

Tiny water droplets, called dew, form when water vapor in the air condenses at the dew point. The dew point is the temperature at which air is saturated with water. Dew forms at night when the air temperature cools to the dew point.

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Cloud Formation in the Water Cycle

Decreasing temperature

Condensed moisture in air

Cooling, moist air

Warm, moist air

Figure 5A Clouds are made of water droplets or ice crystals. Water droplets form around dust, salt, or smoke particles as moist air rises and cools to the dew point, causing water vapor to condense. Clouds are an important part of the water cycle as water changes state when clouds form and clouds transport water back to Earth’s surface.

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5. Clouds Even on a humid day, you cannot see the tiny particles of water vapor in the air around you, but you can see clouds in the sky. They may be the wispy Dew point: 16°C clouds that appear on pleasant days Air temperature: 16°C and look like they were painted with a stroke of a paintbrush. Or they may look like puffy cotton balls or a thick, gray ceiling during storms. How do clouds form and why are they different?

A cloud is a collection of liquid water droplets or solid ice crystals that Dew point: 16°C you can see. The water droplets or ice Air temperature: 24°C crystals in clouds are so tiny that they can stay in air. Gravity pulls downward on the tiny particles, but updrafts, or air that is flowing upwards, push up the particles. Gravity is not strong enough to overcome this upward push, so the water droplets and ice crystals in clouds Dew point: 16°C Air temperature: 33°C float.

Liquid droplets that make up clouds form in a way similar to the way dew forms, in which moist air must reach the dew point. Remember that warm air cools as it rises. Look at what happens to the air in Figure 5A. The higher the air rises, the more it cools. When the air reaches a height where its temperature is the same as the dew point, water vapor can condense. However, water vapor needs a surface on which water particles can form droplets. In the atmosphere, droplets form around tiny particles of dust, salt, or smoke. Many, many water droplets must form to make a cloud.

Clouds that are made of ice crystals form in a slightly different way. These clouds form when the temperature is below freezing and water vapor forms crystals. Crystallization is the formation of solid structures, called crystals, whose atoms or molecules are arranged in a repeating, three-dimensional pattern. Water vapor crystallizes around the surface of dust particles or other ice crystals. Snowflakes form in clouds in this way. Some clouds are made of only water droplets or only ice crystals, and some are a mixture of the two.

Clouds are a part of the water cycle, even when rain or snow is not falling from them. Clouds transport water from one area to another, and the water they contain is eventually pulled to the ground again by gravity.

The Mid Clouds Altostratus, altocumulus, and nimbostratus clouds are found at mid-range heights between high and low clouds. Altostratus clouds form a thin gray blanket across the sky, and altocumulus clouds look like they are made of grayish-white puffs of cotton. Altocumulus clouds may indicate that a thunderstorm will occur later in the day. Nimbostratus clouds are dense, dark gray clouds that often bring steady rain or snow.

8,000 m Cirrocumulus

High (Cirrus)

The High Clouds The highest clouds in the sky are made of ice crystals and are usually white.

Cirrocumulus clouds look like light puffs of cotton.

Cirrus clouds are white, wispy clouds. Cirrostratus clouds look like a thin white sheet that covers the sky.

You may see any of the high clouds when the weather is fair, but cirrostratus clouds may mean that rain or snow is on its way.

Types of Clouds

Altostratus

The Low Clouds Cumulus, stratocumulus, stratus, and cumulonimbus form at the lowest altitudes.

Cumulus clouds look like big clusters of puffs, and stratocumulus clouds look like rolls of gray bunches bringing snow or rain. Stratus clouds appear like a low, gray ceiling over the sky and may produce light rain. Fog is a stratus cloud at ground level. Cumulonimbus clouds are very tall in height with a top flattened in the shape of an anvil. These dark clouds often bring thunderstorms, hail, and heavy rain.

4,000 m Altocumulus

Nimbostratus 2,000 m Cumulus

Low (Stratus)

Figure 5B Clouds are divided into high, mid, and low clouds based on their altitude in the atmosphere. They are also described by their shapes or if they often bring rain. Knowing the different types of clouds can help you predict the weather.

Cirrus

Cirrostratus

6,000 m

Mid (Alto)

Figure 5B shows various types of clouds. Clouds are divided into three main groups based on their altitude in the sky—high, mid, and low. Each cloud group has members that have different shapes, including wispy, puffy, and sheet-like clouds.

Stratocumulus

Cumulonimbus

Stratus

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6. Precipitation

Rain, snow, sleet, and hail are types of precipitation. While rain is liquid water, the other three types are ice. They are all an important part of the water cycle, as they are the means in which water in clouds reaches the ground.

Big gray clouds appear on the horizon, and the rumble of thunder gets louder and louder. You run inside to avoid the storm coming your way. And just in time! Tiny balls of ice smack into the windows and bounce off the sidewalk. Where did these balls of ice come from?

The icy balls are hail. Like raindrops, they fall from clouds because gravity pulls on them. Precipitation is liquid or solid water that falls from clouds to the ground. It is the main way that water in the atmos­ phere makes its way back to Earth’s surface.

Rain, snow, sleet, and hail are four common types of precipitation and are shown in the photos. Rain is drops of liquid water falling to the ground. Snow, hail, and sleet are solid precipitation. Snow is made of delicate six-sided ice crystals, while hail and sleet are larger ice particles.

How can you tell the difference between sleet and hail? First, the icy balls of hail are bigger than the ice pellets in sleet. Sometimes they are much bigger, getting up to the size of ping-pong balls or even softballs, which is why hail can damage plants, cars, and buildings. Second, sleet and hail fall during different types of storms. Sleet may fall during a storm when the air near the ground is cold, whereas hail may fall during a severe thunderstorm on a warm summer day.

Rain

Snow

Sleet

Hail

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Falling droplet

Before raindrops, snowflakes, or How a Raindrop Grows hail fall from clouds, they must become heavy enough for gravity to overcome Cloud droplet the updrafts that are holding them aloft.

Figure 6 represents one model of how a Collisions raindrop forms and grows in clouds. First, water droplets collide and stick together to form a small raindrop. This raindrop Small raindrop begins to fall through the cloud, growing into a large raindrop as it takes in smaller Growth droplets below it. Notice the raindrop is not the shape of a teardrop. Instead, it has a flat bottom as it grows because air is pushing up on it as it falls. If the raindrop grows large Large raindrop enough, it will break apart into two smaller Growth raindrops. In cold clouds with enough moisture, ice crystals continue to grow and group together in a similar way to form snowflakes that fall toward the ground.

Raindrop divides Hailstones form when air blows tiny ice particles upward and downward many times through clouds and the particles continually grow into bigger balls of ice.

The ice is pushed up by strong updrafts, Two raindrops so hail can grow larger than raindrops or snowflakes before it is pulled to the ground by gravity.

Figure 6 The type of precipitation that reaches the ground depends on the A raindrop grows as small droplets temperatures of the atmosphere. Snowflakes will reach the ground if of water in a cloud collide. When the they fall through air below the freezing temperature of water. But, they raindrop is massive enough for gravity melt and become rain if they fall through warmer air. Rain may also to pull it to the ground, it falls through freeze into sleet if the temperatures near the ground are below freezing. the cloud. It grows even more as it In this case, sleet reaches the ground. falls into the drops below it, and may Rain is measured using a rain gauge, which is a clear container that become big enough to divide into two has an opening at the top so that rain can be collected as it falls. The raindrops. gauge also has a scale on the side that is in units such as millimeters (or inches in the United States) to measure the height of precipitation that is collected. Snow sits on top of the ground, so its depth can be measured with a meter stick.

Precipitation is an important part of the water cycle. It provides freshwater for infiltration that many plants and animals use. Even snow provides freshwater as it melts to form streams that flow into lakes and rivers. Long periods without enough precipitation can lead to droughts. Too much precipitation can also be destructive, causing floods, landslides, and avalanches.

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Key Science Concept

Energy and the Water Cycle This model of the water cycle shows how water on Earth is constantly moving, changing state, and transferring energy between the land, bodies of water, and the atmosphere, by using energy from the sun. The particles of water on Earth complete this cycle eventually: spending time in the ocean, evaporating to become water vapor in the atmosphere, and condensing to form precipitation.

Energy from the sun Condensation

Condensation

Transpiration

Living things

Evaporation

Ocean

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Precipitation

Clouds

Rain

Wind

Sleet

Water storage in the atmosphere

Hail

Snow

Glacier

Frost

Humidity Fog Lake

Dew River

Infiltration

Runoff

Groundwater Groundwater flow

Which states of water become the weather that we experience? Notice that the atmosphere contains water in all three states. Invisible water vapor is stored in the atmosphere as humidity. Liquid water is stored in fog and clouds. Solid water, ice, is stored in certain high-altitude clouds.

Eventually, liquid and solid water fall back to Earth due to the force of gravity, to run over or underground before returning to the ocean.

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Engineering Design

The Arcata Marsh in California is an example of a constructed wetland. A constructed wetland is an engineered wastewater system that cleans water the way a natural wetland does, using plants, microorganisms, and soil.

Constructed wetlands can be used for many applications, from private homes to whole towns.

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7. Engineering Design: Cleaning Wastewater with Plants Every time you shower, wash your hands, or flush the toilet, water goes down the drain. This wastewater is part of the water cycle and eventually makes its way to lakes, rivers, and the ocean. It must be cleaned so it is safe before it enters the environment. Suppose you are an engineer helping to plan a new town. How would you choose the design that is best for treating wastewater produced by this town?

In this situation, there are two possible designs—a constructed wetland, such as the one in the photo, and a typical wastewater treatment facility. A constructed wetland is an engineered wastewater treatment system that uses plants, microorganisms, and soil to clean water as a natural wetland, such as a marsh, would. A typical wastewater treatment plant uses a series of pipes, screens, settling tanks, and filters to move wastewater through the plant. Each step purifies the water a little more until it is cleaned.

Engineers systematically compare competing designs. For a new product, they might test designs under the same conditions to see which is better. For a design that is used onsite at a location such as a wastewater treatment system, they might compare data about how well the design performs. They evaluate possible design solutions based on the criteria and constraints, or the limitations of the possible engineering design.

You need to evaluate the two designs using the criteria and constraints for the town’s system. The criteria state that it needs to serve a certain number of people. It must remove large and small solid particles from the water. It must kill bacteria and other microorganisms that cause disease. Your town plan also requires an animal habitat and outdoor spaces for people to enjoy. One constraint is the cost of the water treatment system. Although you have a lot of land to use, you need to keep the cost low.

Both designs can serve the population and meet almost all the criteria, however, the constructed wetland provides an animal habitat and outdoor spaces. It also costs less than a typical system, which is important. Based on careful consideration of the competing solutions, which design would you choose to clean the town’s wastewater?

This wastewater treatment system design cleans water using a series of pipes, pumps, tanks, and filters. Wastewater systems must be evaluated based on the criteria and constraints of the design.

LESSON SUMMARY

Water and the Weather Sun, Gravity, and the Water Cycle Water is constantly moving through the Earth system. The water cycle is driven by energy from the sun and gravity. Water changes state throughout the cycle.

Evaporation and Transpiration Powered by energy from the sun, water vapor enters the atmosphere mainly through the processes of evaporation of liquid water in bodies of water and the ground, and in transpiration of water from plants.

Humidity Humidity is the amount of water vapor in the air. Relative humidity is the ratio of the amount of water vapor in the air to the amount of water vapor the air can hold at a given temperature.

Relative humidity depends on temperature because warmer air can hold more water vapor.

Dew and Condensation Air becomes saturated with water vapor at the temperature called the dew point. Water vapor condenses to form water droplets on surfaces below the dew point.

Clouds Clouds form when moist air rises and cools to the dew point, allowing water droplets or ice crystals to form. Clouds are classified by their height in the sky, their shape, and if they bring rain.

Precipitation Precipitation is any liquid or solid water that falls from clouds and is pulled to the ground by gravity. It includes rain, snow, hail, and sleet.

Engineering Design: Cleaning Wastewater with Plants In designing a wastewater treatment system, engineers evaluate possible designs based on criteria and constraints.

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Air Masses and Changing Weather

air mass a huge volume of air that has a uniform temperature and humidity at a given altitude weather front the boundary where two air masses meet cold front a weather front in which a cold air mass advances to replace a warm air mass

How do giant masses of air that move around the world change weather?

warm front a weather front in which a warm air mass advances to replace a cold air mass

Introduction You’ve just left home with your umbrella and are headed for the bus stop. There is a light rain with some wind, but you see the sky to the west is bright. What will the weather be like for the rest of the day?

Will the rain get worse? Or will it become clear and calm?

Throughout history, people have studied nature carefully and have identified cause-and-effect relationships in the patterns they observe that help them predict the weather. For instance, thick dark clouds may indicate rain is coming, and wind speed often increases with a greater difference in temperature.

But how do modern scientists use these cause-and-effect relationships to understand the weather? In what ways does investigating moving air masses help explain changes in weather? Scientists also use these relationships to analyze weather data from all over the world to make detailed weather forecasts. The resulting forecast includes the five elements of weather you already know about—wind, temperature, humidity, pressure, and precipitation—and answers many everyday weather questions you might ask. However, they also need to understand the models of air masses, fronts, and pressure systems that form the basis for making these forecasts.

In this lesson, you will learn how elements of weather relate to huge volumes of air called air masses. By the end of this lesson, you will understand how scientists use these relationships along with weather stations and radar to predict your local weather.

stationary front a boundary between a cold air mass and a warm air mass that is not moving occluded front a boundary between one warm air mass and two cold air masses, in which the warm air mass is pushed above the two cold air masses low pressure system an area within the atmosphere where air is rising and winds blow toward the center high pressure system an area within the atmosphere where air is sinking and winds blow away from the center isobar a line on a weather map that connects places that have the same air pressure

Next Generation Science Standards Performance Expectations MS-ESS2-5. Collect data to provide evidence for how the motions and complex interactions of air masses results in changes in weather conditions.

Science and Engineering Practices Planning and Carrying Out Investigations Collect data to produce data to serve as the basis

for evidence to answer scientific questions or test design solutions under a range of conditions.

Crosscutting Concepts Cause and Effect Cause and effect relationships may be used to predict phenomena in natural or designed systems.

Disciplinary Core Ideas ESS2.C. The complex patterns of the changes and the movement of water in the atmosphere, determined by winds, landforms, and ocean temperatures and currents, are major determinants of local weather patterns.

ESS2.D. Because these patterns are so complex, weather can only be predicted probabilistically.

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1. Air Masses

Figure 1 An air mass is a large volume of air that has uniform temperature and humidity.

Air masses may be cold or warm and dry or moist, depending on where they form. Meteorologists use mP, cP, mT, and cT to describe how air masses form because these abbreviations are short and fit easily on maps.

It is a warm, pleasant morning as you head out the door for soccer practice. By break time, you see gray clouds gathering and trees being whipped by winds. By the time you leave practice, rain is pouring down and it is cold. How can understanding air masses explain a sudden change in the weather?

An air mass is a huge volume of air that has a uniform temperature and humidity at a given altitude. Air masses may be warm or cold and moist or dry. They may be thousands of kilometers wide, reaching to the top of the troposphere! As the wind pushes them around the atmosphere, air masses bring their weather characteristics with them as they travel from place to place. Thus, the varying characteristics of air masses bring changing weather.

Air masses form when air stays over an area of land or water for a long time. The properties of the land or water determine their temperature and humidity. Air masses that form over the ocean tend to be moist because they absorb a large amount of water evaporating from the ocean. Air masses that form over land tend to be drier.

Scientists can predict where cold and warm air masses will form by using what they know about the variation of temperature with latitude.

Cold air masses form at high latitudes, where the land and water are colder. Warm air masses form closer to the equator, where the land and water are warmer. Notice where each of the warm, cold, dry, and moist air masses form in Figure 1. The map shows the cause-and-effect relationship between air masses and the places where they form. According to Figure 1, what kind of air mass might be typical for the region where you live? What properties of local land or water cause this?

Air Masses of North America

Maritime (m)— forms over water and is wet

cP

Continental (c)— forms over land and is dry Tropical (T)— forms over the tropics and is warm Polar (P)— forms over polar regions and is cold

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mP

mP

cT mT

mT

Pacific O

cean

cean

tic O

Atlan

Classifying Air Masses Did you notice that each air mass in Figure 1 was labeled with two letters—a combination of “m” or “c” and “P” or “T”? These letters are shorthand notation that represents the moisture and temperature characteristics of air masses and helps to classify them. Each letter gives you information about where the air mass formed and also tells you the properties of the air mass. The letter “m” stands for “maritime,” which means the air mass formed over bodies of water, such as oceans, and is moist. The letter “c” stands for “continental”— the air mass formed over land and is dry. The “P” stands for “polar,” and represents a cold air mass. The letter “T” stands for “tropical,” and denotes a warm air mass. These characteristics are used to describe four common types of air masses that affect the United States: mP, mT, cP, and cT. Moving Air Masses If air masses stayed where they formed, the weather would not be very interesting. Instead, they move from areas of high pressure to areas of low pressure. Moving air masses around the globe bring changing temperature and moisture conditions.

The photos show the type of weather that different air masses are associated with and can bring to locations they travel to. A moist, cool mP air mass forms in the northern Pacific Ocean. This air mass brings cool rainy weather to Seattle and other cities in the Pacific Northwest when it moves onshore. A dry, cold, cP air mass that forms in Canada can bring frigid but fair weather to cities in the Midwest, such as Minneapolis, in the winter. When the moist, warm mT air mass that forms in the tropical parts of the Pacific Ocean travels to coastal regions of southern California, such as the city of San Diego, it brings warm, humid weather.

Seattle mP

Minneapolis cP

San Diego mT

A location’s weather depends on the air mass over it.

When they move, air masses change the weather in their path. They are classified based on where they are from using the letters m, c, P, and T. A i r M a s s e s a n d C h a n g i n g We a t h e r

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2. Weather Fronts

Figure 2A A weather front develops along the boundary where two air masses meet.

A cold front forms where a dense, cold air mass pushes under a less dense, warm air mass. A warm front forms where a warm air mass slides over a cold air mass that is being pushed ahead by the warmer air.

On the soccer field, you bounce off another player when you accidentally collide. Moving air masses collide, too, but they do not bounce off each other. What happens where two air masses meet?

A boundary forms between air masses where they collide because a dense, cold air mass and a less dense, warm air mass simply do not mix together. The boundary where two air masses meet is called a weather front. There are four types of weather fronts—cold, warm, stationary, and occluded, as seen in Figures 2A and 2B. Fronts travel as the air masses move, and a passing front often brings sudden changes in weather. Scientists continuously gather data that allow them to identify the locations and possible movement of fronts. Using this data, scientists can predict the general weather patterns each front is likely to bring by knowing how fronts interact.

Cold Front A cold front is a weather front in which a cold air mass advances to replace a warm air mass. Cold air is denser than warm air.

So, the cold air pushes under and lifts the warm air. A cold front brings colder air, and you can feel the temperature dip as it passes. Cold fronts often bring stormy weather because the warm, lifted air cools and may condense to form cumulonimbus clouds in the upper atmosphere.

Cold fronts can pass through a location in only a few hours.

Cold and Warm Weather Fronts

Warm air mass

Cold front

Cold air mass

Direction of front

Warm air mass

Warm front

Cold air mass

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Direction of front

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Warm Front A warm front is a weather front in which a warm air mass advances to replace a cold air mass. When the dense, cold air mass moves ahead of the less dense, warm air mass, the warm air takes its place. Warm fronts can pass slowly through a location and are associated with stormy weather. However, the precipitation is steadier and gentler than at a cold front.

Stationary Front A stationary front is a boundary between a cold air mass and a warm air mass that are not moving. Like cold and warm fronts, a stationary front forms where a cold and warm air mass meet. However, neither air mass moves past one another. The weather at a stationary front is similar to that at a warm front. It may last for many days until the front begins to move to become a warm or cold front again.

Occluded Front An occluded front is a boundary between one warm air mass and two cold air masses, in which the warm air mass is pushed above the two cold air masses. Occluded fronts form when a cold air mass meets a warm air mass and a second cold air mass moves under the warm air mass, pushing the warm air above both cold air masses. Occluded fronts can bring light, moderate, or heavy precipitation.

Figure 2B A stationary front forms between a cold air mass and a warm air mass that cannot move past each other. An occluded front forms when two cold air masses meet one warm air mass and push it up above them. All fronts are associated with precipitation, but cold fronts tend to bring severe storms.

Stationary front

Stationary and Occluded Weather Fronts

Cold air mass

Warm

Warm air mass

air m

ass ss

r ma

Occluded front

ai Warm

Cold air mass Cold air mass

Direction of front

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3. Low Pressure and High Pressure Systems

Decreasing air pressure, as measured with a barometer such as this one, may mean a low pressure system is approaching. Cloudy, stormy weather may be on its way. Increasing air pressure means fair weather is likely because a high pressure system is approaching.

While stormy weather is associated with low pressure, fair weather is often associated with high pressure. Barometers can measure the changes in pressure that occur when a low or high pressure system is approaching. These changes in pressure data can be used to predict fair or stormy weather. How does air pressure relate to weather fronts and changes in weather?

A low pressure system is an area within the atmosphere where air is rising and winds blow toward the center. The diagram of the low pressure system in Figure 3 shows arrows modeling the directions that air flows. As you can see, the pressure is lowest at the center of a low pressure system because air is rising due to warmer temperatures. Air flows toward the center of the low pressure system to replace the rising air. As it does, it curves and whirls because Earth is spinning. The whirling mass of air forms the low pressure system, which is also called a cyclone.

A high pressure system is an area within the atmosphere where air is sinking and winds blow away from the center. Compare the high pressure system with the low pressure system in Figure 3. Notice that the air is sinking at the center—the pressure is highest there. Then, the air whirls away from the center, spinning in the opposite direction as a low pressure system. Because air flows in the opposite direction as a cyclone, high pressure systems are called anticyclones. In the Northern Hemisphere, an anticyclone curves in the clockwise direction.

Rising or sinking air can mean the difference between a fair or stormy day. A decrease in air pressure may mean a low pressure system is approaching, possibly bringing precipitation and strong winds. Clouds form because the rising air cools and can hold less water. The opposite happens in high pressure systems. The sinking air warms and can hold more water, causing clouds to evaporate. So, rising atmospheric pressure means a high pressure system may bring clear, fair weather.

Behavior of Low and High Pressure Systems

Figure 3 In a low pressure system, air whirls inward to replace air that is rising in the center. In a high pressure system, air whirls outward as it is pushed out by air that is sinking in the center. This rising and sinking of air can mean the difference between a cloudy, rainy day and a fair, sunny day.

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Rising air

L

Sinking air

H

Five-Day Weather Forecast Today

June 1 Thu

Scattered T-Storms 37°C

24°C

(98.6°F) High

(75.2°F) Low

June 2

T-Storms 33°C

26°C

(91.4°F) High

50%

(79°F) Low

80%

Fri

June 3

Sat

Sunny 37°C

26°C

(98°F) High

(78.8°F) Low

June 4 Sun

T-Storms 37°C

27°C

(98.6°F) High

0%

(80.6°F) Low

10%

4. Weather Reporting You have learned that air masses, weather fronts, and low or high pressure systems may cause changes in the weather. Suppose that you want to know whether you will need your umbrella on your walk home from soccer practice. Where can you find out what the weather will be?

You can find a local weather report in many places. Weather-related apps and websites provide reliable information about the weather almost anywhere in the world. Local TV stations and newspapers also give forecasts. Checking forecasts for weather can help you decide whether to take your umbrella or wear sunscreen.

Many five-day forecasts predict the daily temperature ranges and the chance of precipitation. Notice the forecast in Figure 4, with a column for each day. A quick look will tell you that today and tomorrow may be stormy, while Friday may be sunny. Detailed weather reports also include wind speed, humidity, and whether the air pressure is rising or falling.

Since weather patterns are very complex, scientists can only predict the probability, or likelihood, of a certain type of weather. For example, although they may predict thunderstorms on Thursday, you may not have a thunderstorm that day. The bottom row of Figure 4 shows the probability of precipitation. A higher percentage suggests precipitation is more likely to occur. Today, the probability of a thunderstorm is 50 percent, so the chance of a storm occurring where you are is equally as likely as the chance that there will not be a storm. On Thursday, the probability is 80 percent, so you are more likely to have a storm than not. Over the weekend the chance is only 10 percent. That suggests a storm is possible but not likely.

June 5

T-Storms 38°C

(100.4°F) High

27°C

(80.6°F) Low

10%

Figure 4 A simple five-day weather forecast summarizes the high and low temperatures for each day and the chance, or probability, of precipitation.

Scientists give the probability of precipitation as percentages because weather is so complex that they usually cannot predict the weather with absolute certainty.

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5. Weather Maps On weather sites, scientists may use a map of your area or the United States to explain the forecast. While these weather maps may look complicated, you already know almost everything that they include. What do they show?

Weather maps use symbols to show the location of fronts over a large area at a certain point in time. Fronts are represented by colored lines with triangles or semicircles. Warm fronts are shown by a red line with semicircles, while a cold front is shown by a blue line with triangles.

The semicircles or triangles point in the direction that the front is moving. Can you identify the weather associated with each type of front on the map in Figure 5? On the map, north of Montana, alternating red semicircles and blue triangles point in opposite directions, representing a stationary front. A purple line with semicircles and triangles pointing in the same direction represents an occluded front north of Michigan.

Weather maps also show low and high pressure systems. A low pressure system is represented by a large red “L,” while a high pressure system is shown by a large blue “H.” The lines around the Ls and Hs are called isobars. An isobar is a line on a weather map that connects places that have the same air pressure. The numbers near these lines indicate the pressure. Notice that the isobars show pressure decreases going away from an H and toward an L. Closer isobars mean the pressure is changing more quickly and winds will be faster.

Figure 5 Weather maps show the weather patterns within a certain point in time over a large area, such as the entire United States. They include symbols that represent each type of front that is occurring, low and high pressure systems, and isobars that show air pressure and how it changes.

Weather Map and Weather Symbols

1004

Rain

1008

1020

1008

Snow Cold front Warm front Occluded front Stationary front Isobar High pressure system Low pressure system

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1012

1012

1028

1032 1000 1020 1016

Key Science Concept

Relating Air Masses, Fronts, and Pressure Systems This weather map uses symbols to show the weather conditions on a winter day in the United States at 2 p.m., Central Standard Time. The models of the fronts show what is happening where the air masses meet. The photos show the actual weather in specific locations. How can you explain the weather at each location using the cause-and-effect relationships you have learned?

Cold front

Warm front

Boise, ID

Bismarck, ND

Topeka, KS

Springfield, IL

Albuquerque, NM

El Paso, TX

Orlando, FL

Augusta, ME

Stationary front

Occluded front 105

6. Tools of Weather Forecasting The weather forecast says that a cold front is moving through your area on Saturday. There is an 80 percent chance of thunderstorms, so the soccer game might be canceled. How do scientists determine that a cold front is moving toward your area?

What kind of data do scientists need to analyze and forecast weather? Scientists gather large amounts of data about the state of the atmosphere to make weather maps and accurately predict local weather. Weather stations, weather balloons, radar, and satellites measure atmospheric pressure, wind, temperature, humidity, and precipitation. Think back to the weather map in Figure 5. Pressure data from all over the United States were taken to make this map.

Scientists have placed thousands of weather stations all around the world to gather enough information to provide the evidence necessary to predict the weather. Weather stations include the tools scientists use to collect weather-related data on the ground: thermometers to measure temperature, barometers to measure pressure, anemometers to measure wind speed, rain gauges to collect and measure precipitation, and hygrometers to measure humidity.

Scientists also gather data about the conditions high up in the atmosphere using weather balloons and satellites. Weather balloons carry instruments that collect information from weather stations and satellites at altitudes of more than 30 km. As they rise, they transmit data about temperature, air pressure, wind speed and direction, and relative humidity at different altitudes. Satellites that orbit high above Earth accumulate data about temperature, humidity, and cloud cover.

This data is then translated into images for analysis. Scientists look for patterns in satellite images that provide evidence for how storms develop and change over the entire planet.

This is the Aqua satellite, which was launched by NASA to help answer questions about the water cycle. It collects and transmits data about clouds, precipitation, air temperatures, and other variables. Scientists use satellites like this along with weather stations and weather balloons to gather and analyze data in efforts to predict local weather.

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One of the most important tools scientists use to detect precipitation is radar. Radar antennas, such as the one inside the sphere on the tower in the photo, send out radio waves. These waves bounce off clouds, rain, snow, hail, or other types of precipitation. The antenna then detects these waves as they return. The radar can detect the intensity of the precipitation and the direction of the storm.

The resulting data is used to create maps of clouds and precipitation.

The maps can provide evidence that thunderstorms or snow clouds are forming.

Scientists accumulate data from radar, satellites, and weather stations and balloons to give current weather conditions. These data are then processed through computer models to analyze weather patterns and make a variety of forecasts. The models use mathematical formulas to find the probability of weather conditions and can predict how complex weather patterns can change. For example, they may predict that there is an 80 percent chance of rain on Saturday. That suggests there is a 20 percent chance that there will not be rain. But, an 80 percent chance of rain means you should be prepared for rain. Pack an umbrella.

Scientists use Doppler radar systems like this one to gather data about precipitation. They use computer models to analyze the data from radar, weather stations, instruments on weather balloons, and satellites, allowing them to predict complex weather patterns.

LESSON SUMMARY

Air Masses and Changing Weather Air Masses The large volume of air in an air mass has uniform temperature and humidity at a certain altitude. The properties of an air mass are determined by where the air mass forms. Air masses affect weather as they move around the globe.

Weather Fronts Weather fronts form where warm and cold air masses meet. Cold fronts, warm fronts, stationary fronts, and occluded fronts are each associated with typical types of weather.

Low Pressure and High Pressure Systems Low pressure systems form where air is rising. They are associated with stormy weather. High pressure systems form where air is sinking. They are associated with fair or clear weather.

Weather Reporting Weather forecasts are predicted using probability. A typical forecast includes possible high and low temperatures as well as the likelihood of precipitation and wind.

Weather Maps Weather maps use symbols to represent fronts and high and low pressure systems over a large area at a specific time.

Tools of Weather Forecasting Scientists use weather stations, radar systems, weather balloons, and satellites to gather weather data. They use computer models to analyze the data so that they can predict weather conditions.

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Severe Weather What is severe weather, and how do scientists predict where will it occur?

Introduction As it touches the ground and sucks up dirt and debris, the funnel cloud darkens. The tornado’s whirling winds will wreak havoc and cause damage for miles along its path. How can you tell if dangerous weather such as a tornado is on its way? What can you do to stay safe?

Severe weather can damage buildings, trees, and crops, cause power outages, shut down highways and bridges, and injure or even kill people. There are many kinds of severe weather, including blizzards, heat waves, severe thunderstorms, tornadoes, hurricanes, droughts, and ice storms. Severe weather conditions may cause additional dangers such as wildfires, landslides, or flash floods. The type of severe weather you need to prepare for depends on local weather patterns.

Maps of past severe weather can reveal patterns that show where similar events are likely to occur again.

In this lesson, you will learn about five kinds of severe weather. You will discover the damage they cause, where they are likely to occur, why they occur, and how to withstand their effects. You will also find out how weather forecasters analyze satellite and radar images so they can warn people of severe weather.

Vocabulary severe weather weather such as blizzards, heat waves, severe thunderstorms, tornadoes, and hurricanes that can damage build­ ings or cause loss of life blizzard a winter storm that lasts for at least three hours with winds greater than 56 km/h and large amounts of blowing snow heat wave a period of unusually hot, and often more humid, weather than is typical for a region heat index the temperature that the air feels like to people when humidity is combined with the actual air temperature severe thunderstorm a thunder­ storm that has wind speeds of 93 km/h, hail that is at least 2.5 cm wide, or a tornado tornado a rotating column of air with extremely high wind speeds of 117 km/h or higher that touches the ground hurricane a huge, rotating, low pressure storm system that forms over warm water near the equator and has sustained wind speeds of 119 km/h or higher

Next Generation Science Standards Performance Expectations MS-ESS3-2. Analyze and interpret data on natural hazards to forecast future catastrophic events and inform the development of technologies to mitigate their effects.

MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering Practices Analyzing and Interpreting Data Analyze and interpret data to determine similarities and differences in findings.

Developing and Using Models Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Crosscutting Concepts Patterns Graphs, charts, and images can be used to identify patterns in data.

Influence of Science, Engineering, and Technology on Society and the Natural World

Disciplinary Core Ideas ESS3.B. Mapping the history of natural hazards in a region, combined with an understanding of related geologic forces can help forecast the locations and likelihoods of future events.

ETS1.B. • A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. • Models of all kinds are important for testing solutions.

ETS1.C. The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

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1. Blizzards

Blizzards are particularly dangerous winter storms with high winds and poor visibility that can cause freezing conditions and loss of life.

This satellite image of a major winter storm hitting the East Coast of the United States was taken by NOAA’s GOES-16 satellite in 2018. Using images such as this, along with other data gathered from monitoring the storm system, helped the NWS in issuing a blizzard warning for the Mid‑Atlantic region of the country.

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Winds howl and snow swirls all around. Luckily, school was canceled because of a severe weather warning—a blizzard. How is severe weather different from other types of weather?

Severe weather is weather that can damage buildings or cause loss of life. It includes blizzards, heat waves, severe thunderstorms, tornadoes, and hurricanes. The National Weather Service (NWS) is the official U.S. agency that monitors the weather. The NWS is authorized to issue storm watches and warnings to inform people of severe weather events.

A blizzard is a winter storm that lasts for at least three hours with winds greater than 56 km/h (34.7 mph) and large amounts of blowing snow. As seen in the photo, visibility is nearly zero because so much snow is blowing. Below-freezing temperatures create icy conditions on roads and sidewalks that make driving and walking hazardous. The very low wind chill temperature increases the chance for frostbite, or damage to the skin from freezing, and hypothermia. Hypothermia occurs when body temperature falls below 35°C (95°F) and internal organs begin to fail. During blizzards, piles of snow can block roads, cause power outages, and trap some people in their homes for days.

Understanding how blizzards form and where they are likely to happen allows the NWS to warn people of an approaching storm.

Blizzards develop when a low pressure system has formed where moist, warm air rises over cold air, producing lots of snow and high winds.

The NWS analyzes data from satellite images, weather stations, and weather balloons for potential blizzard activity. The NWS also keeps historical data of blizzards by city and region so it can predict where future ones are likely to occur. The data show that blizzards in the United States are common in the Midwest, the Northeast, and mountainous areas. What clues in the satellite image show which section of the country may be experiencing a blizzard?

2. Heat Waves You have probably never experienced a blizzard if you live in southern California or Florida. But you may have been very hot in the summer. Beyond uncomfortable, when is hot weather hazardous?

A heat wave is a period of unusually hot, and often more humid, weather than is typical for a region and can be very dangerous. A heat wave lasts at least two days or longer. The hot temperatures can harm people, particularly elderly people and babies, and people without air conditioning. Heat waves can be more dangerous in cities than the surrounding areas. This is because buildings and concrete make cities hotter. Heat waves also increase the risk of wildfires.

During a heat wave, people are in danger when they cannot maintain normal body temperature. They may suffer heatstroke when the body temperature rises above 41°C (106°F). Heatstroke needs to be treated right away. If it is not, the person may suffer permanent brain damage and even die. Hundreds of people die each year in the United States due to hot temperatures.

Humidity makes things worse during a heat wave because sweat does not evaporate well in humid air. So, the body cannot cool itself efficiently and the air temperature feels hotter. The heat index is the temperature that the air feels like when humidity is combined with the actual air temperature. For example, when relative humidity is 75 percent and the air temperature is 32°C (90°F), the heat index is 43°C (109°F). That is dangerously hot.

Heat waves occur in many parts of the United States in the summer.

To predict heat waves, forecasters look for increasing temperatures and humidity within high pressure systems stalled over a region. Air that is sinking in the middle of a high pressure system keeps the hot air near the ground from rising. The trapped air gets hotter because it is under pressure and because the ground heats up during fair, sunny weather and transfers thermal energy to the air.

People can lessen the effects of a predicted heat wave. Some people may buy air conditioners or fans to stay cool. Cities may open cooling centers in public buildings, such as libraries, where people can stay cool. To avoid heatstroke during a heat wave, you should avoid strenuous activities, stay out of the sun, and drink plenty of water.

It is important to stay cool during a heat wave, which is a period of unusually hot and often humid weather. The heat index is the temperature that tells you how hot it actually feels during a heat wave because of high humidity.

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Lightning, thunder, and heavy rain are a part of every thunderstorm.

A severe thunderstorm also has high winds, large hail, or a tornado. So, it can be very destructive. You should seek shelter during a thunderstorm and stay away from windows and corded electronic devices in case of a lightning strike.

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3. Severe Thunderstorms Dark clouds, bright flashes of lightning, booming claps of thunder, and pouring rain mean one thing—a thunderstorm. While some think a thunderstorm is more frightening than a heat wave, most thunderstorms are not classified as severe weather. So, how are severe thunderstorms different?

A normal thunderstorm includes lightning, thunder, and heavy rain. A severe thunderstorm is a thunderstorm that has wind speeds of greater than 93 km/h (57.7 mph), hail that is at least 2.5 cm (0.98 in.) wide, or the development of a tornado. A severe thunderstorm may last for several hours and has the potential to be much more destructive than ordinary thunderstorms. The very strong winds may blow down trees and power lines. Hail can damage cars and plants, and harm animals that do not have shelter from the storm. Heavy rains may also cause flash flooding. Trees and buildings may be struck and burned by lightning or damaged by wind and floodwater. After a severe thunderstorm, people may be without power and roads may be blocked by downed trees or floodwater.

You can take steps to protect yourself before a severe thunderstorm.

During any thunderstorm, go inside or seek shelter, and stay away from windows. Avoid trees, water, and electrical devices with cords to reduce your risk of getting struck by lightning. Never try to cross roads that are flooded by water, even if you are in a car, because a car can be carried away in waters less than a foot deep.

Understanding how thunderstorms form helps scientists predict severe thunderstorms. To do this, scientists must use a variety of data received from satellite and radar imagery. They look for tall clouds and a large amount of precipitation in satellite images. They also look for specific wind patterns in radar images.

Most thunderstorms develop where warm, moist air near the ground meets cold, dry air above it. The warm air may be pushed up at a cold front, causing the water in the air to condense to form a large cumulus cloud as seen in Figure 3. As the air continues to rise as an updraft, the cloud grows into a tall cumulonimbus cloud. Precipitation starts to fall and a downdraft, or cool air that is moving downward, develops. In normal thunderstorms, the cool downdraft eventually dominates over the warm updraft, ending the updraft and the storm.

In a severe storm, the warm updrafts and cool downdrafts are farther apart, allowing the storm to grow bigger. Strong updrafts continue to feed the storm and push ice particles upwards, forming them into hail. A funnel cloud may also develop if a thundercloud starts to spin, rotated by strong winds.

The frequency of severe thunderstorms depends on where you live.

There are about 10,000 severe thunderstorms in the United States each year. Most of these occur in the middle of the country between Texas and Minnesota. Regions with severe thunderstorms are also likely to have tornadoes, when developing funnel clouds touch ground.

Figure 3 Severe thunderstorms can form at cold fronts where warm, moist air is pushed upwards. All thunderstorms form as the water vapor in the rising air condenses to form a cloud that grows into a cumulonimbus cloud. In severe thunderstorms, the updrafts and downdrafts are separated, allowing the storm to grow bigger and create hail.

Formation of a Severe Thunderstorm Cumulonimbus cloud Anvil top Wind

Updrafts

Storm direction

Downdrafts Cold air

Warm, moist air Rain, hail, lightning

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4. Tornadoes

Hook echo

This radar image shows a “hook echo” forming within a severe storm. A hook, such as this one, indicates favorable conditions for a tornado.

Figure 4 This map shows the average number of tornadoes that occurred across the United States during the month of June for the time period from 1989–2013.

A tornado like the one in the photo at the beginning of this lesson typically lasts just a few minutes, but it can leave a trail of destruction in its path. What is a tornado, and how can people stay safe during one?

A tornado is a rotating column of air with extremely high wind speeds of 117 km/h (73 mph) or higher that touches the ground. The damage done by a tornado is proportional to wind speed, so the higher the winds, the more destructive they are over a relatively small area.

Tornadoes can knock down power lines, uproot trees, rip off rooftops, destroy buildings and scatter debris. Flying debris can be highly dangerous. After a tornado, people may be left homeless or without power, natural gas lines can be damaged causing leaks that increase the risk of fire, and survivors may face months of rebuilding.

More than 1,000 tornadoes occur in the United States every year.

Florida, and the states in Tornado Alley, including Texas, Kansas, and Oklahoma, experience the most tornadoes. Figure 4 shows the average number of tornadoes that occurred each June from 1989–2013.

Scientists are working to understand exactly how tornadoes develop by using satellite and radar images. They know that tornadoes often form during severe thunderstorms. Specific patterns such as the characteristic “hook echo” in radar images may indicate a tornado is forming.

The shape of the hook is formed from strong drafts of wind blowing downward as precipitation is wrapped around strong drafts of wind blowing upward.

In places where tornadoes are common, local governments often use sirens to warn people about tornadoes. Some buildings also have underground storm shelters where people can stay during a tornado. If you cannot get to a storm shelter, seek refuge in a basement or a room away from windows and outside walls, such as a hallway.

Tornado Occurrences in the United States

Number of tornadoes >10 9–10 7–8 5–6 3–4 1–2 <1

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Satellite Image and Model of a Hurricane Rising, warm, moist air condenses as clouds Wind speed: 120.7 km/h Eye Eyewall

Warm, moist air rises rapidly in updrafts near the center Rainbands

5. Hurricanes People in Kansas or Oklahoma need to be prepared for tornadoes.

But, they are unlikely to experience a hurricane like people who live along the Gulf Coast or East Coast. What is a hurricane, and why do they only affect certain parts of the country?

A hurricane is a huge, rotating, low pressure storm system that forms over warm water near the equator and has sustained wind speeds of 119 km/h (73.9 mph) or higher. Like other low pressure systems, hurricanes that form in the Northern Hemisphere rotate counterclockwise. Satellite images, such as the one in Figure 5A on the left, show the rotating pattern of the clouds. The clouds span an area over the Bahamas and Cuba off the southeast coast of Florida.

Hurricanes form as warm air travels over warm oceans. Water evaporates, making the air very moist. As the air rises, it cools and water vapor condenses to form clouds. Energy is released by condensation into the air and fuels the growing storm. The less dense warm air continues to rise, creating a low pressure system. At the bottom of this system, warmer, moist air flows in to replace the rising air. Strong winds form. The clouds may begin to rotate noticeably, forming a tropical storm, which may continue to grow into a hurricane if atmospheric conditions are right.

Figure 5A also shows a model of the resulting structure on the right.

The eye is the center of the hurricane, where air pressure is lowest near sea level compared to the rest of the storm. Inside the eye, winds are relatively calm and the sky is clear, as seen in the photo. The eyewall is a wall of tall cumulonimbus clouds that surrounds the eye. Strong thunderstorms and the highest winds in the hurricane occur here.

The spiraling bands of clouds and rain around the eyewall are called rainbands. Rain can occur between these bands but is very heavy inside of them and accompanied by intense winds.

Figure 5A The satellite image on the left shows a hurricane, which is a huge, rotating storm system with extremely high winds. The model of the hurricane on the right shows its structure.

This photo taken from a NOAA P-3 hurricane hunter aircraft shows the eye and the dense eyewall of Hurricane Katrina.

Eyewall

Eye

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Hurricane Paths from 1985–2005

Saffir-Simpson Hurricane Wind Scale Category

Five

Four

Three

Two

One

Tropical storm

Tropical depression

Wind speed (km/h)

≥252

209–251

178–208

154–177

119–153

63–118

≤62

Figure 5B This map shows the paths of various hurricanes over a 20-year period. Each path is shown in a different color, depending on the strength of the storm as categorized by the Saffir-Simpson Hurricane Wind Scale. The 1 to 5 rating categorizes hurricanes based on sustained wind speed and the amount of resulting property damage.

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Figure 5B shows the history of hurricane paths from 1985–2005. It was created using data collected by the NWS and the U.S. military. The lines show that the hurricanes formed near the equator and their paths follow a general pattern, often moving in a west-northwest direction.

Hurricanes are most likely to form during certain times of the year.

In the North Atlantic Ocean, hurricane season is from the beginning of June to the end of November, when the water there is warmest. On average, six hurricanes form in the Atlantic each year, but they do not all reach land. Why do hurricanes that form in the Eastern Pacific Ocean rarely reach the West Coast of the United States? This same west-northwest movement pushes them away from the West Coast and weakens the storm. The ocean there is cold, so it does not have enough thermal energy to sustain hurricanes.

Hurricanes that reach land bring dangerously high winds and heavy rains that can cause flooding to a wide area near landfall. They also cause a storm surge, which is a rise in ocean water that may be up to 6 meters high. Storm surges can cause massive flooding. As the storm moves over land, it quickly becomes weaker because warm ocean water no longer provides water and energy. But, the storm can still bring heavy rains and flooding to inland areas.

Scientists use satellite and radar images to track storms that may develop into hurricanes. They also send airplanes into the storm to collect data about the conditions inside the storm. Computer models help scientists predict whether a storm will turn into a hurricane and what path it is likely to follow. Historical maps, such as Figure 5B, that show the formation and movement of past hurricanes, are also used to help forecast future storms. If the models predict that a hurricane may reach land, the NWS has time to issue a warning.

Key Science Concept

Severe Weather Safety Historical data and maps of severe weather reveal patterns in where and how often severe weather occurs in different regions. You should know how to get information about severe weather risks and be sure to act in response to a watch or warning. Developing and following an emergency plan for the kinds of severe weather that occur in your area will help you and your family stay safe.

I live in Oklahoma where about 60 tornadoes occur every year. Some are mild while others are violent.

We have an underground storm shelter where I go when I hear the tornado warning siren.

In Louisiana, we can get strong winds, heavy rains, and storm surges. Once every 3 to 11 years or so, we get a hurricane. To prepare, we gather supplies and board up windows. If it floods, we may evacuate.

In Florida, we can get heat waves. Between 1997 and 2017, we have had five heat waves. When one occurs, I avoid exercising outside, drink lots of water, and stay inside where there is air conditioning.

In Nebraska, we can get lots of snow and ice storms with a 50 percent chance of a blizzard in any given year.

During blizzards, we stock up on supplies and stay inside if possible. We limit our time outside and dress warmly.

You can follow these steps: 1

Know your risks

Identify what types of severe weather occur where you live and when they occur.

2

Do your research

Learn how to prepare for storms from sources like the National Weather Service.

3

Plan and prepare

Make an emergency plan and kit with your family. Know where shelters are located.

4

Listen to watches and warnings

Watches mean severe weather may occur.

Warnings mean that severe weather is happening.

5

Follow the emergency plan

Listen to official guidelines. Stay inside until the severe weather is over, but evacuate if necessary.

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Engineering Design

Scientists use storm data to test storm-forecasting models to predict severe weather events such as tornadoes and flash floods up to an hour before they strike.

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6. Improving Severe Weather Forecasting For regions that have a history of tornadoes, a warning system is especially important. As of 2017, warnings are sometimes issued less than 13 minutes before the tornado strikes. Those few minutes are not much time for some people to get to a safe place. However, forecasters presently have no way to predict tornadoes further in advance. They can only issue a tornado warning after they observe signs in radar data that a tornado is forming. What are scientists doing to develop a faster and more accurate way to forecast severe weather?

The NOAA National Severe Storms Laboratory continues to develop and improve a state-of-the-art computer modeling system to accurately predict severe weather, including tornadoes, thunderstorms, and flash floods. The main criterion is that the system is able to issue warnings 30 to 60 minutes in advance to save more lives. The system combines many computer-based weather models, so it can produce more detailed outputs. For example, it can predict the likely path of a tornado and will allow forecasters to predict tornadoes before they can be observed on the radar. To do this, computers calculate complex equations using a large amount of weather data. Running the models requires a huge amount of computer power.

Before these systems become operational, they must be tested, improved, and tested again. To develop the models in the system, both records of historical severe weather events, and a database of specific severe weather events were used. This includes events such as severe thunderstorms that form or do not form a tornado. The data are compiled from historical maps, radar, satellites, and weather balloons and stations. These data are entered into computer models as input.

The predictions of the models, or output, are compared to the actual observations of an occurring storm. Models are constantly refined and retested to accurately predict the weather.

The system is then tested using real-time weather data at the Hazardous Weather Testbed (HWT). The HWT specializes in testing forecasting and warning methods. The system is tested by scientists working on the models and by the forecasters who will use the system.

Here, the system is further optimized to accurately predict where a tornado will strike. It is also improved so that forecasters can easily use it to issue tornado warnings.

Would an extra 45 minutes of advanced warning help people to better prepare in the event of a tornado? Developing and testing the computer modeling system will improve scientists’ ability to forecast tornadoes accurately and provide warning in advance.

LESSON SUMMARY

Severe Weather Blizzards Severe winter storms such as blizzards can create icy conditions and power outages, block roads with snow, and result in loss of life. Historical data of blizzards help the National Weather Service predict where future ones are likely to occur.

Heat Waves A period of weather that is unusually hot and humid for a region is known as a heat wave.

To predict heat waves, forecasters look for increasing temperatures and humidity.

Severe Thunderstorms In addition to lightning, thunder, and heavy rain, severe thunderstorms have strong winds and large hail. To help predict severe thunderstorms, scientists look for tall clouds and large amounts of precipitation in satellite images, and wind patterns in radar images.

Tornadoes Tornadoes are rotating columns of air that touch the ground. Scientists identify specific patterns in satellite and radar images that may indicate a tornado is forming and where it will touch ground. They use these data to provide advanced warnings.

Hurricanes Hurricanes are large, rotating, low pressure systems with wind speeds of at least 119 km/h.

Historical maps showing the formation of hurricanes and hurricane paths can help forecast future storms.

Improving Severe Weather Forecasting Computer modeling combines current and historical models to predict severe weather. Storm warning models must be tested, improved, and retested.

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Traits

ANCHORING PHENOMENON Organisms have unique physical and behavioral traits that help them survive.

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Phenomenon-Based Storyline Plan an eco-tour of Madagascar, an island that has plants and animals that exist nowhere else on the planet, and highlight how the unique traits of Madagascar’s organisms have helped them survive.

Next Generation Science Standards Performance Expectations MS-LS1-5.

Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.

MS-LS1-4.

Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.

MS-ETS1-1.

Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

MS-ETS1-4.

Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering Practices Constructing Explanations and Designing Solutions Construct a scientific explanation based on valid and reliable evidence obtained from sources (including the students’ own experiments) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

Engaging in Argument from Evidence Use an oral and written argument supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem.

Asking Questions and Defining Problems Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions.

Developing and Using Models Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Crosscutting Concepts

Disciplinary Core Ideas

Cause and Effect Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.

LS1.B. Growth and Development of Organisms • Genetic factors as well as local conditions affect the growth of the adult plant. • Animals engage in characteristic behaviors that increase the odds of reproduction. • Plants reproduce in a variety of ways, sometimes depending on animal behavior and specialized features for reproduction.

Influence of Science, Engineering, and Technology on Society and the Natural World • All human activity draws on natural resources and has both short and long-term consequences, positive as well as negative, for the health of people and the natural environment. • The uses of technologies and limitations on their use are driven by individual or societal needs, desires, and values; by the findings of scientific research; and by differences in such factors as climate, natural resources, and economic conditions.

ETS1.A. Defining and Delimiting Engineering Problems The more precisely a design task’s criteria and constraints can be defined, the more likely it is that the designed solution will be successful.

Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions.

ETS1.B. Developing Possible Solutions • A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. • Models of all kinds are important for testing solutions.

ETS1.C. Optimizing the Design Solution The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

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Traits for Survival How do organisms meet their needs and respond to threats in their environment?

Vocabulary starvation to suffer or die from lack of food dehydration an abnormal and excessive loss of water from the body of an organism suffocation to suffer or die from lack of oxygen.

Introduction These jaguars may have been resting and playing when the photo was taken, but their lives aren’t always so relaxing. A jaguar’s environment contains dangers that threaten the animal’s survival. For example, a shortage of food or water might mean that the jaguar could die of hunger or thirst. How can an animal survive in spite of these threats?

All living things have many traits that help them survive. Traits like a jaguar’s whiskers sense movement in the environment. This alerts the jaguar to nearby food or other animal hunters. Its sensitive nose detects smell. If the jaguar detects a potential meal, its tan fur and black spots blend into the speckled light in the forest and allows the jaguar to be hidden from prey animals. The jaguar’s long, sharp teeth and powerful jaws help it to kill its prey. Although none of these traits can guarantee that the jaguar will survive the threats from the environment, all these traits contribute to the increased chance that the jaguar will survive.

This lesson sets the stage for understanding cells and heredity by exploring the traits of living things. First, you will learn about what organisms need to survive. Then you will explore traits that help organisms get what they need to survive and avoid threats along the way. You will learn that traits can be passed down from parent to offspring. You will also learn that traits can be inspiration for engineers who design products. Finally, you will link causes to effects as you think about how environmental factors influence some traits.

predation a relationship between two organisms in which one of them captures and feeds on the other physical trait a distinct feature or body part of an organism behavioral trait a distinct way in which an organism interacts with its environment species a group of living things that share traits and can breed successfully with each other, but not with other groups

Next Generation Science Standards Performance Expectations MS-LS1-5. Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.

MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

on valid and reliable evidence obtained from sources (including the students’ own experiments) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.

Asking Questions and Defining Problems Define a design problem that can be solved through the development of an object, tool, process or system and includes multiple criteria and constraints, including scientific knowledge that may limit possible solutions.

Science and Engineering Practices Constructing Explanations and Designing Solutions Construct a scientific explanation based

Crosscutting Concepts Cause and Effect Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.

Influence of Science, Engineering, and Technology on Society and the Natural World Disciplinary Core Ideas LS1.B. Genetic factors as well as local conditions affect the growth of the adult plant.

ETS1.A. The more precisely a design task’s criteria and constraints can be defined, the more likely it is that the designed solution will be successful.

Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions.

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1. Organisms’ Survival Imagine that you were dropped off in the wilderness for a few days. What would you need to survive?

How would you get those things? How would you avoid dangers in the environment?

Needs for Survival Organisms can be very different, but they all have needs to survive. All organisms need energy, materials, and living space.

They acquire their needs from their environment.

Many types of organisms, including animals, need food. Food supplies energy and nutrients such as sugars, fats, proteins, and minerals that the organism needs to function. Whether an animal eats meat, plants, or both, the animal gets its food from its environment. Without food, an animal might starve.

Starvation, to suffer or die from lack of food, is a serious threat to an animal’s survival.

Animals also need water and oxygen to function.

They get water either by drinking it or by eating food that contains water. Structures such as lungs or gills take in oxygen from the environment. Animals can die if they do not take in enough water or oxygen to meet their needs. An abnormal and excessive loss of water from the body of an organism is called dehydration. A drought, a lack of rainfall over a long period of time, might cause dehydration. Suffocation is to suffer or die from lack of oxygen.

Plants have needs for survival too. Plants don’t have to eat food because they make their own, but they must take in nutrients such as water and minerals. Many kinds of plants have parts called roots and take in the nutrients that the plant needs through those roots. Plants also need sunlight, carbon dioxide from the air, and space to grow. Leaves collect light from the sun and take in carbon dioxide from the air that surrounds the plant. The plant gains space to grow by crowding out other plants.

When their needs are not met, organisms will die. Lack of water during a drought has caused many of these wheat plants to die. Animals that rely on the wheat for food may die of starvation if they cannot find another food source.

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Threats to Survival Organisms also have to avoid dangers in their environment to survive. So, an organism’s survival is dependent not only on its ability to meet its needs but also on its ability to survive environmental threats. There are many environmental causes that can have an effect on survival. What threats could an organism face that might challenge its survival?

The survival of organisms can be threatened by the danger of being eaten by other organisms. The relationship between two organisms in which one captures and feeds on the other is called predation. Predators eat prey. For example, a jaguar might eat a deer. A lack of prey can cause predators to starve. On the other hand, too much predation can severely decrease the numbers of prey.

Organisms can also be threatened by extreme temperatures. They will not be able to survive if they get too hot or cold. Many animals need shelter or body coverings for protection against this threat. For example, some birds build nests to lay their eggs. Nests can help keep the eggs or young chicks warm. Feathers also help birds stay warm and avoid getting too cold in their environment.

Another threat to an organism is the risk of diseases. All organisms can get some kind of disease, like a bacterial infection. Diseases weaken an organism and make it difficult for it to be able to meet its needs. Additionally, organisms that are already dehydrated or starving have a higher risk of getting a disease because their bodies are not functioning normally. For example, if bacteria invaded an organism’s body, a healthy organism can usually fight off the invaders. However, an organism that is struggling to survive might not be able to.

To avoid threats to their survival, these robins have built a nest in the trees.

The nest helps the young chicks stay warm. Living in the trees helps them avoid predators on the ground.

A leopard needs food to survive. It will hunt and kill other animals, like deer, to meet its need for food. Predation such as this is one of the factors that threaten the survival of certain organisms.

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2. Physical Traits and Survival You may know that knights wore armor for protection against attacking enemies. Like a knight, a turtle has an armor-like shell that covers its body. Similarly, an alligator has thick scales for protection.

Every organism has many physical traits that help it meet its needs or help it to survive threats to its survival. Shells and scales are examples of physical traits that help an organism survive. A physical trait is a distinct feature or body part of an organism. Some physical traits protect organisms from predators, while others help them avoid dehydration, starvation, or even extreme temperatures.

Many insects have physical traits that help them hide from predators.

The “leaf” you see in the center of this photo is actually the wing of a katydid that mimics the shape, color, and texture of a leaf. This camouflage might help the katydid survive because a bird or other predator may not be able to find it in a tree.

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Protection from Predators Many animals use physical traits for protection against predators. Some types of animals have sharp teeth, claws, and hooves that they can use when attacked. In addition, many animals hide from predators by using camouflage, which is a way to blend into the surroundings. For example, the katydid insect shown in the photograph has wings that mimic green leaves. A predator cannot differentiate between the insect and the plant that the insect is on, so the insect is not eaten. Octopuses have a different method of camouflage. They have pigment-containing structures in their skin that cause the skin color to change so that it matches the color of the octopus’s background.

Plants, too, have physical traits that protect them from predators. If you have ever tried to touch a cactus plant, you may have been pricked by its spines. Many kinds of plants produce spines, prickles, or thorns along their branches and stems. Roses, cactuses, and honey locust trees are only a few examples. How do these sharp structures help a plant survive? Imagine an animal that tries to eat a thorny plant. The animal would get a mouthful of thorns. This painful experience teaches a predator to keep away from thorny plants in the future. Another physical trait for dealing with predators is to have small hairs on the leaves or stems of a plant. These specialized hairs provide physical protection against insects. Some insects are blocked from eating fuzzy leaves because they cannot reach the leaf through the thick fuzz. Some of these fuzzy hairs even release chemicals that sting and deter the predator.

Protection from Dehydration Many plants and animals have physical traits that help them meet their needs for water and protection against dehydration. For example, plant roots help a plant get the water it needs to survive and grow. To protect themselves from dehydration, cacti have physical traits that help them survive. Their thick stems store large amounts of water that the plants can use when conditions are dry.

Animals also have physical traits for saving water. Camels can drink huge amounts of water in a very short time when it is available. They are able to retain that water in their blood, so they don’t need to drink as often as other animals.

Protection from Starvation Organisms also have physical traits that can help them get food or protect them from starvation. A long narrow beak helps a woodpecker bird get a meal out of a small hole in a tree better than a bird that has a broad beak. Although they do not eat like animals do, plants have structures in their leaves that help them make food. Like the cactus stores water, some plants store excess food to help prevent starvation. Beets, carrots, and potatoes store food in their roots. A plant that has stored food is less likely to starve at times when it is more difficult to make its food, like over the winter. The humps on a camel’s back are also physical traits that protect against starvation. A camel stores fat in its humps. This fat can be broken down for energy and nutrients when food is hard to find.

Protection from Extreme Temperatures Animals that get too hot or too cold are likely to die, so extreme temperatures are a threat to their survival. Fur, skin, feathers, and fat layers are physical traits that protect an animal against extreme heat or cold. Many animals that live in cold climates have thick fur and thick layers of fat. Other animals that live in warm climates have thin skin, little fat, and less fur. Horses have many sweat glands. This physical trait helps them sweat and stay cool in warmer temperatures.

This woodpecker’s long narrow beak helps it get a meal of insects out of a small hole in a tree. Its beak shape is a physical trait that helps the woodpecker avoid starvation.

Camels often live in dry deserts and are at risk for dehydration and starvation. They have physical traits that allow them to hold more water in their blood than other animals so that they do not dehydrate. They can also store food in the form of fat in their humps, so they do not starve when they cannot find food.

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Key Science Concept

Physical Traits for Survival All organisms have physical traits, structures that often help them survive in their environment. These traits increase the chance that an organism will fulfill its needs despite threats to its survival in its environment.

As you look at each example, think of other examples of plant and animal physical traits that help them meet survival needs.

Preventing Water Loss This succulent plant stores water in its thick leaves. This physical trait allows the plant to survive on dry, rocky soil without dehydrating.

Temperature Regulation The flower bud of this magnolia tree is covered with a layer of fuzz. This physical trait protects the flower from the cold until the flower blooms and breaks out of its protective covering.

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Obtaining Food The koala’s sharp claws are one of its physical traits. They help grasp the trunks of eucalyptus trees so that the koala can collect the leaves that it eats to prevent starvation.

Obtaining Oxygen This is a close up image of a fish’s gills. They are found on the side of the fish’s head. Gills are one of the physical traits that fish and some other marine animals use to breathe. A fish swallows water, and its gills extract the oxygen that is dissolved in the water.

3. Traits Inspire Design Humans have physical traits that make them well-suited to warmer environments. Humans are less suited to survive where it is cold because they do not have fur, feathers, or blubber that other animals have to keep them warm. How do humans manage to survive in cold climates?

People invented clothing to keep warm more than a hundred thousand years ago, possibly by observing the physical traits of other animals and collecting natural resources from the environment. By the early 20th century clothing filled with down feathers, the light and fluffy feathers found on birds like ducks and geese, was made.

Criteria and Constraints Down-filled jackets are good for many situations, but they aren’t perfect. These jackets are very light, easy to pack into a small space, and very good at keeping someone warm in dry weather. But they generally do not stay warm when they are wet.

In the 1980s, the United States Army began looking for new materials to use in jackets that had all the benefits of down and could also keep soldiers warm when wet, even if they were swimming in cold water for up to ten minutes. So, the material had to be water resistant and dry quickly. These were the Army’s specific criteria, or requirements for a successful design, that the material had to meet.

It was also important to the Army that the solution not be too expensive because the Army had many soldiers to clothe. This cost restriction was a constraint, or a limitation on an engineering solution.

Engineers had to consider both the Army’s criteria and constraints while they were designing their new material. The precise understanding of the criteria and constraints allowed the engineers to design a jacket that was likely to fit the needs of the Army.

Engineering Design

The shape of goose down feathers makes them very good at trapping air and therefore keeping the animal warm. One criterion for a new jacket filling for the United States Army was that it would be as good at preventing heat loss from the body as goose down feathers.

Geese have feathers that can help keep them warm. Their down feathers, found below the outer layer of feathers, are often used by humans for insulation in jackets or camping gear. Animal traits are often used as inspiration for engineering designs.

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This United States Army soldier wears a thick jacket to stay warm in a cold climate. The design for modern army jackets was inspired by traits that other animals have for staying warm. For example, the artificial down stuffing in a jacket was designed to have some of the beneficial qualities of goose down feathers.

Designing a Solution To meet the Army’s criteria and constraints, a company designed an artificial version of down feathers. This artificial down was designed in a lab. It was made to have a similar structure to down feathers. The small fibers trap air in a similar way to down feathers, which make them very good at keeping someone warm.

This material was able to satisfy most of the criteria; it was nearly as warm as down when dry, but it was better than down at keeping someone warm even when it’s wet. It was mostly water resistant and could dry out in less than 30 minutes. It was also lightweight and easily compressed into a small space. It also satisfied the constraints because it was cheaper to make artificial down jackets than real down jackets.

The material was so successful that it is now also used in jackets sold to the general public.

Revising Criteria and Constraints The creation of this down alternative solved another problem in addition to the problem that the Army was trying to fix.

It created a method for making jackets that did not require raising geese. Not only is raising geese expensive, some people object to the potential pain or death caused to these animals when their down feathers are removed.

Some companies have decided to only use artificial down. In these cases, the companies have included another constraint in their design process. This additional constraint is influenced by a societal value of treating animals humanely.

Criteria and constraints are considered and chosen every time there is an engineering problem. They can also be changed depending on new information, new technology, or new problems.

The criteria and constraints for every problem are generally chosen based on human needs, the natural resources available, the costs involved in designing the solution, and societal values.

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4. Behavioral Traits and Survival When your pet dog sees a stranger, it may bark to warn you that a stranger is nearby. The stranger may be a possible threat or an intruder in the dog’s territory. Barking is a trait of dogs, but it is not a physical trait. It is a behavior, or a way of acting.

Behaving a certain way might help an animal survive a threat to its survival by helping it to avoid danger. A behavioral trait is a distinct way in which an organism interacts with its environment. For example, some lizards run up to treetops when they sense a predator on the ground. Other animals, like opossums and some reptiles pretend to be dead when faced with a possible predator, a behavior known as apparent death. Apparent death helps a prey animal in multiple ways.

Predators are less likely to pay close attention to an animal that they think is already dead, so when the predator looks away, the prey can try to escape. Additionally, many predators don’t want to eat an already dead animal and will leave the animal alone.

Some animals have behavioral traits that distract predators and allow the animal to escape. When a regal horned lizard encounters a wolf or bobcat, it squirts blood from blood vessels around its eyes. The blood surprises the predator and irritates its skin and eyes, so the lizard has a short period of time to escape.

Predators are more likely to hunt an organism that is easier to kill and eat. Animals such as pufferfish use this to their advantage. They can inflate their bodies into the shape of a spiky ball. This makes them much more difficult to bite and less likely to be attacked. Similarly, armadillo lizards bite their own tails to form a ring. With scales on its back, the lizard becomes an armored ring, deterring many predators.

Plants have behavioral traits, too. For example, most plants will lean toward light to capture the most energy possible from the sun. You can observe this behavior if you put a plant near a window. Plants will also grow roots that reach toward a water source. These behaviors help the plant make food and survive.

Armadillo lizards are small lizards.

To discourage predators from eating them, they bite their own tails to form a ring. When their body is in a ring, it makes them into an armored ring that a predator might not want to eat.

These are pufferfish. The one on the right has collected water into its belly so that it looks larger and its spines stick out in response to a perceived threat. This behavioral trait helps these fish survive predation.

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Rainbow Trout Physical Traits and Their Environment River Rainbow Trout

Ocean Rainbow Trout

Figure 5A The smaller, pinkish rainbow trout spends its life in streams or rivers. The larger, silvery rainbow trout lives most of its life in the ocean. Although both fish are the same species and looked similar when young, the environment has played a large role in their color, size, and behavior.

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5. Environmental Influences on Traits Organisms have all kinds of different traits. Some traits the organism keeps for its whole life. Other times, the traits change over time. Some traits even change in response to the environment. For example, if you keep a chameleon as a pet, you might notice that its skin changes color when it is around something that it thinks is a predator, like your pet cat.

There are lots of cause and effect relationships between the environment and traits. The environment can influence an organism’s traits even when the organism isn’t threatened. For example, rainbow trout are all born in freshwater streams or lakes, but some migrate and spend most of their life in the ocean. Although they are the same species, the rainbow trout that move to the ocean end up looking different than the rainbow trout that stay in the rivers or lakes. A species is a group of living things that share traits and can breed successfully with each other, but not with other groups. After a few years, the rainbow trout that move to the ocean are larger than rainbow trout that live mostly in rivers. As you can see in Figure 5A, river and ocean rainbow trout are different colors as well as different sizes. River trout are yellowgreen with a pink stripe; ocean trout are silver and less colorful. It is the different environments that influence the changes in the rainbow trout’s physical traits.

Plants’ traits are influenced by their environment, too. Two plants of the same species, growing in different environments, might end up with different traits as they grow. For example, one plant might be larger because it had more sunshine, more water, or both. If the larger plant received more sunlight and water, there would be more than one cause that resulted in the larger plant.

The color of flowers can also be affected by the environment.

Hydrangea flowers are sensitive to acid and other chemicals in soil.

When the soil contains a lot of acid, the flowers are blue. In soil that is not acidic, the flowers are pink. A gardener can affect the color of the flowers by adding certain chemicals to the soil.

Environmental factors can also enhance the survival of an organism. Plants growing in soil that is rich in nutrients usually grow taller, have more flowers, and are generally healthier. Suppose two groups of identical plants receive the same amounts of light and water, but one group also receives fertilizer that contains nutrients it needs.

The plant grown with fertilizer will often be taller, have more flowers, and is more likely to survive than the plant without fertilizer.

Day length also influences the production of flowers in plants. Some species of plants, such as chrysanthemums, produce flowers only when there are fewer than 12 hours of daylight, so they bloom in spring or autumn. Other plant species flower only when there are more than 12 hours of daylight. These include most summer-flowering plants, including California poppies, dill, and spinach.

Figure 5B Plants grown in soil with fertilizer usually grow taller, have more flowers, and are generally healthier. Fertilizer is an environmental factor that can affect a plant’s physical traits.

Plant Physical Traits and Their Environment

Soil With Fertilizer

Soil Without Fertilizer

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6. Passing on Traits to Offspring

This mother bear’s thick fur and ability to find water has helped her survive to adulthood. Individuals with traits that help them survive in their environment are the ones that will reproduce. Since some traits can be passed on from parent to offspring, her offspring will also have some of the physical and behavioral traits that helped her survive.

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You have read about many physical and behavioral traits that plants and animals have that can increase their chance of survival. How do they get these traits?

Many physical traits are passed from parents to offspring. Look at the mother brown bear and her cubs. Notice their thick fur. Notice, too, that each bear has a hump of muscles on its shoulders. Thick brown fur and a shoulder hump are physical traits that are passed from parents to offspring. Many physical traits that aid in survival are passed from parent to offspring, such as the gills of a fish that remove air from water or the thorns on a plant that prevent an animal from eating it.

Even behavioral traits can be passed on to offspring. For example, many different species of spiders spin webs with unique designs. Some webs look like bike wheels. Others are rectangular and flat like sheets.

Still others are spiral-shaped. A spider is hatched knowing how to spin the appropriate kind of web for its species. The offspring spins the same kind of web as its parents because this behavior is passed on from the parents to the offspring.

Other behavioral traits are passed on when the offspring learns behaviors from the parent. For example, the mother bear in the photo is teaching its offspring how to hunt for fish so that they do not starve.

Lions also have to learn to hunt from their mothers. Although the cub knows that it is supposed to kill prey, it does not know how to stalk a zebra, how to work with other lions in the group to ambush the zebra, how to pick out the weak members of the zebra herd, or which parts of the zebra to attack. Cubs learn all these skills by watching their mothers and other females in the group hunt. By the time the cub is an adult, it should be very good at hunting and the females will be able to teach their own cubs to hunt.

Only organisms which survive long enough to reproduce pass their traits on to their offspring. For example, a bear with especially thick fur is more likely to survive a cold winter than a bear with fur that is less thick. The bear with thinner fur might freeze to death while the bear with thicker fur is more likely to survive long enough to reproduce and have offspring.

Additionally, cubs born of this parent might also have very thick fur, since this trait can be passed on from parent to offspring. If the offspring get this trait, it will also help them survive better in cold winters. The ability to combat cold temperatures might allow them to also survive long enough to reproduce and have cubs themselves. In this way, traits that help an organism survive can be passed on through many generations.

LESSON SUMMARY

Traits for Survival Organisms’ Survival In order to survive, organisms must meet their needs and avoid threats in their environment. Organisms acquire energy and materials from their environment to meet their needs.

Dehydration, disease, starvation, extreme temperatures, and predation are a few factors that threaten an organism’s survival.

Physical Traits and Survival Both plants and animals use physical traits to help them meet their needs and protect them from threats to their survival. Physical traits are distinct structures or body parts of an organism.

Traits Inspire Design Engineers have used their knowledge of an animal’s traits, like feathers for keeping warm, as inspiration for solutions to human problems, like surviving in cold weather. Criteria are the requirements that have to be met for a successful design. Constraints are limitations that need to be kept in mind when working on an engineering solution. Artificial down feathers were developed to meet the criteria and constraints for new jackets for the U.S. Army.

Behavioral Traits and Survival Behaving in a certain way may help an animal meet its needs or survive a threat. It can survive these threats by either avoiding danger or escaping from it. Behavioral traits are distinct ways in which an organism interacts with its environment.

Environmental Influences on Traits Environmental factors can influence an organism’s traits. Often there is more than one cause, or environmental factor, that can have an effect on an organism’s traits.

Passing on Traits to Offspring Offspring from parents that were able to survive and reproduce have some of the same traits that allowed the parent to survive. This is because certain physical and behavioral traits were passed on from parent to offspring. Traits that help an organism survive can sometimes be passed on through many generations.

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Traits for Reproduction What physical and behavioral traits help organisms reproduce?

Introduction

Vocabulary

Dusky leaf monkeys live in the treetops of rainforests in Thailand, Myanmar, and Malaysia. Like human babies, this baby monkey cannot take care of itself. It mostly clings to its mother’s fur and drinks the milk that her body provides. As the monkey grows, it will develop other traits for survival; it will develop teeth and a mature digestive system that can get energy and nutrients from leaves. Until then, its mother will clean, feed, and protect her baby. Why does the mother take care of its baby when doing so does not help her own survival?

You learned that traits for survival help an organism meet its needs in its environment. In this lesson, you will learn about traits for reproduction. These are physical or behavioral traits that help an organism find a mate and reproduce or help it to take care of its offspring. First, you will explore how animals’ reproductive traits increase the chance of producing offspring that survive. Next, you will learn how a group of wildlife biologists used their understanding of the reproductive traits of California condors and the engineering process to help save this endangered species. You will also find out how plants’ reproductive traits produce a new generation of plants.

As you read, think about the cause and effect relationships between the reproductive traits and the survival of offspring. For example, how does the behavior of dusky leaf monkey mothers relate to future generations of dusky leaf monkeys?

reproduction the process by which an organism makes more organisms of the same species courtship behavior a way of acting that will help an animal attract a mate model a representation of something in the real world which makes important aspects easier to observe and hides unimportant aspects germinate to begin the growth of a new plant from a seed

Next Generation Science Standards Performance Expectations MS-LS1-4. Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.

MS-ETS1-4. Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process such that an optimal design can be achieved.

Science and Engineering Practices Engaging in Argument from Evidence Use an oral and written argument supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon or a solution to a problem.

Developing and Using Models Develop a model to generate data to test ideas about designed systems, including those representing inputs and outputs.

Crosscutting Concepts Cause and Effect Phenomena may have more than one cause, and some cause and effect relationships in systems can only be described using probability.

Disciplinary Core Ideas LS1.B. • Animals engage in characteristic behaviors that increase the odds of reproduction. • Plants reproduce in a variety of ways, sometimes depending on animal behavior and specialized features for reproduction.

ETS1.B. • A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. • Models of all kinds are important for testing solutions.

ETS1.C. The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

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1. Animal Physical Traits for Reproduction

A male peafowl, known as a peacock, has a large and colorful tail. This tail is a physical reproductive trait that increases the chance that the male will attract a female mate.

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Have you ever seen a picture of a male peafowl, known as a peacock, with its large and colorful tail? What about a female kangaroo with its young joey in its pouch? What do a peacock’s tail and a kangaroo’s pouch have in common? They are both physical traits. But unlike physical traits for survival of the peacock or the kangaroo, they are physical traits that help these organisms have or take care of their offspring.

Reproduction is the process by which an organism makes more organisms of the same species. If organisms did not reproduce, their species would die out and become extinct. Reproductive traits increase the chance, or probability, that an organism will find a mate for reproduction or have offspring that survive. A peacock’s tail and a kangaroo’s pouch are examples of physical reproductive traits.

These traits do not guarantee that an organism will reproduce or have offspring that survive, but they increase the odds that this will happen.

2. Animal Behavioral Traits for Reproduction Like traits for survival, there are both physical and behavioral reproductive traits. Peacocks do not just have large colorful tails, they also strut around and shake their rear feathers to attract the females’ attention. In a group of peacocks, how does one male stand out as a better mate than the other males?

Many animal species have reproductive traits that help them to find or attract a potential mate. Peacocks who are better at attracting the attention of the female by fanning out their large tail and strutting around are more likely to reproduce. Any behavior or way of acting that helps an animal attract a mate is called a courtship behavior. There are different kinds of courtship behaviors. Keep in mind how each is part of a cause and effect relationship, a relationship between two events in which one influences the other. The behavior is the cause and the effect is how likely the organism will get a mate.

Have you ever seen fireflies flashing at night? One type of courtship behavior is flashing signals, like lights. There are many species of fireflies, and they generally cannot mate with each other. Fireflies have a structure in their abdomen that produces light. Each species of firefly flashes its light in a specific pattern. When a male flashes its particular pattern, typically a female of the same species that is ready to mate will flash back in the same pattern to tell the male where she is. Females of other firefly species generally do not respond. This helps to ensure that they do not try to mate with a male that cannot result in offspring.

Males of each species of firefly flash a specific light pattern to attract a female of the same species. This signal is a type of courtship behavior for the male and female fireflies to find each other and reproduce.

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This moose’s large antlers are a physical reproductive trait. The large antlers indicate to a female that the male is strong and healthy. Impressing a female increases the chance that he will reproduce.

A satin bowerbird decorates his area with blue objects and dances with them to attract a female. This is a type of courtship behavior—a behavioral reproductive trait that increases the probability that this bird will attract a female to mate with.

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Releasing chemicals and sounds can also be examples of courtship behaviors. Many species of animals release chemicals from their body as a way to attract a mate. The chemicals act like perfume to attract an animal of the same species. Sounds, too, can attract potential mates.

Birds sing, frogs croak, and koalas bellow. Often, the male makes the mating sounds. Individuals of other species do not respond.

Fighting is another type of courtship behavior. Sometimes the males of a species have to fight other males of that species to win a mate. Male lions, gorillas, deer, and moose all fight for potential mates. Large antlers help male deer and moose drive away or kill their rivals. The strongest and healthiest male usually wins the fight, so he wins the chance to mate and produce offspring. Strength, size, and antler size all indicate to a female that a male is healthy and will pass these traits to his offspring.

A courtship behavior is often very complex. Some animals dance or create art as a form of courtship behavior. Male bowerbirds build elaborate nests, called bowers. They collect bits of glass, feathers, flower petals, or even bits of plastic and ribbons, from the environment to decorate the bower. Each species of bowerbird builds a bower of a unique shape and collects specific colorful items, often preferring a single color.

When a female approaches, he picks up an item in his beak and dances with it to attract her. She will mate with the male that does the best dance and has the most impressive display of objects around its elaborate nest.

Courtship behaviors and other reproductive traits do not guarantee that an individual will find and recognize a potential mate. They do not guarantee that the individual will produce offspring. However, they increase the probability that this will happen. Thus, these reproductive strategies help the species survive in the future.

3. Improving Chances of Animal Offspring Survival Organisms can go through great efforts to find a mate and reproduce. With all the effort, how can an organism increase the probability that its offspring survive the threats in the environment?

There are different approaches organisms can take to increase the chance that the greatest number of their offspring survive. One approach is to have lots of offspring. For example, a female sea turtle lays hundreds of eggs on a beach during her lifetime because fewer than 1 in 1,000 of her offspring will survive to grow up and reproduce.

Mother sea turtles do not take care of their eggs or offspring, so when sea turtle babies hatch, they crawl into the sea on their own. Many eggs never hatch, and some baby turtles are eaten on their way to the sea. Or, once in the water they could be eaten by large fish and other marine animals. Some animal species, like the sea turtle, do not care for their young, so they rely on laying many eggs to increase the probability that some of the offspring will survive.

Another approach is for an organism to have fewer offspring, but to take care of them. In these cases, the odds that each of the offspring will survive is much greater. Species that do this have traits that help them care for their young. For example, musk oxen are large animals that live in the arctic tundra. Females have one baby at a time, so it gets lots of care. The mother feeds her baby with her milk. To stay warm, the baby rests against its mother’s long hair. When musk oxen sense danger, the adults in the herd form a circle around the young to protect them, ready to fight off predators that attack young animals.

Musk oxen adults form a circle around their young to protect them from predators. By facing outward, the adults form a solid wall that often discourages a predator from attacking.

Taking care of offspring is a type of behavioral reproductive trait.

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Engineering Design

4. Designing Processes for Condor Recovery Sometimes scientists get involved to help the offspring of a species survive. In 1982, there were only 22 California condors, a type of vulture, living in the wild. California condors were dying, and scientists realized that if they did not design solutions to help them increase their numbers, this species would become extinct.

The criterion (the singular form of criteria) that the scientists wanted to meet was to eventually have a self-sustaining wild population of condors. A self-sustaining population would reproduce and continue to survive without further human help.

Designing Solutions for Condor Reproduction Since condors were not reproducing enough for the species to survive, scientists decided to capture every condor in the wild and try to get them to produce more offspring in captivity. One large constraint the scientists faced is that condors only lay one egg a year. However, they discovered that if you remove the egg before it hatches, the mother condor will lay a new egg. This improved the growth of the population because the condors laid twice as many eggs this way. The eggs were put in warming incubators until they hatched. Then, the baby condors were raised in zoos until they were old enough to survive on their own.

Designing Solutions for Condor Survival Unfortunately, the condors released from the zoos were still dying. These captive bred condors did not know how to handle the dangers of their natural wild environment. To teach the condors to avoid dangers in their environment, the scientists designed a zoo habitat as a model for the condor’s natural environment. Models are representations of something in the real world which make important aspects easier to observe and hide unimportant aspects.

To help California condors, scientists learned how to raise baby condors in zoos for later release. They designed processes for how to get mother condors to lay more eggs, which helped increase the number of condors. This was an important step to meet the criterion of creating a selfsustaining group of condors.

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The scientists improved upon the model habitat as they learned more about how to help the condors survive. For example, a few of the initially released condors had died because they were killed by humans or human activities. The scientists’ solution was to improve the model by helping condors recognize and associate with other condors, but learn to avoid humans. They did this by modeling condor mothers using puppets that looked like adult condors. They used the puppets to feed and take care of the baby condors. This helped the condors to associate good things, like being fed, with other condors and not humans. When humans did interact with the condors, they would first try to scare them so that they would fly away from humans instead of towards them. This trained the condors to stay away from areas with more humans where they were more likely to be killed.

Even after this change, condors were dying when they were released into the wild. Some condors died or were hurt by running into power lines. To improve the process of raising condors that would survive, scientists added dangers like fake power lines into the zoo habitat model. The young condors learned to avoid power lines because they would receive a small shock when they got too close.

Finally, when condors were old enough, scientists brought an older adult condor into the habitat. The older condor helped the younger condor learn to behave and avoid dangers.

Over time, the habitat became a good enough model of the outside environment that many young condors released from the zoo could survive on their own in the wild. The solutions for helping the California condors reproduce and survive were tested and modified over many years but resulted in a group of wild condors that seems to be self-sustaining.

This condor was raised in captivity in a habitat that modeled the outside environment. Its wings are tagged so that scientists can track its survival.

If this condor dies, they can use the information about how it dies to improve the model and the training for the condors in captivity.

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Traits like the bright orange structure of these purple crocus flowers lead insects directly to the pollen. Many insects are attracted to the contrast between the orange and purple.

Since animals like insects can move between flowers, attracting insects to pick up and transfer pollen is a helpful reproductive trait for plants.

5. Plant Traits for Reproduction Not only do flowers brighten up our environment with their vibrant colors and sweet odors, but they are a vital part of plant reproduction.

Like animals, plants have traits that increase the probability that they will reproduce and have surviving offspring. How do you think traits such as bright colors and sweet odors help do this?

Plants have traits, like sweet nectar, that attract insects. This bee was attracted to the flower. Now that the plant’s pollen has rubbed off the flower onto the bee’s body, the pollen can be transferred to another flower that the bee visits, which could help this plant reproduce.

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Traits for Reproducing Plants do not seem to show courtship behavior like animals, but they do have physical traits that aid reproduction. Pollen is a structure that many species of plants use for reproduction. The male part of a flower produces pollen. The small size of pollen is a physical trait that allows it to get trapped onto animals’ bodies or get carried in the wind. When pollen reaches the female part of a flower, a seed can form. Seeds are the offspring of a plant that can develop into a new adult plant.

Flowers are also reproductive structures. Some flowers have colored markings that lead insects to the structures that contain pollen. Plants use animals to increase the probability of reproducing. The sweet odors, the nectar, and the colored markings are physical traits of flowers that attract insects. Insects such as bees and butterflies visit flowers to collect the sweet nectar they feed on. As an insect pokes its head into a flower to sip the nectar, some of the flower’s pollen rubs off onto the insect’s body. When the insect visits another flower of the same species, the pollen on its body is carried to the female part of that flower allowing a seed to form. So, when animals transfer pollen, the plant is using the behavior of the animal for its own reproduction.

Some kinds of plants, such as pine and spruce trees, do not have flowers. These plants produce pollen in cones instead of flowers. Pine tree pollen has different physical reproductive traits. The pine trees rely on wind to pick up their pollen instead of insects. Pine tree pollen has “wings,” so it floats on wind. The wings keep the pollen in the air so that it can travel away from the parent plant and hopefully land on a female pine cone, where it can form a seed.

Traits for Offspring Survival For the offspring’s best chance of survival, the seeds formed inside flowers must be scattered to a location where they can germinate without competing with the parent plant for light, water, space, and nutrients. To germinate is to begin the growth of a new plant from a seed. Because seeds cannot move on their own, plants have many different traits that aid in seed dispersal.

Seeds can be dispersed by wind, water, and animals. Seeds that are dispersed by wind often have structures similar to parachutes. Seeds with parachutes stay in the air longer and are carried farther away from the parent plant. You may have blown such fluffy parachutes off of a dandelion stem. Plants that grow near water, such as coconut palm trees, produce large seeds that can float when they’re inside a coconut fruit. The water carries the fruit and the seeds inside to new locations where they can germinate and grow. Seeds can also be dispersed by animals. Burdock plants have seeds with hooks that easily get caught in the fur of passing animals. Eventually, the seed falls off the fur, often far away from the parent.

If conditions are right for growth where a seed lands, it will germinate and grow into a new generation of plant. But not all seeds will germinate. Many land on poor or dry soil, where there may not be enough light for plant growth. Some seeds are eaten by animals before they have the chance to germinate. Plant seeds have traits that help prevent them from being eaten. For example, nuts are large seeds that have hard shells. Although some of these seeds will be eaten if the shell is removed, the hard shell increases the probability that the seed will survive long enough to germinate.

Another way to increase the probability that some seeds will germinate is to produce more seeds. The more seeds a plant species can produce, the better the chance that at least some of the plant’s offspring will survive. Plants of some species produce many seeds. For example, a birch tree can produce up to 35 million seeds per acre.

Burdock seeds have hooks that get caught in the fur of animals and are carried long distances from the parent plant. These hooks are physical reproductive traits that help the offspring survive. Because they are carried far away, the seeds can germinate without competing for resources with the parent plant.

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Key Science Concept

Traits, Mates, and Offspring Reproductive traits can both increase the probability of attracting a mate for reproduction and increase the chance that an offspring will survive. Both plants and animals have these reproductive traits. These are examples of plant and animal reproductive traits.

Calling for Mates For most species of frogs, only the male can croak. The frog’s ability to croak comes from blowing up a large sac of air in its neck. The type of croak will attract female frogs. The croak is an example of a behavioral reproductive trait that increases the probability of attracting a mate.

Dispersing Seeds Tumbleweeds are parts of a plant that break off and catch the wind. The seeds fall off as the tumbleweed rolls against the ground. Seeds that germinate far from the parent may have more space and nutrients to grow and a better chance of survival.

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Flashy Color Male mandrills are more colorful and are much larger than the females. The most colorful males have a greater probability of attracting the most females to reproduce with. The male mandrill’s colorful fur is an example of a physical reproductive trait.

Animal Carriers Horses graze for food in long grasses and can get burrs stuck in their manes, which they will carry until the burrs fall off the horse. These hooked burrs hold the seeds to the plant. Plants that produce burrs are using animal behavioral traits to increase the chance that their seeds will germinate far from the parent plant and survive.

6. Passing on Reproductive Traits You have read that male bowerbirds do elaborate mating dances to attract females. Male peacock spiders also dance. They stick up their colorful abdomen and wave their hind legs around. This dance attracts the female peacock spiders to reproduce with them. How does the bower bird or spider know how to do its dance?

Many physical and behavioral traits that lead to reproduction or to care of offspring are passed on from parent to offspring. This is very similar to the way traits that help individuals survive are passed on.

Organisms that survive and attract mates have useful traits that make them more likely to reproduce. Many of those traits can be passed on from parent to offspring, even behavioral traits like a mating dance.

If the offspring gets this trait and also survives, it too is more likely to attract a mate and reproduce. In this way, a reproductive trait that helps an organism find a mate or take care of its offspring can be passed on from parent to offspring for many generations.

This peacock spider displays its colorful back and dances around with its hind legs to attract a female. Only males with the best dance and most colorful back will attract a female as a mate. These physical and behavioral traits can be passed to their offspring.

LESSON SUMMARY

Traits for Reproduction Physical Traits for Reproduction Physical reproductive traits increase the probability that an individual will get a mate and produce offspring that survive.

Behavioral Traits for Reproduction Many animals have behavioral reproductive traits that help them find a mate and reproduce. Like physical traits, behavioral reproductive traits increase the probability that an individual will get a mate and produce surviving offspring.

Improving Chances of Animal Offspring Survival Some species of animals provide care for their young to help them survive. Other animals produce large numbers of offspring to increase the chance that some will survive. Animal species that care for their young do not have to produce as many offspring because the ones that are taken care of are more likely to survive.

Designing Processes for Condor Recovery Scientists used engineering processes to help endangered California condors reproduce and survive. These processes improved over time as the scientists gained more information about how to help condors survive.

Plant Traits for Reproduction Plants have structures like pollen, flowers, and seeds that support plant reproduction. These structures have different physical traits to help the plant reproduce by attracting animals or by reaching a location where they can germinate.

Passing On Reproductive Traits Many physical and behavioral traits that lead to reproduction or to care of offspring are passed on from parent to offspring. These traits can even help their offspring do the same if they are passed on.

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Bodies

ANCHORING PHENOMENON People become sick when body systems don’t function properly.

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Phenomenon-Based Storyline Every day, people all over the world get sick. Sometimes they recover; sometimes they don’t. Like a doctor, use evidence from medical charts, test results, and medical fact sheets to “diagnose” four patients.

Next Generation Science Standards Performance Expectations MS-LS1-3.

Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

MS-LS1-8.

Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.

Science and Engineering Practices Engaging in Argument from Evidence Use an oral and written argument supported by evidence to support or refute an explanation or a model for a phenomenon.

Obtaining, Evaluating, and Communicating Information Gather, read, and synthesize information from multiple appropriate sources and assess the credibility, accuracy, and possible bias of each publication and methods used, and describe how they are supported or not supported by evidence.

Crosscutting Concepts

Disciplinary Core Ideas

Systems and System Models Systems may interact with other systems; they may have sub-systems and be a part of larger complex systems.

LS1.A. Structure and Function In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions.

Cause and Effect Cause and effect relationships may be used to predict phenomena in natural systems.

Science Is a Human Endeavor Scientists and engineers are guided by habits of mind such as intellectual honesty, tolerance of ambiguity.

LS1.D. Information Processing Each sense receptor responds to different inputs (electromagnetic, mechanical, chemical), transmitting them as signals that travel along nerve cells to the brain. The signals are then processed in the brain, resulting in immediate behaviors or memories.

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Interacting Body Systems How do your body systems work together?

Introduction Suppose you are on a team that is building a robot. You can think of the robot as a system and each part of the robot as a subsystem. The pieces that make up the structure of the robot are one subsystem. The wires that send signals to make the robot move are another subsystem.

The remote control that you use to control the robot’s movements is another subsystem. No single subsystem can make the robot perform all its functions, but it can function if all the subsystems work together.

How is the robot, and all its interacting parts, like a human being?

Like the robot, the human body is a system made up of interacting subsystems that allow it to function. Each part of the human body is part of subsystem called a body system. Each of these body systems performs a certain function for the body. Look at the runner’s heart, blood vessels, and bones. His heart pumps blood through blood vessels and delivers oxygen and nutrients to all parts of his body. His lungs take in oxygen that helps to supply energy to his muscles. Bones that connect to muscles enable him to move. To what body systems do these parts belong? How do you think they interact? What do you think would happen if one of these parts was not working properly?

In this lesson, you will learn how parts of the body work together to allow a person to function and move using the example of a person running. You will begin to learn about the subsystems that make up an organism’s body. These body systems exist in humans and many other animals and plants. Finally, you will learn how scientists can use other organisms’ body systems to model human body systems.

Vocabulary skeletal system a body system made up of the framework of bones that supports an organism’s body, protects its internal structures, and allows the body to move muscular system a body system made up of all the muscles of the body that cause movement when they contract, or shorten organ a typically self-contained structure that carries out a particular function for the body digestive system the body system made up of organs that break down food into substances that can be absorbed and used for energy and gets rid of the remaining solid waste that cannot be absorbed respiratory system the body system made up of the organs that bring oxygen into the body and remove carbon dioxide waste circulatory system the body system made up of the heart and blood vessels that circulate blood through the body excretory system the body system made up of the organs that get rid of waste reproductive system the body system made up of the organs that allow adults to produce offspring

Next Generation Science Standards Performance Expectations MS-LS1-3. Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

Science and Engineering Practices Engaging in Argument from Evidence Use an oral and written argument supported by evidence

to support or refute an explanation or a model for a phenomenon.

Crosscutting Concepts Systems and System Models Systems may interact with other systems; they may have subsystems and be a part of larger complex systems.

Science is a Human Endeavor

Disciplinary Core Ideas LS1.A. In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions.

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1. The Skeletal and Muscular Systems

Figure 1A The skeletal system is made up of all the bones in the body. The muscular system is made up of all the muscles in the body. The two systems work together to move the body.

For most of human history, people have had to hunt for meat and search for edible plants to meet their needs for food. Hunting often required running after prey or hiding in trees and carefully throwing weapons at prey as they try to run away. How does the human body allow a person to run, stand, hide, and throw?

The skeletal system is an important body system for allowing a person to move. The skeletal system is the framework of bones that supports an organism’s body, protects its internal structures, and allows the body to move. This framework gives the body its overall structure and general shape. The structures that connect bones with other bones are called ligaments. Some bones, such as the skull and ribs, protect soft internal organs. The skull protects the brain, and the ribs form a cage that protects the heart and lungs. Other bones interact with muscles to cause movement.

The muscular system is also important for allowing a person to move. All the muscles of the body make up the muscular system.

Muscles cause movement when they contract, or shorten. Muscles connect to bones with structures called tendons. Not all muscles are for moving the skeleton, though. The heart is part of the muscular system because it, too, is made of muscle. The heart muscle contracting is what causes the heart to beat. Other muscles in the muscular system help move food or blood through the body.

The Skeletal and Muscular Systems Work Together

Skeletal System

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Muscular System

Bones Move by Muscle Contraction Contracting Biceps

Contracting Triceps

Figure 1B Muscles and bones work together to allow for movement, like when picking up an object. When the biceps muscle contracts, the triceps muscle relaxes and the arm bends at the elbow. When the triceps muscle contracts and shortens, the biceps relaxes and the arm straightens at the elbow.

The skeletal and muscular systems are examples of body systems.

A body system is a group of organs that works together to perform a particular function in the body. An organ is a typically self-contained structure that carries out a particular function for the body. A bone is an organ of the skeletal system. Tendons and ligaments are other organs in the skeletal system. The brain, heart, and stomach are examples of organs in other body systems. No single organ can do the job of an entire body system.

The skeletal and muscular systems work together to help a person move. As an example, Figure 1B shows how the biceps and triceps muscles in the upper arm move bones in the arm to bend at the elbow, like when you want to pick up an object. The biceps and triceps are attached to bones in the arm and shoulder by tendons. Starting with a straight arm, when the biceps muscle contracts, it pulls on the bones it is connected to. At the same time, the triceps relax so that the bone is not pulled in two directions at once. Since the lower part of the arm and the upper part of the arm are connected by a hinge, like a door, the lower part of the arm swings up. To straighten the arm at the elbow, the triceps will contract and the biceps relax. Many muscles attached to bones work in pairs like this to move the bones one direction or another.

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2. The Digestive System

Food, like this cheeseburger, provides the body with energy for growth, repair, and life processes. But first, the hamburger must be broken down by the organs in the digestive system into nutrients that the body can use. In the mouth, the large carbohydrates in the bun will be broken down into sugars by chemical digestion.

Most people no longer hunt for their food, but humans still need to eat multiple times a day. All animals need food to survive. Food gives a person energy to run, throw, move, and even sleep. An organism’s body runs on the energy stored in food. How does the body get energy from food?

The body cannot directly use the energy found in food. To be used by the body, food must first be broken down, or digested, into simpler substances. The digestive system is the body system that breaks down food into substances that can be absorbed and used for energy and gets rid of the remaining solid waste that cannot be absorbed. Food is mostly made up of substances called carbohydrates, proteins, and fats.

These are broken up into simpler substances that can be absorbed and used throughout the body for energy.

The digestive system forms a long tube from the mouth to the rectum. Hollow, muscular organs make up different parts of the tube.

The main organs of the digestive system are the mouth, esophagus, stomach, small intestine, large intestine, and rectum. Each one has an important role in digesting food.

The Mouth and Esophagus Digestion occurs in the mouth in two different ways. Large food particles are split into smaller pieces by chewing, grinding, and mashing with the teeth.

Food is also broken down chemically by digestive juices in the saliva.

Chemical digestion changes the food into different substances through chemical reactions. Saliva specifically breaks down large carbohydrates into simpler sugars.

Say, for example, you are eating a hamburger. Your teeth break up the pieces of the bun, meat, lettuce, and tomato. Your saliva breaks down the carbohydrates in the bun into sugars.

Your tongue helps by moving the food around in the mouth and then pushing it into the throat. Swallowing moves the food into the next organ, the esophagus.

The esophagus is the part of the digestive tube that connects the mouth to the stomach. Muscles in the esophagus push the food into the stomach.

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The Stomach The stomach is a bag-like organ made of strong muscles. As the muscles in the stomach contract and relax, food is mixed and broken down.

When the food is in smaller pieces, it is easier to digest. Here, all the pieces of your hamburger are being broken apart.

Additionally, several digestive juices made in the stomach chemically digest proteins in the hamburger. From the stomach, the partially digested food moves into the small intestine.

Parts of the Digestive System

Mouth Esophagus

The Intestines and Solid Organs The small intestine is the longest organ of Liver the digestive system, measuring more than six meters long in humans. Most of the digestion of proteins and carbohydrates takes place here. The small intestine Small Intestine absorbs most of the digested nutrients Large Intestine that have been broken down and transfers those nutrients to the blood stream. Blood transports the nutrients to all parts of the body, where the energy stored in the nutrients is released.

There are two organs that are not part of the hollow tube that makes up most of the digestive system, but they help in digestion by making digestive juices flow into the small intestine.

The liver produces digestive juices that break down fats, like the fat in the hamburger meat. The pancreas produces digestive juices that continue to break down fats, carbohydrates, and proteins into even smaller substances.

Material that has not been absorbed in the small intestine passes into the large intestine. Here, water is removed. Most of what remains is waste. Waste is stored in the lower part of the large intestine, called the rectum, before it is eliminated from the body.

The trip your hamburger has made through your digestive system has lasted many hours and involved the interaction of many organs and systems. The digestive system breaks down food and the other organ systems transport this digested food to be used for energy all over the body. The muscles in the digestive system move food all the way through the tube, from the mouth to the rectum. Without the aid of muscles, blood, and other parts of the body, the digestive system would not be able to provide energy to the body.

Stomach

Rectum

Figure 2 The digestive system forms a long hollow tube from the mouth to the rectum. Different organs with different functions make up the parts of the tube, but they all work together to create a functional digestive system.

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3. The Respiratory and Circulatory Systems You probably don’t pay much attention to the breaths you take every day or whether your heart is beating. If you are a runner, however, you may have noticed that your heart beats faster and you begin to breathe more rapidly when you start to run. Why does this happen?

The Respiratory System When you are running, you start breathing rapidly to take in more oxygen, and push out more carbon dioxide. Your body requires oxygen for the process of releasing energy from broken down food. Running uses a lot of energy, so more oxygen Figure 3 is needed. During these chemical reactions, carbon dioxide waste is The main organs of the respiratory formed. Too much carbon dioxide is toxic, so it must be removed from system are the lungs. The circulatory the body before it can cause harm. This causes you to breathe out more system is made up of the heart and to release that carbon dioxide. the blood vessels. Together these two The respiratory system is the body system that brings oxygen into systems transport blood, oxygen, and the body and removes carbon dioxide waste. The main organs of the nutrients throughout the body. Oxygen respiratory system are a pair of lungs. When you inhale, air containing helps to release energy from broken oxygen passes from the environment through your nose and mouth down food, which is essential for and into your lungs through tubes. At the end of the tubes, deep within running or even just surviving. the lungs, are many tiny air sacs that have very thin walls. Oxygen entering the lungs The Respiratory and Circulatory Systems passes from the tubes and through the walls of the air sacs. Here is where the respiratory Heart system interacts with the circulatory system.

Trachea

Lungs Blood Vessels

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The Circulatory System As you run, your heart begins to beat faster. The oxygen that was in your lungs moves into your blood, where it is carried all over the body.

The circulatory system, consisting of the heart and blood vessels, circulates blood throughout the body. The pumping action of the heart muscle is what moves the blood all around the body. Oxygenated blood near the lungs gets to the heart through a vein, a type of blood vessel. Veins carry blood to the heart from the rest of the body. The heart then pumps that blood all over the body through arteries, another type of blood vessel. Arteries carry blood away from the heart. As you run, your heart beats faster to pick up more oxygen from the lungs and transport it to where it is needed. In addition to oxygen, blood can transport nutrients and waste from all over the body to where it can be used or removed.

4. The Excretory System

Parts of the Urinary System If you have ever breathed out on a cold Kidney Kidney day, you have observed evidence that your breath contains water vapor. When you exhale you are breathing out wastes, like excess water and carbon dioxide. If you were running, what other ways do you think you might be getting rid of waste from your body?

There are different ways that the body gets rid of waste. In addition to breathing out, you might get rid of some waste by sweating, especially when you’re doing a rigorous activity like running. Most of the body’s liquid waste is removed in the form of urine.

Interestingly, you are less likely to need to urinate when running because much of the excess water in your body will be released through sweat instead of urine.

The excretory system is the body system that gets rid of wastes. Not everything can be organized into clear distinct units in science, and biologists have to accept some amount of Bladder ambiguity, or inexactness, in making a distinction between body systems. For example, some of the organs of the excretory system also belong to other body systems. As you have already learned, the Figure 4 digestive system also eliminates waste after the nutrients from digestion The urinary system is part of the are absorbed, so the large intestine, including the rectum, is part of both excretory system. Kidneys filter and the digestive and excretory systems. The lungs are part of the excretory remove waste and excess water from system as well as the respiratory system. They function to take in oxygen, blood. The bladder stores this excess but they also get rid of gas wastes such as water vapor and carbon dioxide. water as urine until it is excreted.

In addition to getting rid of waste, one of the important functions Other parts of the excretory system of the excretory system is to regulate the amount of water in the body. remove water vapor, carbon dioxide, The urinary system, which is part of the excretory system, helps to and solid wastes from foods. get rid of liquid waste by filtering the blood, as well as regulating the amount of water in the body. The major organs of the urinary system are the kidneys and the bladder. As blood flows through the kidneys, they filter out most of the materials that are dissolved in the blood.

Some of the materials, such as nutrients and water, are returned to the blood, but wastes are not. The kidneys keep the amount of water in the body constant by controlling how much water is returned to the blood.

The cleansed blood returns to the heart through veins. The excess water and wastes travel to the bladder, a hollow bag made of muscle that stores the wastes as urine. A tube at the bottom of the bladder carries the urine out of the body.

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Interaction Between the Respiratory and Circulatory Systems To body

To body

From body From body

To lungs To lungs

From lungs

From lungs

Heart

Lung

Lung From body

To body

5. Systems Work Together Figure 5 Body systems, like the respiratory and circulatory system, interact to fulfill the needs of the body. In this example, oxygen-poor blood is pumped by the heart into the lungs, where oxygen is added. The blood then travels back to the heart, which pumps the oxygenrich blood to the rest of the body.

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Each body system plays an important role when you run, but no one system on its own can make you run. What makes it possible for your body to run, jump, throw, and even survive?

All the body systems have to interact to make a functional body.

You have learned that to run, the body uses muscles to move bones.

Because muscles need energy, a runner needs to eat food, which is broken up into nutrients by the digestive system. The nutrients are carried from the digestive systems to the muscles using the circulatory system. In the muscles, energy is released from the nutrients in chemical reactions that use oxygen. Oxygen is delivered to the muscles by the respiratory and circulatory systems. The lungs take in oxygen from the air, where it is transferred to the blood. The heart muscle contracts to pump that oxygen-rich blood to the whole body. While traveling through the body, the blood picks up waste, like carbon dioxide, and brings it to the organs of the excretory system, like the lungs, where it can be removed from the body.

Even for a runner to just breathe in and out requires the muscular and skeletal systems working with the respiratory system. The diaphragm is a large flat muscle that stretches below the lungs. When the diaphragm contracts, the ribs move outward, enlarging the chest cavity. This motion pulls air into the lungs. To exhale, the diaphragm relaxes and the ribs move inward. The smaller chest cavity forces the lungs to push air out of the body. These are just some examples of how the body functions through the interactions of the body systems.

Key Science Concept

Interactions Among Body Systems Many interactions between the body systems take place in a person’s body. To run, people must move their legs and arms to push their body forward. As they do this, their heart starts to speed up and they breathe more quickly. They are using up energy and losing water as they begin to sweat. Here are just a few examples of how their body systems are working together to make all these things occur.

Circulatory and Excretory The runner’s excretory system removes wastes through the runner’s skin, large intestine, and lungs. Many of these waste products are transported to the excretory system through the circulatory system.

Muscular and Skeletal The muscular system works with the skeletal system. Muscles are attached to bones. When the muscles in the runner’s leg contract, the bones in the leg move to a new position and the leg bends.

Respiratory and Circulatory The respiratory system works with the circulatory system to take in oxygen from the environment and carry it to all parts of the runner’s body through a network of blood vessels.

Circulatory and Digestive The circulatory system works with the digestive system to transport nutrients to all parts of the runner’s body. Nutrients are produced when food is digested.

Circulatory and Muscular In this runner’s legs, the circulatory system is interacting with the muscular system.

Energy-rich nutrients and oxygen dissolved in the blood travel through arteries to the muscles.

Energy and oxygen allow the muscles to work.

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6. The Reproductive System You have learned that organisms produce offspring. What body systems are needed to produce offspring?

Humans, as well as all other organisms, use a reproductive system to produce offspring. The reproductive system is the body system that allows adults to produce offspring. Unlike most other body systems, the reproductive system is not fully functional as soon as you are born. It must first mature, a process that usually occurs in your teen years. Also unlike other body systems, the male and female reproductive systems are different. However, both make small specialized reproductive structures. The male system produces sperm. The female reproductive system produces eggs. Both kinds of structures contain information needed to create a new organism.

The Male Reproductive System The main organs of the male reproductive system are the two testes and the penis. The testes produce sperm, and the penis releases the sperm out of the body. The sperm are produced in tubules within the testes and then mixed with fluid and stored until they are released.

Figure 6 The reproductive organs in males and females are different. The male testes make sperm that are released from the body through the penis. The female ovaries make eggs. An egg that is fertilized by sperm develops into a fetus in the uterus, where it is protected and nourished.

The Female Reproductive System The main organs of the female reproductive system are two ovaries, a uterus, and a vagina.

The female system has two functions, to produce eggs and to protect a developing fetus. Eggs are produced in the ovaries. If a sperm and an egg unite, the fertilized egg can develop into a fetus. The fertilized egg travels through a tube from the ovaries to the uterus. It attaches to the inner wall of the uterus and begins to develop into a fetus. The uterus provides protection and food for the developing fetus. After about nine months of development and growth, the fetus is ready to be born.

The muscles of the uterus contract, and the fetus is pushed out of the mother’s body through the vagina during birth.

Parts of the Male and Female Reproductive Systems Uterus

Testes

Testes

Penis

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Ovary

Vagina

Ovary

Comparing Animal Body Systems Comparing Skeletal Systems

Shell

Exoskeleton

Skeleton

Comparing Circulatory Systems

Heart

Heart

7. Body Systems in Other Animal Species You may not look like a grasshopper or a snail, but there are many ways that your body is similar to theirs. How do human body systems compare to those of other types of animals?

Because other types of animals have similar needs for energy and resources as humans, their body systems can have similar structures and functions to human body systems. For example, even snails, insects, and fish have circulatory systems made up of a heart and blood vessels. This fish’s circulatory system works like a human circulatory system. Other animals, like snails and grasshoppers have an open circulatory system, meaning oxygen and nutrients dissolved in fluid do not have to stay in the tubes of the blood vessels until they reach their destination. Instead, the body is soaked in this fluid. Even though this system is not exactly like the human system, it has the same function of pumping oxygen and nutrients throughout the body.

Although neither a snail nor a grasshopper has bones, it has a form of a skeletal system that gives the body structure, support, and protection. A grasshopper’s exoskeleton is a version of a skeleton on the outside of its body. A grasshopper’s muscles are attached to its exoskeleton in the same way that a human’s muscles are attached to his or her bones. Even a snail’s shell provides similar functions that a skeletal system does in the human body, especially protection.

Heart

Figure 7 All of these animals have ways to support the body like a skeletal system does in humans. Some have shells, while others have skeletons or exoskeletons. The animals all have a circulatory system that transports oxygen and/or nutrients throughout the body.

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8. Plant Body Systems A Venus flytrap is a plant that catches insects and digests them, using the digested food for growth. Does this plant have a digestive system, like in humans or other animals? Although these plants don’t have a stomach or a small intestine, they have systems that have similar functions to the body systems you have learned about. Even plant species that don’t catch animals for food are in many ways similar to humans and other animals. What systems in plants have similar functions to those in humans?

Structures Like the Human Skeletal System Plants’ stems have a function similar to that of an animal’s skeletal system. Plants don’t have skeletons or shells, but their rigid stems hold a plant upright and give it support. Stems also hold the leaves up to sunlight so that they can make food. In addition, a plant’s root system anchors the plant in soil so that it doesn’t blow over in wind.

A plant’s circulatory system carries food, water, and nutrients between its roots and leaves. The human circulatory system does essentially the same thing. If you look closely at a leaf, you can see these tubes branching off and traveling to the different parts of the leaf.

Structures Like the Human Circulatory System Many species of plants have a circulatory system in their stems that consists of two sets of long hollow tubes. Xylem tubes carry water and dissolved nutrients upward from the roots to the leaves. Phloem tubes carry food from the leaves, where it is made, to all parts of the plant. If you cut a stalk of celery crosswise, you can see tiny bundles of these tubes.

You can also see these branching tubes on the top and bottom surfaces of some leaves. Like blood vessels in humans, these tubes carry food, water, and nutrients all over the body of the plant.

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Stomata

Structures Like the Human Respiratory System Plants also have a respiratory system, which is responsible for taking in air and releasing waste. However, unlike in animals, plants take in carbon dioxide and get rid of oxygen. Plants need carbon dioxide to make food by a process called photosynthesis. They also must get rid of excess water vapor as well as oxygen, a waste material from photosynthesis. Like the lungs, plants have structures that help regulate this exchange of gases in the air. Plants have stomata, which are tiny openings in leaves that act like a plant’s respiratory system. Stomata are generally too small to be seen by eye, so you need a microscope to take a picture of the stomata on a plant leaf. Stomata open and close to control how much gas passes through. Carbon dioxide enters the plant from the atmosphere, and oxygen and water vapor exit.

This is a very close-up photo of opened and closed stomata on the underside of a plant leaf. Stomata are part of the plant’s respiratory system. They regulate how much carbon dioxide is taken in and how much oxygen and water vapor is released.

Structures Like the Human Reproductive System The function of a plant’s reproductive system is to produce offspring, just like an animal’s reproductive system. Also, like animals, plants make sperm and eggs. Often, sperm can be found within pollen and eggs can be found within flowers. In many plants, a fertilized egg will develop into a seed, in the same way that a fetus can form from a fertilized egg in humans.

Interestingly, some plants are able to make sperm and eggs within the same plant, so not all plants can be distinguished as male or female.

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9. Model Systems for Research

In 1632, Rembrandt attended a dissection for training doctors. Soon after, he painted The Anatomy Lesson of Dr. Nicolaes Tulp. Before model systems were readily used, body systems were learned primarily by dissecting dead bodies.

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How do people know so much about body systems? How is it possible to know how the heart and lungs interact when you cannot see through a person’s skin into their body? And, how can a scientist learn to treat a person that has problems with the interaction between his or her heart and lungs as the result of a disease?

Today, there are lots of different technologies that help doctors see into someone’s body, but people have known about the heart and lungs before these technologies were made. One way that people have learned about body systems is through dissections of the bodies of people who have died. Although body dissections have occurred since around 200 b.c.e., in the 1500s, scientists began to dissect bodies as a way to answer questions about the body and train medical doctors.

Studying the body after death is helpful for learning about structures but not always helpful for developing treatments to diseases that affect body systems.

Another way scientists have learned about body systems and diseases is by using model organisms. As you learned, many organisms have similar body systems to humans. Diseases in humans can take many years to develop. But scientists can learn about the disease faster by studying organisms, like mice, that develop a disease or its symptoms in only a few weeks. Similarly, fruit flies have been used to learn about heart failure, problems with body development, and even sleep needs in humans. Other model organisms, even plants, yeasts, or bacteria, are used for different kinds of studies, like understanding cancer.

Using model organisms is a controversial issue in many societies.

Decisions about which species can or cannot be used in scientific research are affected by the values and the needs of the society. In general, scientists are open to new ideas, including good alternatives to living model systems, when they can be used to answer a question.

Model organisms, like fruit flies, can and have been used to learn about diseases that affect human body systems.

LESSON SUMMARY

Interacting Body Systems The Skeletal and Muscular Systems The skeletal and muscular systems work together to provide structure for the body and allow for body movement.

The Digestive System The body gets nutrients and energy from food. The digestive system breaks down food into nutrients from which energy can be released. It also gets rid of solid waste.

The Respiratory and Circulatory Systems The respiratory and circulatory systems work together to get oxygen all over the body and to remove carbon dioxide waste.

The Excretory System The excretory system gets rid of waste. The urinary system is part of the excretory system. It removes liquid waste from the blood and regulates the amount of water in the body.

Body Systems Work Together Body systems work together. Without this cooperation, the body would not function.

The Reproductive System The organs of the male reproductive system produce sperm. The organs of the female reproductive system produce eggs. An egg fertilized by a sperm can form a fetus.

Body Systems in Other Animal Species Non-human animals have needs that are fulfilled by their body systems, like in humans.

Plant Body Systems Plants have body systems with similar functions to those of animals. They help a plant meet its needs.

Model Systems for Research Scientists often use model organisms to understand functions of the body that cannot be understood from direct observation of the human body.

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Levels of Organization How do organs, tissues, and cells work together to make up your body systems?

Introduction

Vocabulary

What is this unusual image a photograph of? This is a close-up image of a small part of the respiratory system. It shows the inside of the trachea, the tube through which air travels from the mouth and nose to the lungs. If you could look at the inside of your trachea, it might look like an ordinary tube. But if you could zoom in really closely, you would see details such as these hairy structures waving around.

Scientists and engineers have developed tools for looking closely at structures. These tools, called microscopes, allow them to see things that they would never be able to see with just their eyes. Using microscopes, they have learned that structures, such as organs, are made up of smaller parts that work together to make a functioning whole. Do you think that all body parts look like the trachea under a microscope?

In the previous lesson, you explored how body systems are made up of organs that work together. In this lesson, you will learn about microscopes and how they have been used to learn about what makes up different organs. You will learn that organs are made up of smaller subsystems called tissues, which are made up of even smaller parts, called cells. You will find out that each of these body parts has a unique structure that is very well suited for its function. All of these systems and subsystems work together to make a functioning human.

magnification the enlarged appearance of an object when viewed through a microscope cell the smallest unit of life; A cell has a distinct shape and function tissue a group of structurally similar cells that work together to perform a specific function; a level of organization above cells cross section a thin slice of an organ or tissue made by cutting through it

Next Generation Science Standards Performance Expectations MS-LS1-3. Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

Science and Engineering Practices Engaging in Argument from Evidence Use an oral and written argument supported by evidence to support or refute an explanation or a model for a phenomenon.

Crosscutting Concepts Systems and System Models Systems may interact with other systems; they may have subsystems and be a part of larger complex systems.

Science is a Human Endeavor

Disciplinary Core Ideas LS1.A. In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions.

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1. Microscopes Reveal Small Structures You have read about scientists who performed human dissections in the 16th century. These scientists never saw structures like the hairy-looking inner surface of the trachea because these structures are too small to be seen by the human eye. Over time, scientists and engineers have come up with tools that allow them to see these tiny things. One of the most impactful of these tools is the microscope.

The invention of the microscope allowed people to see that there were organisms living all over. The earliest microscopes were used to see and describe the many bacteria, yeasts, and other living things found in a drop of pond water. Many microscopes still work like the earliest ones, by shining light through lenses to magnify an object. Magnification refers to the enlarged appearance of an object when viewed through a microscope. When an object is magnified, new details can be seen.

The invention of microscopes also allowed scientists to gather the evidence needed to support the idea that all living things are made up of small structures they called cells. A cell is the smallest unit of life, meaning it is the smallest thing that can be considered alive. This was a huge discovery for the field of biology. Since then, scientists have been using microscopes to study cells and other tiny structures.

Cells are not only tiny, they are also generally colorless. For this reason, cells and other body parts are often stained before they can be seen using a microscope. Stains allow biologists to study the internal structure of body parts. Stains also make it easier to see how cells are arranged in groups called tissues. A tissue is a group of structurally similar cells that work together to perform a specific function in an organism.

To observe structures that are too small to be seen with the unaided eye, scientists often use microscopes. The bottom image shows what modern microscopes used in labs look like. Microscopes are used to see the details of cells and how groups of cells form tissues. In the top image, brain tissue samples have been stained to make their structures more visible under a microscope.

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Scientists use different kinds of microscopes for different purposes.

Each type of microscope can add new understanding to the structure of a body part. Some microscopes can view only the outside surface of a specimen. Others can view internal structure.

A scanning electron microscope (SEM) scans the surface of a specimen to produce a three-dimensional image of the surface. The SEM image of the fly eye shows how hairy the fly is and how the eye is made of a collection of smaller parts that look like tiny circles. A scientist might look at this and wonder if each of those smaller circles is attached to anything inside the eye. They might design another experiment using a different kind of microscope to see what is inside the eye.

Most objects need to be cut open in order to see inside. A cross section is a slice of an organ or tissue made by cutting through it. The process of cross sectioning damages the original structure’s surface, which prevents you from examining the surface of the structure in its original form. There is more than one type of microscope scientists use to study the inside of a structure, but one option is a light microscope (LM). The microscopes you use in your classroom are likely LMs. Cross sections studied by LM are often stained so that the image will show up as the color of the stain, like pink. This LM image of the fly eye shows structures that couldn’t be seen using the SEM, such as the organization of parts inside of the eye.

The scanning electron microscope image on the left shows the texture of a fly eye’s surface. The image on the right is a stained cross section of a fly eye as seen through a light microscope. Each tool allows you to see a different kind of view of the same thing and has different strengths and weaknesses.

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2. Levels of Organization How do you organize your computer files and folders so that files are easy to locate? Many people place subfolders inside more general folders. The human body and other complex organisms are organized in a similar way. The system is called levels of organization.

Cells The cell is the smallest thing that can be considered living. In biology, a cell is called the smallest level of organization of the body.

Some organisms, like bacteria, are made of only one cell, which performs all functions for the organism. Many organisms, however, like humans, contain trillions of specialized cells. Cells are very different in structure depending on their function. A cell that works with trillions of other cells to perform all of life’s functions will be different than a cell that performs all of its life functions itself. For example, a bone cell has long projections to connect to other bone cells, while a bacterial cell might not because it might survive without needing to touch nearby cells.

Figure 2 These pictures show the levels of organization of a human, using bone as an example. Different bone cells make up the tissue in bones. Different tissues in the bone make up the bone, an organ. One bone is an organ in the body system called the skeletal system. All body systems interact to make up a functioning organism.

Tissues Tissues are groups of similar cells that work together, so they are the second level of organization. For example, bone tissue is a collection of cells that help the bone create its rigid but lightweight structure. There are four major types of tissues: connective, epithelial, nervous, and muscle tissue. Bone tissue is a type of connective tissue.

Connective tissue protects other tissues and holds the parts of the body together. Epithelial tissue, such as skin tissue, covers body surfaces.

Nervous tissue is the tissue that makes up the brain. Muscle tissue helps with movement and makes up the muscles of the body.

There are also subtypes of tissue. For example, there are two main types of bone tissue: compact and spongy bone. Compact bone tissue gives bone its strength and hardness because the material in compact bone is dense, providing strength. Spongy bone tissue is full of spaces like a sponge. The spaces allow the bone to be lightweight.

Levels of Organization From Bone Cells to Body Bone cell

Cell

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Tissue

Organs Two or more different kinds of tissues grouped together form an organ. Organs are the next highest level of organization. Each bone is an organ. And, as you read, bone is made up of two different kinds of connective tissue that give the bone its strength and lightweight properties. Compact bone tissue forms the outer layer of a bone and makes up most of the long bones of the arms and legs. Spongy bone tissue is found inside the bone. You may have heard of bone marrow, the substance that makes blood cells. Bone marrow is a tissue that fills the spaces of spongy bone tissue in the bone’s center. Blood vessels also run through bones. All together these different tissues make a functional organ. An adult human has more than 200 bones plus many other organs. The stomach, the eyes, the brain, the kidneys, and the lungs are all organs.

Body Systems A group of organs that work together form a body system, the next level of organization. You have already learned about several body systems and how they interact with one another. All the bones together make up the skeletal system. The skeletal system has three functions. First, it provides support for the body so that you can stand upright. Second, it allows the body to move in many different ways. Third, it provides protection to internal organs, such as the lungs, heart, and brain. Other examples of body systems are the muscular, digestive, respiratory, circulatory, and reproductive systems. Each has its own function in the body.

Organisms An organism is the highest level of organization of a body. All of the body systems together make up an organism. Many other animals have the same levels of organization as humans; their cells make up their tissues, which make up their organs and body systems, which make up the organism. But, not all organisms have all of these levels of organization.

Bone tissue

Organ

Bone

Body system

Organism

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Cell Structure and Function Relationship Cell

Structure

Function

Heart muscle cell

Long narrow cells are stretchy so that they can contract and relax lengthwise like a rubber band.

Skin cell

Flat, square-shaped cells connect together tightly to form a barrier between the inside and the outside of the body.

Skeletal muscle cell

Tube-like cells join together to form a long string of cells. The long strings act like elastic to stretch and contract muscle tissue.

Small intestine lining cell

Tall, column-shaped cells look like bricks standing on end. They fit together to form a strong barrier so that digestive juices do not leak out of the intestine.

Bone cell

Long projections of the cell connect to allow cells to interact from a distance, through dense material made by the cell. This allows to bone to be strong but lightweight.

Figure 3A Different kinds of cells can be found in different parts of the body. Each cell type has a different shape depending on its function. The shape of each cell helps it to carry out its job within the tissue.

3. Cell and Tissue Structure and Function The shape of an object and its function are often related. For example, you could not eat soup with a fork because the fork cannot scoop up liquids. You could not spear a piece of meat with a spoon because the spoon has no sharp points. In the same way, the shapes of cells that make up a tissue and the tissue’s function influence each other. In addition, the shapes of tissues in an organ and the organ’s function influence each other.

The Shape and Function of a Cell Are Related You can tell a lot about the job of a cell by looking at its shape. The cells that make up the different tissues within an organ have distinct shapes that help them carry out their function. For example, epithelial cells in the skin are flat and square-shaped. Their shape is well-suited for fitting together into a solid protective covering for the body. Muscle cells are long and narrow for contracting and relaxing, much like a rubber band’s shape and function. Red blood cells are disc-shaped and flexible so that they can squeeze through narrow blood vessels. The hairylooking cells of the trachea that you saw at the beginning of the lesson use those hair-like parts to trap any particles that were inhaled. This prevents the particles from entering and damaging the lungs.

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The Structure and Function of a Tissue Are Related Tissues in different organs look different, even if those organs are part of the same body system. This is because each tissue has a different function depending on where it is located. For example, the tissues that make up the esophagus look different than the tissues that make up the small intestine, even though they are both part of the digestive system. The inner wall of the small intestine has folds called villi that help to absorb nutrients, but the inner wall of the esophagus does not. Why are these two structures different? The answer can be found in the functions of the esophagus and the small intestine.

The esophagus is a hollow tube. Its walls are made up of different kinds of tissues. Each kind of tissue contributes to the function of the Figure 3B esophagus—to move food from the mouth to the stomach. Smooth These two images, made with a light epithelial tissue lines the inside wall of the esophagus and separates microscope, show tissues in two the rest of the body from the partly digested food. Surrounding digestive organs. The tissues of the the epithelial tissue is a layer of connective tissue that supports the esophagus look different from those of epithelial layer. Layers of muscle surround the connective tissue. When the small intestine because the tissues muscles in this layer contract, they push food through the esophagus. within these organs have different A final layer of epithelial tissue covers and protects the outside of the functions in the digestive system. esophagus. Each kind of tissue in the esophagus contributes to the function of moving food.

The wall of the small intestine is Tissue Structure and Function Relationship composed of the same layers of tissue as the esophagus wall. However, as you can see in Figure 3B, the structure of these tissues is different. The small intestine has folds along the inner part of the tube. The tissue of the small intestine Smooth tissue of is different because the function of the the esophagus small intestine is different. The tissues on the inside of the small intestine don’t need to be smooth because food passes through it very slowly. In fact, the folded surface helps the small intestine take in more nutrients from the digested food.

The tissue of the small intestine also has specialized epithelial cells that produce and secrete digestive juices.

Even though both of these organs are important for the overall role of digesting food in the digestive system, they do different jobs in the digestive Folded tissue of the system. Their different structures reflect small intestine their different functions within the digestive system.

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4. Organ Structure and Function The steering wheel of a car is a very different shape than the brake pedal because these parts have different functions. In the same way, the whole small intestine looks different than the lungs, even though they are both organs in the body. How do the shapes of these organs allow them to do their jobs?

Figure 4A An organ’s surface area is related to how much absorption can occur.

The more surface area, the more absorption that can take place. The function of the small intestine is to absorb nutrients from digested food.

The small intestine has folds that add surface area and make nutrient absorption more efficient.

Absorption and Surface Area The job of both the lungs and the small intestine is absorption. The lungs absorb oxygen from the air, and the small intestines absorb nutrients from digesting food. While the structure of these two organs is very different, they both have organ surfaces that are shaped for absorption.

Figure 4A represents tissue sections of two different kinds of organs.

One of the two tissue sections is better at absorption. How do you know which is which? Compare the flat tissue on the left to the folded tissue on the right. Both take up the same amount of space, but the folded tissue has a much larger surface that nutrients can pass though, like in the small intestine. If you stretched out the folded tissue until it was flat, the surface exposed for absorption would be more than twice as large as the surface in the flat tissue on the left. So, having folded tissue allows an organ to have a large surface area for absorption while still taking up a small amount of space.

Absorption in the Lungs Your two lungs are large spongy organs that take up most of the space in your chest. They are structured to exchange gases between the blood and the outside environment.

Oxygen is brought into the body through the lungs and passed to blood vessels. Carbon dioxide is passed from the blood vessels to the lungs to be exhaled as waste from the rest of the body. How are the lungs structured to aid in the exchange of these two gases in the body?

Absorption Increases With Increased Surface Area More surface area Less surface area

Less absorption

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More absorption

Alveoli and Surface Area in the Lungs Trachea

Blood vessels

Lungs

Alveoli

Like the small intestine, the lungs are structured to have more surface area for better absorption. Except, instead of absorbing nutrients through folds in the tissue, the lungs absorb oxygen through tissue shaped into many tiny air sacs. Oxygen is required for the life processes that release energy from nutrients. It is inhaled into the lungs through tubes traveling down from the nose and mouth. The tubes divide into smaller and smaller branches. At the ends of the branches are grapelike clusters of flexible air sacs called alveoli. Air enters the alveoli when you inhale. The alveoli expand like tiny balloons. A balloon-like structure is well-suited for holding air, and clusters of millions of balloons are great for holding a lot of air.

The structure of the alveoli are important for gas exchange, the main role of the lungs. The walls of the alveoli are very thin. Oxygen easily passes through the walls and into the tiny blood vessels that are wrapped around the alveoli. At the same time, carbon dioxide waste passes from the blood vessels into the alveoli. It leaves the body when you exhale. The millions of alveoli in each lung provide a very large surface area through which oxygen can pass into the blood and carbon dioxide can be removed. If the lungs were two large, empty balloons without the tiny sacs, there would not be enough surface area for gas exchange and you would not survive. Like the lungs, every organ in the body is structured to carry out its function effectively.

Figure 4B The structure of the lung is important for its function. Lungs exchange oxygen and carbon dioxide between the outside air and the blood that carries these gases around the body.

Each lung contains millions of tiny balloon-like alveoli that provide a large surface area for exchanging gases.

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Key Science Concept

Levels of Organization in the Body The five levels of organization in complex living things are the cell, tissue, organ, body system, and organism.

The cell is the least complex living thing and the organism is the most complex. At every level in an organism, including your own body, structure is related to function.

The shape of heart cells allows them to connect with each other and create a strong, elastic tissue that expands and contracts when blood enters and is pumped out.

The shape of skin cells allows them to fit tightly next to each other. The many layers of stacked skin form a tissue that is a protective barrier between the inside and outside of the body.

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Skeletal muscle cells fuse together to make long strings of cells. Bound next to other long strings of skeletal muscle cells, they form a tissue that can contract or stretch out to help with movement.

The shape of the cells lining the small intestine allows them to form a tight barrier, keeping digestive juices in the intestine.

The tissue of the small intestine is shaped to increase surface area for absorption of nutrients.

The shape of bone cells allows them to attach to one another. Tissues with dense bone cells give the bone its strength, while tissues with more space between cells helps the bone remain lightweight.

5. Organization of Different Organisms Sponges are animals that live in the ocean. You might confuse them for colorful plants because they have no eyes, ears, nose, legs, arms, or even a head. But without these body parts, how do sponges acquire nutrients and get rid of wastes?

Not all organisms have the levels of organization that humans do.

Sponges, for example, have no organs or body systems. In fact, they don’t even have what scientist call true tissues. They have cells in layers that work together to perform a function, but they do not have the four major types of tissues. Their bodies look like large, hollow tubes attached to the ocean floor. Sponges are still able to get nutrients and oxygen for their cells by filtering food and oxygen out of the ocean water that passes through their bodies. Since different organisms have different ways of meeting their needs, scientists have to be open to new ideas about the way body systems can work. As more organisms are studied and understood, new ways of carrying out life processes are being found.

Not all organisms have the same levels of organization that humans have. Sponges are an example of an animal that has cells, but no organs, true tissues, or body systems.

LESSON SUMMARY

Levels of Organization Microscopes Reveal Small Structures Microscopes magnify objects so that details that you cannot see with the eye alone can be seen. Scientists using microscopes found that organs are made up of tissues and cells. A cell is the smallest unit of life that has a distinct shape and function. Scientists use different kinds of microscopes for different purposes.

Levels of Organization A functioning human has five levels of interacting structures. The smallest unit is the cell. Cells group together to form a tissue. Two or more tissues form an organ. Organs are grouped into body systems. Body systems allow the organism to perform all life functions.

Cell and Tissue Structure and Function Each cell type has a distinct shape because it plays a unique role. Each kind of tissue contributes to the function of an organ in different ways. Their different functions are reflected in their different structures.

Organ Structure and Function An organ’s structure is important for its function. The larger the surface area of a structure, the more material it can absorb. Organs like the lungs and small intestine have structures that help increase the surface area of absorption.

Organization of Different Organisms Not all organisms have the levels of organization that humans have. Sponges are a type of organism that have cells, but don’t have organs or body systems. They even lack true tissues. Scientists are open to new ideas and have learned different ways organisms carry out their life processes.

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Controlling Body Systems How does your nervous system sense and respond to a constantly changing environment?

Introduction Hidden behind your eyes, protected by a thick layer of bone and floating in a pocket of fluid, is the organ of your body that controls all of the other body systems, your brain. Your behaviors, all your memories, your thoughts, and your feelings are created and stored in your brain. Basically, if you had to pinpoint a part of your body that determines who you are, it would be your brain. The brain may be the most obvious part of the nervous system, but this system has other parts, too. How do your brain and the other parts of your nervous system work together to sense and respond to a constantly changing environment?

This illustration of the brain and other parts of the nervous system will help you begin exploring this system. The yellow lines represent nerves, which form a network that connects all parts of the body to the brain. Like traffic on a busy highway, signals pass along the nerve network to and from the body’s other organs and the brain.

In this lesson, you will apply what you have previously learned about levels of organization to exploring the cells, tissues, and organs of the nervous system. First, you will see how the other body systems communicate with the nervous system and how that information is processed in the brain. Then, you will learn that the outcome of that information processing can result in a behavior, memory, and/or emotion. As you delve into this topic, look for the many cause and effect relationships that, together, allow you to make predictions about how your nervous system functions.

Vocabulary nervous system the body system that collects and responds to information from inside and outside of the body; consists of the brain, spinal cord, and a network of nerves neuron the main cell of the nervous system that transfers signals to, from, and within the brain spinal cord an organ of the nervous system that transfers information between the brain and other parts of the body brain an organ of the nervous system that processes information received from both outside and inside of the body nerve a bundle of nerve cell axons that transmit information to and from the brain and spinal cord stimulus a change in the internal or external environment that causes the nervous system to react sense receptors specific kinds of neurons that detect stimuli from outside or inside of the body

Next Generation Science Standards Performance Expectations MS-LS1-8. Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.

information from multiple appropriate sources and assess the credibility, accuracy, and possible bias of each publication and methods used, and describe how they are supported or not supported by evidence.

Science and Engineering Practices Obtaining, Evaluating, and Communicating Information Gather, read, and synthesize

Crosscutting Concepts Cause and Effect Cause and effect relationships may be used to predict phenomena in natural systems.

Disciplinary Core Ideas LS1.D. Each sense receptor responds to different inputs (electromagnetic, mechanical, chemical), transmitting them as signals that travel along nerve cells to the brain. The signals are then processed in the brain, resulting in immediate behaviors or memories.

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1. Parts of the Nervous System You hear a loud noise behind you. You jump. Your heart begins to beat faster and you breathe more rapidly. When you turn around, you realize that the loud noise was caused by someone dropping a heavy book on the floor. In this example, the circulatory, respiratory, muscular, and skeletal systems in your body have worked together to respond to a change in the environment. How were all of these systems able to respond at the same time, immediately after hearing the noise?

The nervous system is the body system that collects and responds to information from inside and outside of the body. It sends instructions to the rest of the body about what to do. Signals are sent within the brain as well as between the brain and the rest of the body constantly.

Like the other body systems, the nervous system is composed of organs that are made up of tissues, which are, in turn, made of cells.

Figure 1A The structure of a neuron is important for its function in transferring signals from one cell to another. Signals from one neuron enter one side of the cell, travel through the cell body and axon, and then are relayed to the neighboring neurons through the branched endings of the axon.

Cells of the Nervous System The main cells of the nervous system that transfer signals to, from, and within the brain are called neurons. A typical neuron has three parts: a cell body, a long axon, and dendrites. The structure of a neuron is very important for its function of transferring signals. You can think of a signal passing from one neuron to the next like a relay race. The dendrites of one neuron receive signals from other neurons. The signals move through the cell body and axon, then on to the neighboring neurons through the ends of the axon. The many branched axon endings allow a neuron to pass a signal to several other neurons at once, so the signal can travel multiple places at once. For example, when you are startled by a loud noise, signals go from the brain to your muscles, to your heart, and to your lungs at the same time so that you react to the noise in several ways.

Cells of the Nervous System Cell body

Dendrites

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Figure 1B The spinal cord is an organ in the nervous system found protected inside a person’s backbone. The spinal cord is made up of multiple types of tissues including nervous and connective tissue. All these tissues work together to allow the spinal cord to function in sending signals to and from the brain and body.

Parts of the Spinal Cord and Surrounding Backbone

Nervous tissue Connective tissue

Backbone

Tissues of the Nervous System Nervous tissue is made up of different kinds of neurons, as well as other cells that support neuron function. The axons of neurons are often bundled up next to each other and covered in connective tissue forming tracks, like highways, for signals to pass between the brain and the body.

Remember that there are four kinds of tissues: nervous, connective, epithelial, and muscle. All the parts of the nervous system are made of nervous tissue and other tissues. The spinal cord is an organ that transfers information between the brain and other parts of the body.

The spinal cord is made of nervous tissue that is surrounded by a thin layer of connective tissue and blood vessels.

Organs of the Nervous System The organs of the nervous system are the brain, the spinal cord, and the nerves. The brain is an organ that processes information received from both outside and inside of the body. It is protected by the skull and is the control center for the entire body. It is also the most complex organ in the human body, consisting of almost 100 billion neurons.

The spinal cord runs down a person’s back, protected by the backbone. Most information passes through the spinal cord on the way to the brain. Signals from the responding brain also pass through the spinal cord on the way to the rest of the body.

Nerves are organs that transmit information toward and away from the brain and spinal cord. They are made up of the axons of neurons bundled together. Almost every part of the body has nerves interacting with it. To get to the various body parts at and below the neck, pairs of nerves branch off from either side of the spinal cord and into the other organs of the body. For example, nerve branches near your shoulders travel down your arms and into your hands. One side connects to your left hand and the other side to your right hand.

The organs of the nervous system are the brain, the spinal cord, and a network of nerves. The brain is the regulator of all the body systems.

Nerves transfer information to and from the brain and the rest of the body through the spinal cord.

Brain Spinal cord

Nerves

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2. Stimuli to and from the Brain

Figure 2 Nerves surrounding organs in the body send signals to the brain. For example, these nerves in the stomach transfer information about the stomach to the brain. The brain interprets the signal as a sense of hunger or fullness.

Internal Signaling to the Brain

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Your stomach “growls” and you know that you are hungry. Besides the grumbling sound, you actually might feel an ache inside your belly.

Or, when you eat too much, you can feel the fullness in your stomach.

How does that happen? How do you know what your stomach is feeling?

Nerves in your stomach are sending information to your brain and the brain is interpreting that information as hunger or fullness.

A grumbling stomach is an example of a stimulus in your internal environment. A stimulus is a change in the internal or external environment that causes the nervous system to react. An example of an external stimulus is the sound that was made when the heavy book was dropped behind you. Lights, odors, or the flavors of foods are other examples of stimuli (plural of stimulus).

Nerves are found inside and all around most of the organs in the body. If something about the organ changes, the nerve responds by sending a signal to the brain through the spinal cord. Nerves that transport signals toward the brain are called sensory nerves. Sensory nerves receive and transmit sensory information such as sounds or pressure from the other body systems and from the external environment. Motor nerves are the nerves that transmit information from the brain toward the rest of the body. Together, sensory and motor nerves relay information to and from the brain.

When the brain receives information about the change, it makes a decision and then sends information to the other body systems telling them how to respond. For example, your stomach expands when it is full. Sensory nerves around the stomach detect this change in size.

This information is sent to the spinal cord, which relays it to the brain. The brain interprets this information as the feeling of fullness and decides that it is time to stop eating. The brain then sends signals back through the spinal cord to your arm muscles, telling them to contract and put down your fork. The relaying of all this information to and from the brain usually happens in less than a second. The process of receiving a signal and interpreting it for a response is called information processing.

A response to a stimulus can also be the formation of a thought or a memory. For example, you might be excited that school is ending when you hear the bell ring. Or you Stomach might form a memory of what the bell sounds like so that you recognize it the next day.

3. Voluntary and Involuntary Responses If you have been to a check-up at the doctor’s office, the doctor might have used a small rubber hammer to hit below your knee. Then, to your surprise, your lower leg probably kicked forward. What caused your leg to act like it had “a mind of its own”?

Some responses to a stimulus are voluntary, and others are involuntary. Responses that you have to think about to control are voluntary responses. For example, moving your body to stand up from your chair after you hear the bell ring at the end of the school day is a voluntary response to the bell. Responses that you do not have to think about, such as your breathing, heartbeat, and digestion, are involuntary.

A reflex is an involuntary response. Some reflexes, like blinking in response to something coming toward your face, are controlled by the brain. But some reflexes are processed in the spinal cord and do not even require the brain for a response. The knee-jerk in response to the rubber hammer is a spinal cord reflex. Spinal cord reflexes occur quickly because the information is processed in the spinal cord and a reaction occurs before the brain even receives the information about a stimulus.

In a knee-jerk reflex, information passes from the knee to the spinal cord and then to the leg muscles. Your leg moves even before your brain recognizes the hit of the hammer. These reflexes have a very predictable cause-and-effect pattern, so any change to that pattern indicates that something is wrong. This is why the hammer test is one good test for checking how well the nervous system is responding to signals.

Figure 3 The knee-jerk reflex is a type of involuntary response called a spinal cord reflex. The stimulus is a tap just below the knee. Information travels to the spinal cord, which relays a signal to the leg muscles to jerk the leg upward. The initial stimulus does not need to be relayed to the brain for the response to occur.

Knee-Jerk Reflex Motor nerve causes muscles to contract and the leg jerks forward

Stimulus

Sensory nerve receives stimuli from hammer

Reflex response

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4. Sense Receptors You are surrounded by stimuli in both your internal and external environments—hunger, thirst, sounds, images, odors, and objects to touch and feel. Many of these stimuli are harmless, but some may be dangerous. How does your body handle all these stimuli to ensure that you survive?

Sense receptors are specific kinds of sensory neurons that detect and are activated by stimuli from outside or inside of the body. Being activated means that they initiate the signal that is sent to the brain in response to the stimulus. They are found in and around almost every organ in the body.

Some sense receptors monitor internal conditions. For example, Figure 4A heat and cold receptors throughout the body detect changes in The body has several types of sense temperature. Other sense receptors in blood vessels detect changes in receptors, such as mechanical blood pressure. Receptors all over the body even detect changes in the receptors. The skin has many body’s position or pressure and pain in different regions of the body. mechanical receptors that respond Other sense receptors detect changes in the external environment to pressure. The receptor sends this such as light, sound, and temperature. Humans gather information information to the brain, where it is from the many stimuli in the external environment through their senses interpreted as touch. of sight, hearing, smell, taste, and touch. Although these stimuli are different, the body responds to them in a similar way. First, a stimulus is detected by Signaling from Mechanical Receptors a sense receptor. Second, a signal is sent to the brain. Third, the brain responds. It can respond by sending a signal to trigger a behavior, thought, emotion, and/or the creation of a new memory.

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Mechanical Receptors There are many kinds of sense receptors, and each kind responds to a different kind of stimulus. A mechanical receptor is a sense receptor that detects and is activated by movement.

Mechanical receptors are found all over the body. Mechanical receptors in the stomach detect how much food is inside by how stretched the tissue in the stomach is. Mechanical receptors in the inner ear allow you to hear, using the movement of tiny hairs in the inner ear in response to sounds. Mechanical receptors in the skin are able to interpret different kinds of pressure as different kinds of touch, like soft touch or vibration.

Chemical Receptors Sense receptors that detect and are activated by chemical substances are called chemical receptors. Chemical receptors are found in the mouth and nose. Taste buds are structures on the tongue that contain chemical receptors. The receptors are activated by chemical substances you put in your mouth, such as sugars in foods and beverages. Chemical receptors send signals to the brain that are interpreted as taste or smell. Chemical receptors are important for survival. The ability to smell and taste allows animals to distinguish fresh food from a toxic substance. Smell and taste keep many animals, including you, from poisoning themselves.

Light Receptors Light receptors are sense receptors that detect and are activated by light. Light receptors are part of a category of receptors called electromagnetic receptors. Light receptors in the eye absorb light and trigger nerve signals that result in sight. Light hitting your eye is a stimulus. You see when light reflects off an object, enters the eye, and activates the light receptors at the back of the eye. The information is sent to the brain through sensory nerves and processed to form an image. Without these receptors, you would not be able to see.

The human eye contains two kinds of light receptors with different functions—rods and cones. Rods respond to dim light and to motion, but they cannot detect color. Cones help to interpret light of different colors. Humans have three kinds of cones. One responds to red light, one responds to blue, and the third responds to green. All of the colors you see result from the interaction of signals sent to the brain from these three kinds of cones.

Figure 4B Mechanical receptors in the skin, chemical receptors in the tongue, and light receptors in the eye all detect and are activated by specific stimuli in the environment. All sense receptors are the starting points of signals to the brain that are interpreted as sight, sound, smell, taste, or touch.

Sense Receptors and Their Locations

Light receptors in the eye

Chemical receptors in the nose

Chemical receptors on the tongue

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5. Memory, Learning, Thoughts, and Emotions You walk into a room and smell a familiar scent. It reminds you of your best friend and one day that you couldn’t stop laughing together.

This memory makes you happy. How does the nervous system do this?

You have learned that behaviors, like moving your leg, are the result of information processing. Thoughts, feelings, learning, and memory can also be the result of information processing. In the example you just read, the stimulus was the smell and the response was a series of thoughts, memories, and feelings that all happened within your brain.

The Hippocampus and Memory

Hippocampus

Memory Some types of information processing result in the formation of new memories or recalling old memories. For example, you have formed a memory of your favorite food because your brain processed the information from the chemical receptors in your tongue when you ate and enjoyed that food. Now you can remember what it tastes like without even having to eat it.

There are two kinds of memory: short-term and long-term. Shortterm memory, often called working memory, acts as temporary storage for information that is being processed at a given point in time. In order to solve a math word problem, for example, you need to keep in mind the beginning of the problem while you read the rest of the problem, but you don’t need to remember it five days later. Long-term memory is used to store information in the brain over long periods of time, sometimes your entire life. The building of a long-term memory involves permanent changes to the connections between different neurons in the brain. Short-term memory often becomes long-term memory as these changes occur.

Forming new memories generally requires a part of the brain called the hippocampus. The hippocampus is located deep inside the brain. Once these memories are made, they are stored as long-term memories all over the brain.

Figure 5 One of the main regions of the brain for creating new memories is the hippocampus.

Memory can be one of the results of information processing in the brain.

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Learning Learning is also a result of information processing.

Learning and memory are closely related. Learning is the process for making new memories, and remembering what you have previously learned is important for learning new things. For example, when you learned how to read, your brain had to store the relationship between letters and words and what they meant. If it weren’t for memory, you would have to relearn these things every time you pick up a book. Also, like memory, learning causes structural changes in the brain, changing the connections between different neurons.

Some behaviors change as we age, but learning is a behavior that lasts a lifetime. What we learn can and does change as we get older.

For example, you probably learned to talk and walk as a toddler. Young people will often learn brand new ideas faster than older people. But older people can often connect different ideas together better because they have more memories of similar information to connect with the new information.

Learning, such as learning to use a tablet, can happen at any age. Each member of this family uses the senses of sight, hearing, and touch while learning. Information from the senses is sent to their brains, where it can be used immediately or processed and stored as memories.

Thoughts and Emotions Thoughts and emotions can also occur as a result of information processing. How you think about and feel toward a stimulus can change how you interact with that stimulus. For example, if it makes you happy when you ride a bike or skateboard, you might try to do it more often. But if you have negative feelings toward these things, you will likely avoid them.

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Key Science Concept

Stimuli and Responses While Cooking Stimuli and Responses have a cause and effect relationship. A stimulus might cause a sensory receptor to respond by sending signals to the brain. The brain responds to the signals, and the effect will be a behavior, memory, thought, or emotion. Some stimuli, like heat, activate pain receptors in the skin. Responses to these stimuli result in reflex responses that do not need to be sent to the brain for immediate action.

Stimulus From Pain Receptors Receptors in the hand send signals to the spinal cord.

Stimulus From Light Receptors Light receptors in the eye send signals to the brain.

Stimulus From Chemical Receptors Chemical receptors on the tongue send signals to the brain.

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Reflex Response The spinal cord sends signals immediately back to the arm, causing it to jerk away from the heat.

You respond before your brain knows what happened.

Motion Response The brain interprets the signals as sight. The soup looks ready to eat.

Signals are sent from the brain to the arm to pick up the spoon and taste the soup.

Thought Response The brain interprets the signals as taste.

Yum…but it needs more pepper.

It responds with an emotion and thought about how the soup tastes.

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Regions of Information Processing in the Brain Motor control

Speech

Touch and pressure

Taste

Body awareness

Language

Smell

Vision

Hearing

Figure 6 Scientific reports describe how working with brain patients led to evidence that different regions of the brain are responsible for processing different types of information. Different kinds of stimuli are processed in different brain regions.

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Reading

6. Regions of the Brain In the 1950s a man known as H.M. underwent surgery to remove a part of his brain that was causing seizures, a condition in which a person can lose consciousness or suddenly shake all over his or her body. He had a normal memory before the surgery, but afterwards, he could not form new memories. He was still able to walk, talk, and perform short tasks. He could even recall things from childhood, but he could not learn any new information. From H.M.’s surgery, scientists realized that the parts of H.M.’s brain that were removed, including part of the hippocampus, were needed for forming new memories. Why did his surgery only affect his memory but not other things that the brain controls? How is it possible to remove portions of a person’s brain and the person remains alive after the surgery?

Evidence from studying H.M. and the brains of other patients has supported the claim that different regions of the brain are important for processing different kinds of signals. For example, vision is processed by a region near the back of your brain known as the visual cortex. This is because the eye’s sense receptors connect to the visual cortex. Odors, tastes, and sounds are all processed in different regions of the brain. As scientists learned from H.M., even something as complicated as making new memories happens mostly in one part of the brain. However, some signals are processed in more than one region, like the process of painting. The visual cortex of the brain is used to analyze the shapes and colors on the canvas and the motor region of the brain is used to move your hand.

Scientists have learned that an injury to a particular region of the brain results in a loss of a specific function rather than a loss of all functions. For example, if someone has had an injury to the vision section of their brain, it will not injure their hearing. This predictable cause and effect pattern also works for understanding diseases.

Alzheimer’s disease affects the creation of new memories. Predictably, neurons in the hippocampus are some of the first cells to be affected by this disease. Similarly, Lou Gehrig’s disease, also known as amyotrophic lateral sclerosis (ALS), injures motor neurons, especially in the motor control region of the brain.

Scientists now have techniques for studying brain regions in noninjured brains. Imaging technologies are used to see which regions of the brain are being used when certain types of information are being processed. Functional magnetic resonance imaging (fMRI) devices are used to see, in real time, which regions are sending or receiving signals in response to a stimulus.

LESSON SUMMARY

Controlling Body Systems Parts of the Nervous System The nervous system includes the brain, spinal cord, and nerves.

The parts of the nervous system are made of nervous tissue, which is made of neurons and other kinds of cells.

Stimuli to and from the Brain The brain processes signals from stimuli in both the internal and external environments and responds to it. Sensory nerves receive signals from the environment and transmit them to the brain. Motor nerves send signals from the brain to the other organs.

Voluntary and Involuntary Responses There are two kinds of responses to a stimulus, voluntary and involuntary. A reflex is an involuntary, rapid, automatic response to a stimulus. Spinal cord reflexes are processed in the spinal cord.

Sense Receptors Sense receptors detect stimuli from the environment. When a stimulus is detected, the sense receptor sends a signal to the brain. The brain either sends a returning signal resulting in an immediate behavior or a memory forming.

Memory, Learning, Thoughts, and Emotions Memory, learning, thoughts, and emotions also result from information processing by the brain. Short-term memory acts as temporary storage of information that is being processed. Long-term memory stores information in the brain over long periods of time.

Regions of the Brain Signals travel from various parts of the body to specific regions of the brain.

Scientists have gathered evidence for this understanding through various methods.

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INTEGRATED PHENOMENON When a person takes a dog on a long walk in the summer, you might see that the person is sweating but the dog is panting.

Segment Wrap Up Look back to the Segment Questions from the beginning of the segment. What concepts in each lesson did you learn that could help explain part of the Integrated Phenomenon? Make sure that you include these key ideas.

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Air Pressure and Wind Wind is the air flowing from a high-pressure area to a low-pressure area. Wind chill describes how the temperature feels colder when wind moves over uncovered skin.

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Water and the Weather Water cycles through the Earth’s system using energy from the sun and the force of gravity.

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Air Masses and Changing Weather Changes in weather result from large air masses moving around and interacting. Scientists use weather stations, radar systems, weather balloons, and satellites to gather weather data.

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Severe Weather Blizzards, tornadoes, and heat waves are types of severe weather. Heat waves occur when high-pressure systems stall over a region. Cities are at risk for heat waves because buildings and concrete trap heat.

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Traits for Survival Each species has its own set of traits. Different traits can help an organism survive threats to its survival.

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Traits for Reproduction Physical and behavioral reproductive traits increase the chances that an organism will mate. Traits for survival also increase the chance that an organism will reproduce simply by it living longer.

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Interacting Body Systems Body systems include skeletal, muscular, and digestive, among others. Scientists model these to understand functions of the body that cannot be understood from direct observation.

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Levels of Organization Organisms are systems that are made up of smaller and smaller parts. The smallest living thing is a cell, which makes up tissues, which makes up organs, which makes up body systems. For each of these parts, its structure is important for its function.

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Controlling Body Systems Body systems can respond to a constantly changing environment because they are coordinated by the nervous system. The brain processes signals from stimuli in both internal and external environments and responds to it. There are two kinds of responses to a stimulus, voluntary and involuntary.

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Segments 1

Revising Your Model Create a final model to explain this segment’s Integrated Phenomenon. As you develop your model, make sure it has these parts. What components could help explain why a person might sweat, but a dog might pant while taking a long walk on a warm day? How does your model describe the relationship between the components?

Model

Components Components are the parts that make up the model and that represent something in the real world.

You have to decide which parts of the real word to represent in your model.

Real World

Relationships The relationships in a model describe how the components interact. They help you to understand how the components of the model work together and to make predictions about the model.

Connections The connections between a model and the natural phenomenon it represents make the model useful. Models simplify the phenomenon to make it easier to observe, understand, predict, or quantify.

Explaining the Integrated Phenomenon Use your model to create a written explanation of the Integrated Phenomenon. Your explanation should include arguments made up of claims, evidence, and reasoning. What arguments can you use to explain how a human and a dog respond to a long walk on a warm day?

Phenomenon When scientists construct explanations, the phenomenon is the event or observation that they are explaining.

Phenomenon

Argument for Explanation

Argument for Explanation

Explanation

Arguments for the Explanation Scientists use arguments to support their explanation. An argument is made up of a claim, evidence for the claim, and reasons why the evidence supports the claim.

Explanation An explanation is a statement composed of one or more arguments that describe how or why the phenomenon happens.

E a r t h S y s t e m s , We a t h e r , a n d O r g a n i s m s

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