Unit 3 Science (Glencoe Red 2002)

U N I T

212

How AreBeverages &

WildlifeConnected?

33How Are

Beverages &Wildlife

Connected?

Life and the Environment

In ancient times, people transported beverages in clay jars and animal skins. Around 100 BC,hand-blown glass bottles began to be used to hold liquids. In 1903, the invention of the

automatic glass bottle-blowing machine made it possible to mass-produce bottles. They wereused for everything from milk to soda. Consumers returned the empty bottles to berefilled. In 1929, companies began experimenting with cans for bever-ages. Cans were stackable, non-breakable, and fast cooling—andconsumers didn’t have to return them. The plastic six-pack yokecame along with the popular use of cans for beverages. Thisdevice bound cans together for easy carrying. Unfortu-nately, the yokes bound more than cans. Millions of yokesfound their way into the environment where theyentangled thousands of birds, fish, and marine animals.Today, animals are still being harmed—in some casesthey are killed—by plastic six-pack yokes.

SCIENCE CONNECTIONSCIENCE CONNECTION

REDUCE, REUSE, RECYCLE Look at the packaging on the things you eat, your craftsor hobbies, or the products used in your home. Work with a partner to design amore eco-friendly package for one of these products. Make a drawing of your newpackaging and write a paragraph telling why your package is environmentallyfriendly. Share your drawings and paragraphs with your school or communitythrough a bulletin board.

Interactions of Living Things

214

88

How do Alaskan brown bearsand salmon interact? Therelationship between these

two species is clear to see. However,the Alaskan brown bear also dependson every species of insect and fishthat the salmon eats, and many non-living parts of the environment, too.In this chapter, you will learn how allliving things depend on the living andnonliving factors in the environmentfor survival.

What do you think?Science Journal Look at the picturebelow with a classmate. Discuss whatyou think this might be. Here’s a hint:This species and salmon interact. Writeyour answer or best guess in your Science Journal.

215

Imagine that you are in a crowded elevator. Every-one jostles and bumps each other. The temperature

increases and ordinary noises seem louder. What arelief you feel when the doors open and you step out.Like people in an elevator, plants and animals in an

area interact. How does the amount of space available to each organismaffect its interaction with other organisms?

Measure space 1. Use a meterstick to measure the

length and width of the classroom.

2. Multiply the length by the width to find the area of the room insquare meters.

3. Count the number of individuals in your class. Divide the area of the classroom by the number ofindividuals. In your Science Journal, record how much spaceeach person has.

ObserveWrite a prediction in your Science Journal about what might happen if the number of students in your classroom doubled.

EXPLOREACTIVITY

MXXX-??PDescription

Making a Cause and Effect Study Fold Make this Foldable tohelp you understand the cause and effect relationship of bioticand abiotic things.

1. Place a sheet of paper in front of you so the long side is at the top.Fold the paper in half from the left side to the right side. Fold topto bottom and crease. Then unfold.

2. Through the top thickness of paper, cut along the middle fold lineto form two tabs as shown. Label the tabs Biotic, which meansliving, and Abiotic, which means nonliving, as shown.

3. Before you read the chapter, list examples of biotic and abioticthings around you on the tabs. As you read, write about eachunder the tabs.

FOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Biotic

Abiotic

The EnvironmentS E C T I O N

Ecology All organisms, from the smallest bacteria to a blue whale,

interact with their environment. Ecology is the study of theinteractions among organisms and their environment. Ecolo-gists, such as the one in Figure 1, are scientists who study theserelationships. Ecologists divide the environmental factors thatinfluence organisms into two groups. Abiotic (ay bi AH tihk)factors are the nonliving parts of the environment. Living oronce-living organisms in the environment are called biotic (bi AH tihk) factors.

Why is a rotting log considered a biotic factor inthe environment?

Abiotic Factors In a forest environment, birds, insects, and other living

things depend on one another for food and shelter. They alsodepend on the abiotic factors that surround them, such as water,sunlight, temperature, air, and soil. All of these factors and oth-ers are important in determining which organisms are able tolive in a particular environment.

■ Identify biotic and abiotic factorsin an ecosystem.

■ Describe the different levels ofbiological organization.

■ Explain how ecology and the envi-ronment are related.

Vocabulary ecology communityabiotic factor ecosystembiotic factor biospherepopulation

Abiotic and biotic factors interact tomake up your ecosystem. The qualityof your ecosystem can affect yourhealth. Your actions can affect thehealth of the ecosystem.

Figure 1Ecologists study biotic and abiotic factors inan environment and the relationships amongthem. Many times, ecologists must travel tospecific environments to examine the organ-isms that live there.

216 CHAPTER 8 Interactions of Living Things

Water All living organisms need water to survive. The bodiesof most organisms are 50 percent to 95 percent water. Water is animportant part of the cytoplasm in cells and the fluid that sur-rounds cells. Respiration, photosynthesis, digestion, and otherimportant life processes can only occur in the presence of water.

More than 95 percent of Earth’s surface water is found in theoceans. The saltwater environment in the oceans is home to avast number of species. Freshwater environments, like the one inFigure 2, also support thousands of types of organisms.

Light and Temperature The abiotic factors of light andtemperature also affect the environment. The availability of sun-light is a major factor in determining where green plants andother photosynthetic organisms live, as shown in Figure 3. Bythe process of photosynthesis, energy from the Sun is changedinto chemical energy that is used for life processes. Most greenalgae live near the water’s surface where sun-light can penetrate. On the other hand, littlesunlight reaches the forest floor, so very fewplants grow close to the forest floor.

The temperature of a region also deter-mines which plants and animals can livethere. Some areas of the world have a fairlyconsistent temperature year round, but otherareas have seasons during which tempera-tures vary. Water environments throughoutthe world also have widely varied tempera-tures. Plant and animal species are found inthe freezing cold Arctic, in the extremely hotwater near ocean vents, and at almost everytemperature in between.

SECTION 1 The Environment 217

0

20

40

60

80

100

Wor

ld‘s

Wat

er S

uppl

y (%

)

Salt water

97%

3%

Freshwater

Figure 2 Salt water accounts for 97 per-cent of the water on Earth. It isfound in the seas and oceans.Only three percent of Earth’swater is freshwater.

Figure 3Flowers that grow on the forestfloor, such as these bluebells,grow during the spring whenthey receive the most sunlight.

This stream is a freshwaterenvironment. It is home to many species of plants and animals.

The seas and oceans are hometo thousands of different species.

Air Although you can’t see the air that surrounds you, it has animpact on the lives of most species. Air is composed of a mix-ture of gases including nitrogen, oxygen, and carbon dioxide.Most plants and animals depend on the gases in air for respira-tion. The atmosphere is the layer of gases and airborne particlesthat surrounds Earth. Polluted air, like the air in Figure 4, cancause the species in an area to change, move, or die off.

Clouds and weather occur in the bottom 8 km to 16 km ofthe atmosphere. All species are affected by the weather in the areawhere they live. The ozone layer is 20 km to 50 km above Earth’ssurface and protects organisms from harmful radiation from theSun. Air pressure, which is the weight of air pressing down onEarth, changes depending on altitude. Higher altitudes have lessair pressure. Few organisms live at extreme air pressures.

How does air pollution affect the species in anarea?

Soil From one enviroment to another, soil, asshown in Figure 5, can vary greatly. Soil type isdetermined by the amounts of sand, silt, and clay itcontains. Various kinds of soil contain differentamounts of nutrients, minerals, and moisture. Dif-ferent plants need different kinds of soil. Becausethe types of plants in an area help determine whichother organisms can survive in that area, soil affectsevery organism in an environment.

Biotic Factors Abiotic factors do not provide everything an

organism needs for survival. Organisms depend onother organisms for food, shelter, protection, andreproduction. How organisms interact with oneanother and with abiotic factors can be describedin an organized way.

Figure 4Air pollution can come frommany different sources. Air quality in an area affects thehealth and survival of the speciesthat live there.

When soil that receives littlerain is damaged, a desertcan form. This process iscalled desertification. Usereference materials to findwhere desertification isoccurring in the UnitedStates. Record your findingsin your Science Journal.

Figure 5Soil provides a home for manyspecies of animals.


Levels of Organization The living world is highly organ-ized. Atoms are arranged into molecules, which in turn areorganized into cells. Cells form tissues, tissues form organs, andorgans form organ systems. Together, organ systems formorganisms. Biotic and abiotic factors also can be arranged intolevels of biological organization, as shown in Figure 6.


Organism An organism is one individual from a population.

Figure 6 The living world is organized in levels.

Population All of the indi-viduals of one species that livein the same area at the sametime make up a population.

Community The populationsof different species that interact insome way are called a community.

Ecosystem All of the communities inan area and the abiotic factors that affectthem make up an ecosystem.

Biome A biome is a largeregion with plants and animals welladapted to the soil and climate ofthe region.

Biosphere The level of biological organization that is made up of allthe ecosystems on Earth is the biosphere.

Populations All the members of one species that live togethermake up a population. For example, all of the catfish living in alake at the same time make up a population. Part of a popula-tion of penguins is shown in Figure 7. Members of a populationcompete for food, water, mates, and space. The resources of theenvironment and the ways the organisms use these resourcesdetermine how large a population can become.

Communities Most populations of organisms do not livealone. They live and interact with populations of other types oforganisms. Groups of populations that interact with each otherin a given area form a community. For example, a population ofpenguins and all of the species that they interact with form acommunity. Populations of organisms in a community dependon each other for food, shelter, and other needs.

Ecosystem In addition to interactions among populations,ecologists also study interactions among populations and theirphysical surroundings. An ecosystem like the one in Figure 8A ismade up of a biotic community and the abiotic factors thataffect it. Examples of ecosystems include coral reefs, forests, andponds. You will learn more about the interactions that occur inecosystems later in this chapter.

Biomes Scientists divide Earth into different regions calledbiomes. A biome (BI ohm) is a large region with plant and ani-mal groups that are well adapted to the soil and climate of theregion. Many different ecosystems are found in a biome. Exam-ples of biomes include mountains, as shown in Figure 8B, tropi-cal rain forests, and tundra.


Figure 7Members of a penguin popula-tion compete for resources.

Figure 8 Biomes contain manydifferent ecosystems.

This mountaintopecosystem is part of the

mountain biome.

Research Visit the Glencoe Science Web site atscience.glencoe.comfor more information aboutEarth’s biomes. Make a posterto communicate to your classwhat you learn.

http://science.glencoe.com


80°

60°

30°

0°

30°

60°

Tropic of Cancer

Equator Equator

Tropic of Capricorn

Antarctic Circle

Arctic Circle Arctic Circle

IceTundraTaigaGrasslandTemperateForestsTropical RainforestChaparralSavannaDesertMountain

NORTHAMERICA

SOUTHAMERICA

AFRICA

EUROPEASIA

AUSTRALIA

IndianOcean

Antarctic Ocean

AtlanticOcean

Arctic Ocean

PacificOcean

AtlanticOcean

PacificOcean

Figure 9This map shows some of themajor biomes of the world. Whatbiome do you live in?

Section Assessment

1. What is the difference between an abioticfactor and a biotic factor? Give five exam-ples of each that are in your ecosystem.

2. Contrast a population and a community.

3. What is an ecosystem?

4. How are the terms ecology and environmentrelated?

5. Think Critically Explain how biotic factorschange in an ecosystem that has flooded.

6. Recording Observations Each person lives ina population as part of a community. Describeyour population and community. For morehelp, refer to the Science Skill Handbook.

7. Using a Database Use a database to researchbiomes. Find the name of the biome that bestdescribes where you live. For more help, referto the Technology Skill Handbook.

The Biosphere Where do all of Earth’s organisms live? Livingthings can be found 11,000 m below the surface of the oceanand on mountains as high as 9,000 m. The part of Earth thatsupports life is the biosphere (BI uh sfihr). The biosphereincludes the top part of Earth’s crust, all the waters that coverEarth’s surface, the surrounding atmosphere and all biomes, asshown in Figure 9. The biosphere seems huge, but it is only asmall part of Earth. If you used an apple as a model of Earth, thethickness of Earth’s biosphere could be compared to the thick-ness of the apple’s skin.

Compare your results with the results of otherstudents. Research how fertilizer runoff from farms and lawns has affected aquaticecosystems in your area. For more help,refer to the Science Skill Handbook.

Delicately Balanced Ecosystems


5. Cover each jar with plastic wrap and secure itwith a rubber band. Use your pencil to punchthree small holes through the plastic wrap.

6. Place all jars in a well-lit area.

7. Make daily observations of the jars for threeweeks. Record your observations in your Science Journal.

8. At the end of the three-week period, removethe Elodea stalks. Measure and record thelength of each in your Science Journal.

Conclude and Apply1. List the control and variables you used in this

experiment.

2. Compare the growth of Elodea in each jar.

3. Predict what might happen to jar A if youadded 5 g of fertilizer to it each week.

Each year you might visit the same park, butnotice little change. However, ecosystems

are delicately balanced, and small changes canupset this balance. In this activity, you willobserve how small amounts of fertilizer can disrupt an ecosystem.

What You’ll InvestigateHow do manufactured fertilizers affect pond systems?

Materialslarge glass jars of rubber bands (4)

equal size (4) pond waterclear plastic wrap triple beam balancestalks of Elodea (8) weighing paper*another aquatic plant spoongarden fertilzer metric ruler*houseplant fertilizer *Alternate materials

Goals■ Observe the effects of manufactured

fertilizer on water plants.■ Predict the effects of fertilizers on pond

and stream ecosystems.

Safety Precautions

Procedure1. Working in a group, label four jars A, B, C,

and D.

2. Measure eight Elodea stalks to be certainthat they are all about equal in length.

3. Fill the jars with pond water and place twostalks of Elodea in each jar.

4. Add 5 g of fertilizer to jar B, 10 g to jar C,and 30 g to jar D. Put no fertilizer in jar A.

SECTION 2 Interactions Among Living Organisms 223

Characteristics of PopulationsYou, the person sitting next to you, everyone in your class,

and every other organism on Earth is a member of a specificpopulation. Populations can be described by their characteristicssuch as spacing and density.

Population Size The number of individuals in the popula-tion is the population’s size, as shown in Figure 10. Populationsize can be difficult to measure. If a population is small andmade up of organisms that do not move, the size can be deter-mined by counting the individuals. Usually individuals are toowidespread or move around too much to be counted. The pop-ulation size then is estimated. The number of organisms of onespecies in a small section is counted and this value is used toestimate the population of the larger area.

Suppose you spent several months observing a population offield mice that live in a pasture. You probably would observechanges in the size of the population. Older mice die. Mice areborn. Some are eaten by predators, and some mice wander awayto new nests. The size of a population is always changing. Therate of change in population sizevaries from population to popula-tion. In contrast to a mouse popula-tion, the number of pine trees in amature forest changes slowly, but aforest fire could reduce the pine treepopulation quickly.

■ Identify the characteristics thatdescribe populations.

■ Examine the different types ofrelationships that occur amongpopulations in a community.

■ Determine the habitat and nicheof a species in a community.

Vocabularypopulation density nichelimiting factor habitatsymbiosis

You must interact with other organisms to survive.

Interactions Among Living Organisms

S E C T I O N

World population: 1950–2050 (projected)

012

3

4

5

678

9

10

Year

Source: U.S. Census Bureau, International Data Base 5-10-00.

Hum

an p

opul

atio

n (b

illio

ns)

1960 1980 2000 2020 2040

Figure 10The size of the human population isincreasing each year. By the year 2050,the human population is projected to bemore than 9 billion.

Population Density At the beginning of this chapter, whenyou figured out how much space is available to each student inyour classroom, you were measuring another population char-acteristic. The number of individuals in a population thatoccupy a definite area is called population density. For example,if 100 mice live in an area of one square kilometer, the popula-tion density is 100 mice per square kilometer. When more indi-viduals live in a given amount of space, as seen in Figure 11, thepopulation is more dense.

Population Spacing Another characteristic of populationsis spacing, or how the organisms are arranged in a given area.They can be evenly spaced, randomly spaced, or clumpedtogether. If organisms have a fairly consistent distance between

them, as shown in Figure12, they are evenly spaced.In random spacing, eachorganism’s location is inde-pendent of the locations ofother organisms in thepopulation. Random spac-ing of plants usually resultswhen wind or birds dis-perse seeds. Clumped spac-ing occurs when resourcessuch as food or living spaceare clumped. Clumpingresults when animalsgather in herds, flocks, orother groupings.


PacificOcean

AtlanticOcean

C A N A D A

U N I T E D S T A T E S

Average Count per km2

< 11–34–1011–3031–100> 100

Figure 11Population density can be shownon a map. This map uses differ-ent colors to show varying densi-ties of a population of northernbobwhite birds.

Research Visit the Glencoe Science Web site atscience.glencoe.comfor recent news about the sizeof the human population.Communicate to your classwhat you learn.

Figure 12 In some populations, such as creosote bushes in the desert,individuals usually are spaceduniformly throughout the area.



Limiting Factors Populations cannot continue togrow larger forever. All ecosystems have a limitedamount of food, water, living space, mates, nestingsites, and other resources. A limiting factor, as shownin Figure 13, is any biotic or abiotic factor that limitsthe number of individuals in a population. A limitingfactor also can affect other populations in the com-munity indirectly. For example, a drought mightreduce the number of seed-producing plants in a for-est clearing. Fewer plants means that food canbecome a limiting factor for deer that eat the plantsand for a songbird population that feeds on the seedsof these plants. Food also could become a limitingfactor for hawks that feed on the songbirds.

What is an example of a limiting factor?

Competition is the struggle among organisms to obtain theresources they need to survive and reproduce, as shown in Figure 14. As population density increases, so does competitionamong individuals for the resources in their environment.

Carrying Capacity Suppose a population increases in sizeyear after year. At some point, food, nesting space, or otherresources become so scarce that some individuals are not able tosurvive or reproduce. When this happens, the environment hasreached its carrying capacity. Carrying capacity is the largestnumber of individuals of a species that an environment cansupport and maintain for a long period of time. If a populationgets bigger than the carrying capacity of the environment, someindividuals are left without adequate resources. They will die orbe forced to move elsewhere.

Figure 13 These antelope and zebra popu-lations live in the grasslands ofAfrica. What limiting factors mightaffect the plant and animal popu-lations shown here?

Figure 14During dry summers, the popula-tions of animals at existingwatering holes increase becausesome watering holes have driedup. This creates competition forwater, a valuable resource.

What insect populations live inyour area? To find out moreabout insects, see the InsectField Guide at the back of thebook.


Figure 15The partnership between thedesert yucca plant and the yuccamoth is an example of mutualism.

Observing SymbiosisProcedure1. Carefully wash and examine

the roots of a legume plantand a nonlegume plant.

2. Use a magnifying glass toexamine the roots of thelegume plant.

Analysis1. What differences do you

observe in the roots of thetwo plants?

2. Bacteria and legume plantshelp one another thrive.What type of symbiotic rela-tionship is this?

Biotic Potential What would happen if a population’s envi-ronment had no limiting factors? The size of the populationwould continue to increase. The maximum rate at which a pop-ulation increases when plenty of food and water are available,the weather is ideal, and no diseases or enemies exist, is its bioticpotential. Most populations never reach their biotic potential, orthey do so for only a short period of time. Eventually, the carry-ing capacity of the environment is reached and the populationstops increasing.

Symbiosis and Other InteractionsIn ecosystems, many species of organisms have close rela-

tionships that are needed for their survival. Symbiosis (sihmbee OH sus) is any close interaction between two or more differ-ent species. Symbiotic relationships can be identified by the typeof interaction between organisms. A symbiotic relationship thatbenefits both species is called mutualism. Figure 15 shows oneexample of mutualism.

Commensalism is a form of symbiosis that benefits oneorganism without affecting the other organism. For example, aspecies of flatworms benefits by living in the gills of horseshoecrabs, eating scraps of the horseshoe crab’s meals. The horseshoecrab is unaffected by the flatworms.

Parasitism is a symbiotic relationship between two species inwhich one species benefits and the other species is harmed.Some species of mistletoe are parasites because their roots growinto a tree’s tissue and take nutrients from the tree.

What are some examples of symbiosis?

The yucca depends on the moth to pollinate its flowers.

The moth depends on the yucca for protected place to lay its eggs and a source of food for its larvae.

Section Assessment

1. Name three characteristics of populations.

2. Describe how limiting factors can affect the organisms in a population.

3. Explain the difference between a habitatand a niche.

4. Describe and give an example of two symbiotic relationships that occur amongpopulations in a community.

5. Think Critically A parasite can obtainfood only from its host. Most parasitesweaken but do not kill their hosts. Why?

6. Drawing Conclusions Explain how soundcould be used to relate the size of the cricket population in one field to the cricket population in another field. For more help, refer to the Science Skill Handbook.

7. Solving One-Step Equations A 15-m2

wooded area has the following: 30 ferns, 150grass plants, and 6 oak trees. What is the popula-tion density per m2 of each species? For morehelp, refer to the Math Skill Handbook.


Predation One way that populationsize is regulated is by predation (prih DAYshun). Predation is the act of one organ-ism hunting, killing, and feeding onanother organism. Owls are predators ofmice, as shown in Figure 16. Mice aretheir prey. Predators are biotic factors thatlimit the size of the prey population.Availability of prey is a biotic factor thatcan limit the size of the predator popula-tion. Because predators are more likely tocapture old, ill, or young prey, thestrongest individuals in the prey popula-tion are the ones that manage to repro-duce. This improves the prey populationover several generations.

Habitats and Niches In a commu-nity, every species plays a particular role.For example, some are producers andsome are consumers. Each also has a par-ticular place to live. The role, or job, of an organism in theecosystem is called its niche (NICH). What a species eats, how itgets its food, and how it interacts with other organisms are allparts of its niche. The place where an organism lives is called itshabitat. For example, an earthworm’s habitat is soil. An earth-worm’s niche includes loosening, aerating, and enriching thesoil.

Figure 16 Owls use their keen senses ofsight and hearing to hunt formice in the dark.

Matter and EnergyS E C T I O N

Energy Flow Through EcosystemsLife on Earth is not simply a collection of independent

organisms. Even organisms that seem to spend most of theirtime alone interact with other members of their species. Theyalso interact with members of other species. Most of the interac-tions among members of different species occur when oneorganism feeds on another. Food contains nutrients and energyneeded for survival. When one organism is food for anotherorganism, some of the energy in the first organism (the food) istransferred to the second organism (the eater).

Producers are organisms that take in and use energy fromthe Sun or some other source to produce food. Some use theSun’s energy for photosynthesis to produce carbohydrates. Forexample, plants, algae, and some one-celled, photosyntheticorganisms are producers. Consumers are organisms that take inenergy when they feed on producers or other consumers. Thetransfer of energy does not end there. When organisms die,other organisms called decomposers, as shown in Figure 17,take in energy as they break down the remains of organisms.This movement of energy through a community can be dia-grammed as a food chain or a food web.

Food Chains A food chain, as shown in Figure 18, is amodel, a simple way of showing how energy, in the form offood, passes from one organism to another. When drawing afood chain, arrows between organisms indicate the direction

of energy transfer. An example of a pond foodchain follows.

small water plants → insects → bluegill → bass

Food chains usually have three or four links.This is because the available energy decreasesfrom one link to the next link. At each transfer of energy, a portion of the energy is lost as heatdue to the activities of the organisms. In a foodchain, the amount of energy left for the last linkis only a small portion of the energy in the first link.

■ Explain the difference between afood chain and a food web.

■ Describe how energy flowsthrough ecosystems.

■ Examine how materials such aswater, carbon, and nitrogen areused repeatedly.

Vocabularyfood chain water cyclefood web

You are dependent upon the recy-cling of matter and the transfer ofenergy for survival.

Figure 17 These mushrooms are decom-posers. They obtain neededenergy for life when they breakdown organic material.

228

In nature, energy in foodpasses from one organism to another in a sequence

known as a food chain. All livingthings are linked in food chains,and there are millions of differ-ent chains in the world. Eachchain is made up of organisms in a community. The photo-graphs here show a food chain in a North Americanmeadow community.

The second link of a food chain is usually an herbivore like thisgrasshopper. Herbivores are animalsthat feed only on producers.

B

The third link of this food chain is acarnivore, an animalthat feeds on otheranimals. This wood-house toad feeds ongrasshoppers.

C

The last link in many food chains is a top carnivore, an animal that feeds onother animals, including other carnivores.This great horned owl is a top carnivore.

E

The first link inany food chain is aproducer—in thiscase, grass. Grassgets its energyfrom sunlight.

A

The fourth link of this food chain is a garter snake, whichfeeds on toads.

D

VISUALIZING A FOOD CHAIN

Figure 18

SECTION 3 Matter and Energy 229

Food Webs Food chains are too simple to describe the manyinteractions among organisms in an ecosystem. A food web is aseries of overlapping food chains that exist in an ecosystem. Afood web provides a more complete model of the way energymoves through an ecosystem. They also are more accurate mod-els because food webs show how many organisms are part ofmore than one food chain in an ecosystem.

Humans are a part of many different food webs. Most peo-ple eat foods from several different levels of a food chain. Everytime you eat a hamburger, an apple, or a tuna fish sandwich, youhave become a link in a food web. Can you picture the steps inthe food web that led to the food in your lunch?

How do changes in Antarctic food webs affect populations?

Problem-Solving Activity


How would changes in any of these popula-tions affect the other populations?

Identifying the ProblemWorldwide, the hunting of baleen whales

has been illegal since 1986. It is hoped thatthe baleen whale population will increase.How will an increase in the whale popula-tion affect this food web?

Solving the Problem1. Populations of seals, penguins, and krill-

eating fish increased in size as popula-tions of baleen whales declined. Explainwhy this occurred.

2. What might happen if the number ofbaleen whales increases but the amountof krill does not?

The food webs in the icy Antarctic Oceanare based on phytoplankton, which are

microscopic algae that float near the water’ssurface. The algae are eaten by tiny, shrimp-like krill, which are consumed by baleenwhales, squid, and fish. Toothed whales,seals, and penguins eat the fish and squid.

Ecological Pyramids Most of the energy in the biospherecomes from the Sun. Producers take in and transform only asmall part of the energy that reaches Earth’s surface. When anherbivore eats a plant, some of the energy in the plant passes tothe herbivore. However, most of it is given off into the atmo-sphere as heat. The same thing happens when a carnivore eats aherbivore. An ecological pyramid models the number of organ-isms at each level of a food chain. The bottom of an ecologicalpyramid represents the producers of an ecosystem. The rest ofthe levels represent successive consumers.

What is an ecological pyramid?

Energy Pyramid The flow of energy from grass to the hawkin Figure 19 can be illustrated by an energy pyramid. An energypyramid compares the energy available at each level of the foodchain in an ecosystem. Just as most food chains have three orfour links, a pyramid of energy usually has three or four levels.Only about ten percent of the energy at each level of the pyra-mid is available to the next level. By the time the top level isreached, the amount of energy available is greatly reduced.


Figure 19An energy pyramid illustratesthat available energy decreasesat each successive feeding step.Why doesn’t an energy pyramidhave more levels?

Certain bacteria take inenergy through a processcalled chemosynthesis. Inchemosynthesis, the bac-teria produce food usingthe energy in chemicalcompounds. In your Science Journal predictwhere these bacteria are found.

Condensation Precipitation

Runoff

Evaporation

Transpiration

Figure 20A water molecule that falls asrain can follow several pathsthrough the water cycle.How many of these paths can you identify in this diagram?

Modeling the Water CycleProcedure 1. With a marker, make a line

halfway up on a plastic cup.Fill the cup to the mark withwater.

2. Cover the top with plasticwrap and secure it with arubber band or tape.

3. Put the cup in direct sun-light. Observe the cup forthree days. Record yourobservations.

4. Remove the plastic wrapand observe the cup forseven more days.

Analysis1. What parts of the water

cycle did you observe during this activity?

2. How did the water level inthe cup change after theplastic wrap was removed?

232

The Cycles of Matter The energy available as food is constantly renewed by plants

using sunlight. However, think about the matter that makes upthe bodies of living organisms. The law of conservation of massstates that matter on Earth is never lost or gained. It is used overand over again. In other words, it is recycled. The carbon atomsin your body might have been on Earth since the planet formedbillions of years ago. They have been recycled billions of times.Many important materials that make up your body cyclethrough the environment. Some of these materials are water,carbon, and nitrogen.

Water Cycle Water molecules onEarth constantly rise into the atmo-sphere, fall to Earth, and soak into

the ground or flow into rivers and oceans. The water cycleinvolves the processes of evaporation, condensation, and precip-itation.

Heat from the Sun causes water on Earth’s surface to evapo-rate, or change from a liquid to a gas, and rise into the atmo-sphere as water vapor. As the water vapor rises, it encounterscolder and colder air and the molecules of water vapor slowdown. Eventually, the water vapor changes back into tinydroplets of water. It condenses, or changes from a gas to a liquid.These water droplets clump together to form clouds. When thedroplets become large and heavy enough, they fall back to Earthas rain or other precipitation. This process is illustrated in Figure 20.

Other Cycles inNature What doyou have in commonwith all organisms? Allorganisms containcarbon. Earth’s atmo-sphere contains about0.03 percent carbon inthe form of carbondioxide gas. Themovement of carbonthrough Earth’s bio-sphere is called thecarbon cycle, as shownin Figure 21.

Nitrogen is an ele-ment used by organ-isms to make proteinsand nucleic acids. The nitrogencycle begins with the transfer ofnitrogen from the atmosphere toproducers then to consumers. Thenitrogen then moves back to the atmosphere or directly intoproducers again.

Phosphorus, sulfur, and other elements needed by livingorganisms also are used and returned to the environment. Justas you recycle aluminum, glass, and paper products, the materi-als that organisms need to live are recycled continuously in thebiosphere.


Section Assessment

1. Compare a food chain and a food web.

2. What are the differences among producers,consumers, and decomposers?

3. What is an energy pyramid?

4. How does carbon flow through eco-systems?

5. Think Critically Use your knowledge offood chains and the energy pyramid toexplain why fewer lions than gazelles liveon the African plains.

6. Classifying Look at the food chain in Figure18. Classify each organism as a producer or aconsumer. For more help, refer to the ScienceSkill Handbook.

7. Communicating In your Science Journal,write a short essay about how the water cycle,carbon cycle, and nitrogen cycle are importantto living organisms. For more help, refer to theScience Skill Handbook.

Figure 21Carbon can follow several differ-ent paths through the carboncycle. Some carbon is stored inEarth’s biomass.

Plants remove carbon dioxide from the air and use it to make carbohydrates.

The carbohydrates are eaten and used by other organisms.

The carbon from the carbohydrates is returned to the atmosphere through respiration, combustion, and decay.

After the carbon is returned to the atmosphere, thecycle begins again.

Organisms depend upon many biotic and abiotic factors in their environment tosurvive. When these factors are limited or are not available, it can affect an

organism’s survival. By experimenting with some of these limiting factors, you willsee how organisms depend on all parts of their environment.

Recognize the ProblemHow do abiotic factors such as light, water, and temperature affect the germinationof seeds?

Form a HypothesisBased on what you have learned about limiting factors, make a hypothesis about how one specific abiotic factor might affect the germination of a bean seed. Be sure toconsider factors that you can change easily.

Identifying a Limiting Factor

Safety Precautions

Wash hands after handling soil and seeds.

Goals■ Observe the effects of an abiotic

factor on the germination andgrowth of bean seedlings.

■ Design an experiment that demon-strates whether or not a specific abiotic factor limits the germinationof bean seeds.

Possible Materialsbean seedssmall planting containerssoilwaterlabeltrowel *spoonaluminum foilsunny window *other light sourcerefrigerator or oven*Alternate materials

234

Test Your Hypothesis

Analyze Your Data

Draw Conclusions

Do1. Make sure your teacher approves

your plan before you start.

2. Carry out the experiment accordingto the approved plan.

3. While the experiment is going on,record any observations that youmake and complete the data tablein your Science Journal.

Plan1. As a group, agree upon and write

out a hypothesis statement.

2. Decide on a way to test your group’s hypothesis. Keep availablematerials in mind as you plan yourprocedure. List your materials.

3. Design a data table in your ScienceJournal for recording data.

4. Remember to test only one variableat a time and use suitable controls.

5. Read over your entire experiment to make sure that all steps are inlogical order.

6. Identify any constants, variables,and controls in your experiment.

7. Be sure the factor that you will testis measurable.

3. Graph your results in a bar graphthat compares the number of beanseeds that germinated in the exper-imental container with the numberof seeds that germinated in thecontrol container.

1. Compare the results of this experi-ment with those of other groups inyour class.

2. Infer how the abiotic factor youtested affected the germination ofbean seeds.

1. Identify which factor had thegreatest effect on the germinationof the seeds.

2. Determine whether or not youcould change more than one factorin this experiment and still havegermination of seeds.

ACTIVITY 235

Write a set of instructions that could be includedon a packet of this type of seeds. Describe thebest conditions for seed germination.

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Science & Language ArtsandandandScience Language Arts

Respond to the ReadingRespond to the Reading

1. From reading thispassage, can youguess the occupationof the narrator?

2. Describe the relation-ship between peopleand animals in thispassage.

3. What words does the author use toindicate that horsesare intelligent?

Animals give us their constant, unjaded1 faces andwe burden them with our bodies and civilizedordeals. We’re both humbled by and imperious2

with them. We’re comrades who save each other’s lives.The horse we pulled from a boghole this morning buckedsomeone off later in the day; one stock dog refuses to worksheep, while another brings back a calf we had overlooked.. . . What’s stubborn, secretive, dumb, and keen3 in usbumps up against those same qualities in them. . . .

Living with animals makes us redefine our ideas aboutintelligence. Horses are as mischievous as they are depend-able. Stupid enough to let us use them, they are cunningenough to catch us off guard. . . .

We pay for their loyalty; They can be willful, hard tocatch, dangerous to shoe and buck on frosty mornings. Inturn, they’ll work themselves into a lather cutting cows,

not for the praise they’llget but for the simpleglory of outdodging a calfor catching up with anerrant steer. . . .

1 Jaded means “to be weary with fatigue,” so

unjaded means “not to be weary with fatigue.”2 domineering or overbearing3 intellectually smart or sharp

The Solace of Open Spacesa novel by Gretel Ehrlich


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Informative Writing Write ashort passage about an experi-ence you have had with a pet. Inyour writing, reflect on how youand the pet are alike and depend-ent upon each other. Put yourselffirmly in the story without over-using the word I.

andandandLinking Science Linking Science

Dave Garza works to keep horses healthy. Dave spends about 20 percent of his workday in his clinic. He goes there first thing in themorning to perform surgeries and take care of horses that have beenbrought to him. The rest of the day, he drives to local farms to examine patients. Dave vaccinates horses against rabies, the flu, andthe encephalitis virus. He gives them tetanus shots and medication toprevent worms. He also cares for their teeth, replaces their shoes,and helps them deliver their foals in the spring.

To learn more about careers in veterinary medi-cine, visit the Glencoe Science Web site at science.glencoe.com.

Large-Animal Veterinarian�

CareerCareer ConnectionConnection

Understanding LiteratureInformative Writing The passage that you have justread is from a work of nonfiction and is based onfacts. The passage is informative because it describesthe real relationship between people and animals on aranch in Wyoming. The author speaks from her ownpoint of view, not from the point of view of a disinter-ested party. She uses her own experience to explain toreaders that animals and people depend on each otherfor survival. For example, she writes, “Living with ani-mals makes us redefine our ideas about intelligence.”The language puts her firmly in the story—she is notonly telling the story, but living it, too. How might thisstory have been different if it had been told from thepoint of view of a visiting journalist?

Science Connection Animals and ranchers are clearlydependent on each other. Ranchers provide nutritionand shelter for animals on the ranch and, in turn, ani-mals provide food and perform work for the ranchers.You might consider the relationship between horsesand ranchers to be a symbiotic one. Symbiosis (sihmbee OH sus) is any close interaction among two ormore different species.

Informative Writing

SCIENCE AND LANGUAGE ARTS 237


238 CHAPTER STUDY GUIDE

4. The place where anorganism lives is itshabitat, and its role inthe environment is itsniche. How could twosimilar species of birdslive in the same area andnest in the same tree with-out occupying the same niche?

Section 3 Matter and Energy1. Food chains and food webs are models

that describe the feeding relationshipsamong organisms in a community.

2. At each level of a food chain, organisms lose energy as heat. Energy on Earth isrenewed constantly by sunlight.

3. An ecological pyramid models the number of organisms at each level of a food chain in an ecosystem.Why is each level of this energy pyramid smaller than the one below it?

4. Matter on Earth is never lost or gained. It isused over and over again, or recycled.

Section 1 The Environment1. Ecology is the study of interactions among

organisms and their environment.

2. The nonliving features of the environmentare abiotic factors, and the organisms in theenvironment are biotic factors.

3. Populations and communities make up anecosystem. What populations and communi-ties might be present in this ecosystem?

4. The region of Earth and its atmosphere inwhich all organisms live is the biosphere.

Section 2 Interactions Among LivingOrganisms

1. Characteristics that can describe popula-tions include size, spacing, and density.

2. Any biotic or abiotic factor that limits thenumber of individuals in a population is alimiting factor.

3. A close relationship between two or morespecies is a symbiotic relationship. A symbi-otic relationship that benefits both speciesis called mutualism. A relationship in whichone species benefits and the other is un-affected is called commensalism.

Using your Foldable,explain the cause andeffect relationship

between specific abiotic and biotic organismsaround you.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter Study GuideChapter 88

CHAPTER STUDY GUIDE 239

Vocabulary Wordsa. abiotic factor i. habitatb. biosphere j. limiting factorc. biotic factor k. niched. community l. populatione. ecology m. population densityf. ecosystem n. symbiosisg. food chain o. water cycleh. food web

Using VocabularyReplace the underlined words with the correct

vocabulary words.

1. A(n) abiotic factor is any living thing in theenvironment.

2. A series of overlapping food chains makesup a(n) nitrogen cycle.

3. The size of a population that occupies anarea of definite size is its carrying capacity.

4. Where an organism lives in an ecosystem isits niche.

5. The part of Earth that supports life is thelimiting factor.

6. Any close relationship between two or morespecies is habitat.

Use tables to organize ideas. For example, putthe levels of biological organization in a table.Tables help you review concepts quickly.

Study Tip

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Study GuideChapter

Complete the following concept mapon the biosphere.

88

Choose the word or phrase that best answersthe question.

1. Which of the following is NOT cycled in thebiosphere?A) nitrogen C) waterB) soil D) carbon

2. What are coral reefs, forests, and pondsexamples of?A) niches C) populationsB) habitats D) ecosystems

3. What is made up of all populations in anarea?A) niche C) communityB) habitat D) ecosystem

4. What is the term for the total number ofindividuals in a population occupying acertain area?A) clumping C) spacingB) size D) density

5. Which of the following is an example of aproducer?A) wolf C) treeB) frog D) rabbit

6. Which level of the food chain has the mostenergy? A) consumer C) decomposersB) herbivores D) producers

7. What is a relationship called in which oneorganism is helped and the other isharmed?A) mutualism C) commensalismB) parasitism D) consumer

8. Which of the following is a model thatshows the amount of energy available as itflows through an ecosystem?A) niche C) carrying capacityB) energy pyramid D) food chain

9. Which of the following is a biotic factor?A) animals C) sunlightB) air D) soil

10. What are all of the individuals of onespecies that live in the same area at the sametime called?A) community C) biosphereB) population D) organism

11. What are two different populations thatmight be present in a desert biome? Twodifferent ecosystems? Explain.

12. Why are viruses considered parasites?

13. What does carrying capacity have to dowith whether or not a population reachesits biotic potential?

14. Why are decomposers vital to the cycling ofmatter in an ecosystem?

15. Write a paragraph that describes your ownhabitat and niche.

16. Classifying Classify the following as theresult of either evaporation or condensa-tion.a. A puddle disappears after a rainstorm.b. Rain falls.c. A lake becomes shallower.d. Clouds form.

17. Concept Mapping Use the following infor-mation to draw a food web of organismsliving in a goldenrod field. Aphids eat gold-enrod sap, bees eat goldenrod nectar, beetleseat goldenrod pollen and goldenrod leaves,stinkbugs eat beetles, spiders eat aphids, andassassin bugs eat bees.

240 CHAPTER ASSESSMENT

AssessmentChapter 88

CHAPTER ASSESSMENT 241

18. Making and UsingGraphs Use the fol-lowing data to graphthe population den-sity of a deer popula-tion over the years.Plot the number ofdeer on the y-axisand years on the x-axis. Predict whatmight have hap-pened to cause thechanges in the size of the population.

19. Recording Observations A home aquariumcontains water, an air pump, a light, algae, agoldfish, and algae-eating snails. What arethe abiotic factors in this environment?

20. Comparing and Contrasting Compare andcontrast the role of producers, consumers,and decomposers in an ecosystem.

21. Poster Use your own observations or theresults of library research to develop a foodweb for a nearby park, pond, or otherecosystem. Make a poster display illustrat-ing the food web.

22. Oral Presentation Research the steps in thephosphorous cycle. Find out what rolephosphorus plays in the growth of algae inponds and lakes. Present your findings tothe class.

Year Deer Per 400Hectares

1905 5.7

1915 35.7

1920 142.9

1925 85.7

1935 25.7

Arizona Deer Population

Go to the Glencoe Science Web site at science.glencoe.com or use theGlencoe Science CD-ROM for additionalchapter assessment.

TECHNOLOGY

AssessmentChapter

Biologists want to estimate the totalnumber of fish in a lake. They plan to towa sampling device from one side of thelake to the other a single time. They dis-cuss the sampling strategies shown below.

Use the diagrams to answer the following questions.

1. Which strategy is likely to provide themost accurate estimate of the numberof fish in the lake?A) diagram 1 C) diagram 3B) diagram 2 D) diagram 4

2. How can the biologists improve theirinvestigation?F) tow the sampling device very

quicklyG) tow the sampling device very slowlyH) tow the sampling device more then

onceJ) tow the sampling device around the

edge of the lake

AssessmentChapter

1 3

42

Test Practice

88


Documents

Unit 3 Science (Glencoe Red 2002)