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Chapter 3 The Biosphere

A tawny owl prepares to seize a mouse. The mouse is carrying a berry in its mouth as it runs along a fallen,moss-covered tree trunk. The owl, the mouse, the tree trunk, and the moss are all members of this forest ecosystem.

How do organisms affect one another's survival?

Procedure

Make a list of all the types of organisms, including plants, humans, insects, and soon, that you have seen near your home or school.

1.

Make a diagram that shows how the organisms on your list interact with oneanother.

2.

Think About It

Classifying Which organisms on your list provide energy or nutrients to theothers?

1.

Predicting What would you expect to happen if all the plants on your diagramdied? Explain your answer.

2.

Asking Questions Why is it difficult to make accurate predictions aboutchanges in communities of organisms?

3.

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Key ConceptsWhat different levels oforganization do ecologistsstudy?What methods are used tostudy ecology?

VocabularyecologybiospherespeciespopulationcommunityecosystembiomeReading Strategy: AskingQuestions Before you read,rewrite the headings in thissection as how, what, or whyquestions about ecology. Then,as you read, write briefanswers to your questions.

3-1 What Is Ecology?“Floods hit Texas!” “Wildfires char three states!”“Drought withers Florida!” Such news often flashesacross television screens, newspapers, and theInternet. We are fascinated and frightened by thesenatural events, but there are other stories, as well.Some tell of projects to restore wetlands in southernFlorida and along the Mississippi River for thepurpose of controlling floods and droughts. Othersreport on improvements in air and water quality as aresult of changes in the gasoline that we put in ourcars. Like all organisms, we interact with ourenvironment. To understand these interactions betterand to learn how to control them, we turn to thescience called ecology.

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3-1 What Is Ecology? (continued)Interactions and Interdependence

Ecology (ee-KAHL-uh-jee) is the scientific study ofinteractions among organisms and between organisms andtheir environment, or surroundings. The word ecology wascoined in 1866 by the German biologist Ernst Haeckel.Haeckel based this term on the Greek word oikos, meaninghouse, which is also the root of the word economy. Haeckelsaw the living world as a household with an economy inwhich each organism plays a role.

Nature's “houses” come in many sizes—from single cells tothe entire planet. The largest of these houses is called thebiosphere. The biosphere contains the combined portions ofthe planet in which all of life exists, including land, water,and air, or atmosphere. It extends from about 8 kilometersabove Earth's surface to as far as 11 kilometers below thesurface of the ocean.

Interactions within the biosphere produce a web of inter-dependence between organisms and the environment inwhich they live. Whether it occurs on top of a glacier, in aforest, or deep within an ocean trench, the interdependence oflife on Earth contributes to an ever-changing, or dynamic,biosphere.

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3-1 What Is Ecology? (continued)Levels of Organization

To understand relationships within the biosphere,ecologists ask questions about events and organisms thatrange in complexity from a single individual to the entirebiosphere. The many levels of organization that ecologistsstudy are shown in the figure to the right.

Levels of Organization

Some ecologists study interactions between a particular kindof organism and its surroundings. Such studies focus on thespecies level. A species is a group of organisms so similar toone another that they can breed and produce fertile offspring.Other ecologists study populations, or groups of individualsthat belong to the same species and live in the same area.Still other ecologists study communities, or assemblages ofdifferent populations that live together in a defined area.

Ecologists may study a particular ecosystem. An ecosystemis a collection of all the organisms that live in a particularplace, together with their nonliving, or physical,environment. Larger systems called biomes are also studiedby teams of ecologists. A biome is a group of ecosystemsthat have the same climate and similar dominantcommunities. The highest level of organization thatecologists study is the entire biosphere itself.

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3-1 What Is Ecology? (continued)Ecological Methods

Ecologists use a wide range of tools and techniques to studythe living world. Some use binoculars and field guides toassess changes in plant and wildlife communities. Others usestudies of DNA to identify bacteria in the mud of coastalmarshes. Still others use radio tags to track migrating wildlifeor use data gathered by satellites.

Regardless of the tools they use, scientists conductmodern ecological research using three basic approaches:observing, experimenting, and modeling. All of theseapproaches rely on the application of scientific methodsto guide ecological inquiry.

Observing Observing is often the first step in askingecological questions. Some observations are simple: Whatspecies live here? How many individuals of each species arethere? Other observations are more complex and may formthe first step in designing experiments and models.

Experimenting Experiments can be used to testhypotheses. An ecologist may set up an artificialenvironment in a laboratory to imitate and manipulateconditions that organisms would encounter in the naturalworld. Other experiments are conducted within naturalecosystems.

Modeling Many ecological phenomena occur over longperiods of time or on such large spatial scales that they aredifficult to study. Ecologists make models to gain insight intocomplex phenomena such as the effects of global warmingon ecosystems. Many ecological models consist ofmathematical formulas based on data collected throughobservation and experimentation. The predictions made byecological models are often tested by further observationsand experiments.

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3-1 What Is Ecology?

To answer the questions below electronically, click on the My Notes icon above.

1. Key Concept List the six different levels of organization that ecologists study,in order from smallest to largest.

2. Key Concept Describe the three basic methods of ecological research. 3. Identify two ways in which you interact every day with each of the three parts of the

biosphere—land, water, and air. 4. Critical Thinking Applying Concepts Suppose you wanted to know if the water

in a certain stream is safe to drink. Which ecological method(s) would you choose,and why?

5. Critical Thinking Applying Concepts Give an example of an ecologicalphenomenon that could be studied by modeling. Explain why modeling would beuseful.

Creating a TableRefer to Levels of Organization, which shows the various levels of organization thatecologists study. In a table, provide examples of the ecological levels where youlive—individuals, populations, communities, and ecosystems—that could be studied byecologists. Hint: You may wish to use library resources or the Internet.

References

Exploring Ecology From Space

Modern research in global ecology would not be possible if all its tools wereearthbound. Studies on a planetary scale require enormous data-gathering networks.Through a process called remote sensing, satellites extend the range of information thatecologists can collect within the biosphere.

Remote-sensing satellites are fitted with optical sensors that can scan several bands ofthe electromagnetic spectrum and convert those bands into electrical signals. Thesignals are run through a computer and converted into digital values, which are used toconstruct an image.

Remote sensing provides detailed images of essentially every square meter of Earth'ssurface. How else could scientists view all the world's lakes and oceans to see whereconcentrations of algae are the highest? Or view areas of destroyed forests in places likethe Amazon Basin or northern Russia?

Global Change

The false-color image below was assembled from data gathered by NASA'sSea-viewing Wide Field-of-view Sensor (SeaWiFS) Project. The project's goal is tostudy factors that affect global change and to assess the oceans' role in the global carboncycle, as well as other chemical cycles. The different ocean colors indicate varyingconcentrations of microscopic algae. Blue represents the least amount of algae, and redrepresents the highest amount. On land, the dark green areas have the most vegetation,and gold land areas have the least.

Rain Forest Destruction

Satellite images that show the presence or absence of vegetation are useful in studyingthe effects of human activity on natural ecosystems. The two images shown below,taken 26 years apart, show the same tract of land in a Brazilian rain forest. Red areasshow undisturbed forest, and whitish areas show places where trees have been cut andcleared. Note the “fishbone” pattern of vegetation clearing. This pattern occurs becausecutting of forests typically begins along existing roads and rivers and then spreads outas new roads and paths are cut.

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Key ConceptsWhere does the energy forlife processes come from?How does energy flowthrough living systems?How efficient is thetransfer of energy amongorganisms in anecosystem?

Vocabularyautotrophproducerphotosynthesischemosynthesisheterotrophconsumerherbivorecarnivoreomnivoredetritivoredecomposerfood chainfood webtrophic levelecological pyramidbiomassReading Strategy:Building Vocabulary Asyou read, make notes about themeaning of each term in thelist above and how it relates toenergy flow in the biosphere.Then, draw a concept map toshow the relationships amongthese terms.

3-2 Energy FlowAt the core of every organism's interaction with theenvironment is its need for energy to power life'sprocesses. Consider, for example, the energy thatants use to carry objects many times their size or theenergy that birds use to migrate thousands of miles.Think about the energy that you need to get out ofbed in the morning! The flow of energy through anecosystem is one of the most important factors thatdetermines the system's capacity to sustain life.

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3-2 Energy Flow (continued)Producers

Without a constant input of energy, living systems cannotfunction. Sunlight is the main energy source for life onEarth. Of all the sun's energy that reaches Earth's surface,only a small amount—less than 1 percent—is used by livingthings. This seemingly small amount is enough to produce asmuch as 3.5 kilograms of living tissue per square meter ayear in some tropical forests.

In a few ecosystems, some organisms obtain energy from asource other than sunlight. Some types of organismsrely on the energy stored in inorganic chemicalcompounds. For instance, mineral water that flowsunderground or boils out of hot springs and undersea vents isloaded with chemical energy.

Only plants, some algae, and certain bacteria can captureenergy from sunlight or chemicals and use that energy toproduce food. These organisms are called autotrophs.Autotrophs use energy from the environment to fuel theassembly of simple inorganic compounds into complexorganic molecules. These organic molecules combine andrecombine to produce living tissue. Because they make theirown food, autotrophs, like the kelp shown at right, are alsocalled producers. Both types of producers—those thatcapture energy from sunlight and those that capture chemicalenergy—are essential to the flow of energy through thebiosphere.

Kelp Forest

Energy From the Sun The best-known autotrophs arethose that harness solar energy through a process known asphotosynthesis. During photosynthesis, these autotrophs uselight energy to power chemical reactions that convert carbondioxide and water into oxygen and energy-rich carbohydratessuch as sugars and starches. This process, shown in the figureat right (top), is responsible for adding oxygen to—andremoving carbon dioxide from—Earth's atmosphere. In fact,were it not for photosynthetic autotrophs, the air would notcontain enough oxygen for you to breathe!

Photosynthesis andChemosynthesis

On land, plants are the main autotrophs. In freshwaterecosystems and in the sunlit upper layers of the ocean, algaeare the main autotrophs. Photosynthetic bacteria, the mostcommon of which are the cyanobacteria (sy-an-oh-bak-TEER-ee-uh), are important in certain wet ecosystems suchas tidal flats and salt marshes.

Life Without Light Although plants are the most visibleand best-known autotrophs, some autotrophs can produce

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3-2 Energy Flow (continued)Consumers

Many organisms—including animals, fungi, and manybacteria—cannot harness energy directly from the physicalenvironment as autotrophs do. The only way these organismscan acquire energy is from other organisms. Organisms thatrely on other organisms for their energy and food supply arecalled heterotrophs (HET-ur-oh-trohfs). Heterotrophs arealso called consumers.

There are many different types of heterotrophs. Herbivoresobtain energy by eating only plants. Some herbivores arecows, caterpillars, and deer. Carnivores, including snakes,dogs, and owls, eat animals. Humans, bears, crows, and otheromnivores eat both plants and animals. Detritivores(dee-TRYT-uh-vawrz), such as mites, earthworms, snails,and crabs, feed on plant and animal remains and other deadmatter, collectively called detritus. Another important groupof heterotrophs, called decomposers, breaks down organicmatter. Bacteria and fungi are decomposers.

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3-2 Energy Flow (continued)Feeding Relationships

What happens to the energy in an ecosystem when oneorganism eats another? That energy moves along a one-waypath. Energy flows through an ecosystem in onedirection, from the sun or inorganic compounds toautotrophs (producers) and then to various heterotrophs(consumers). The relationships between producers andconsumers connect organisms into feeding networks basedon who eats whom.

Food Chains The energy stored by producers can bepassed through an ecosystem along a food chain, a series ofsteps in which organisms transfer energy by eating and beingeaten. For example, in a prairie ecosystem, a food chainmight consist of a producer, such as grass, that is fed upon bya herbivore, such as a grazing antelope. The herbivore is inturn fed upon by a carnivore, such as a coyote. In thissituation, the carnivore is only two steps removed from theproducer.

In some marine food chains, such as the one shown at right,the producers are microscopic algae that are eaten by verysmall organisms called zooplankton (zoh-oh-PLANK-tun).The zooplankton, in turn, are eaten by small fish, such asherring. The herring are eaten by squid, which are ultimatelyeaten by large fish, such as sharks. In this food chain, the topcarnivore is four steps removed from the producer.

A Marine Food Chain

Food Webs In most ecosystems, feeding relationships aremore complex than can be shown in a food chain. Consider,for example, the relationships in a salt marsh. Although someproducers—including marsh grass and other salt-tolerantplants—are eaten by water birds, grasshoppers, and otherherbivores, most producers complete their life cycles, thendie and decompose. Decomposers convert the dead plantmatter to detritus, which is eaten by detritivores, such assandhoppers. The detritivores are in turn eaten by smelt andother small fish. Some of those consumers will also eatdetritus directly. Add mice, larger fish, and hawks to thescenario, and feeding relationships can get very confusing!

When the feeding relationships among the various organismsin an ecosystem form a network of complex interactions,ecologists describe these relationships as a food web. A foodweb links all the food chains in an ecosystem together. Thefood web in the figure shown at right, for example, shows thefeeding relationships in a salt-marsh community.

A Salt-Marsh Food Web

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3-2 Energy Flow (continued)Ecological Pyramids

The amount of energy or matter in an ecosystem can berepresented by an ecological pyramid. An ecologicalpyramid is a diagram that shows the relative amounts ofenergy or matter contained within each trophic level in afood chain or food web. Ecologists recognize three differenttypes of ecological pyramids: energy pyramids, biomasspyramids, and pyramids of numbers. The figure at rightshows an example of each type.

Ecological Pyramids

Energy Pyramid Theoretically, there is no limit to thenumber of trophic levels that a food chain can support. Butthere is one hitch. Only part of the energy that is stored inone trophic level is passed on to the next level. This isbecause organisms use much of the energy that they consumefor life processes, such as respiration, movement, andreproduction. Some of the remaining energy is released intothe environment as heat. Only about 10 percent of theenergy available within one trophic level is transferred toorganisms at the next trophic level. For instance, one tenthof the solar energy captured by grasses ends up stored in thetissues of cows and other grazers. Only one tenth of thatenergy—10 percent of 10 percent, or 1 percent total—istransferred to the humans that eat the cows. Thus, the morelevels that exist between a producer and a top-level consumerin an ecosystem, the less energy that remains from theoriginal amount.

For: Links on energypyramidsVisit: www.SciLinks.orgWeb Code: cbn-2032

Biomass Pyramid The total amount of living tissue withina given trophic level is called biomass. Biomass is usuallyexpressed in terms of grams of organic matter per unit area.A biomass pyramid represents the amount of potential foodavailable for each trophic level in an ecosystem.

Pyramid of Numbers Ecological pyramids can also bebased on the numbers of individual organisms at each trophiclevel. For some ecosystems, such as the meadow shown inEcological Pyramids, the shape of the pyramid of numbersis the same as that of the energy and biomass pyramids. This,however, is not always the case. In most forests, for example,there are fewer producers than there are consumers. A singletree has a large amount of energy and biomass, but it is onlyone organism. Many insects live in the tree, but they haveless energy and biomass. Thus, a pyramid of numbers for aforest ecosystem would not resemble a typical pyramid at all!

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3-2 Energy Flow

To answer the questions below electronically, click on the My Notes icon above.

1. Key Concept What are the two main forms of energy that power livingsystems?

2. Key Concept Briefly describe the flow of energy among organisms in anecosystem.

3. Key Concept What proportion of energy is transferred from one trophic levelto the next in an ecosystem?

4. Explain the relationships in this food chain: omnivore, herbivore, and autotroph.

5. Critical Thinking Calculating Draw an energy pyramid for a five-step foodchain. If 100 percent of the energy is available at the first trophic level, whatpercentage of the total energy is available at the highest trophic level?

Descriptive WritingRefer to A Salt-Marsh Food Web , which shows a food web in a salt marsh. Chooseone of the food chains within this web. Then, write a paragraph describing the feedingrelationships among the organisms in the food chain. Hint: Use the terms producers,consumers, and decomposers in your description.

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Key ConceptsHow does matter moveamong the living andnonliving parts of anecosystem?How are nutrientsimportant in livingsystems?

Vocabularybiogeochemical cycleevaporationtranspirationnutrientnitrogen fixationdenitrificationprimary productivitylimiting nutrientalgal bloomReading Strategy: UsingVisuals Before you read,preview the cycles shown inthese figures: The WaterCycle, The Carbon Cycle,The Nitrogen Cycle, and ThePhosphorus Cycle. Noticehow each diagram is similar toor different from the others. Asyou read, take notes on howeach chemical moves throughthe biosphere.

3-3 Cycles of MatterEnergy is crucial to an ecosystem. But all organismsneed more than energy to survive. They also needwater, minerals, and other life-sustainingcompounds. In most organisms, more than 95percent of the body is made up of just four elements:oxygen, carbon, hydrogen, and nitrogen. Althoughthese four elements are common on Earth,organisms cannot use them unless the elements arein a chemical form that cells can take up.

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3-3 Cycles of Matter (continued)Recycling in the Biosphere

Energy and matter move through the biosphere verydifferently. Unlike the one-way flow of energy, matteris recycled within and between ecosystems. Elements,chemical compounds, and other forms of matter are passedfrom one organism to another and from one part of thebiosphere to another through biogeochemical cycles. As thelong word suggests, biogeochemical cycles connectbiological, geological, and chemical aspects of the biosphere.

Matter can cycle through the biosphere because biologicalsystems do not use up matter, they transform it. The matter isassembled into living tissue or passed out of the body aswaste products. Imagine, for a moment, that you are a carbonatom in a molecule of carbon dioxide floating in the air of awetland. The leaf of a blueberry bush absorbs you duringphotosynthesis. You become part of a carbohydrate moleculeand are used to make fruit. The fruit is eaten by a caribou,and within a few hours, you are passed out of the animal'sbody. You are soon swallowed by a dung beetle, thencombined into the body tissue of a hungry shrew, which isthen eaten by an owl. Finally, you are released into theatmosphere once again when the owl exhales. Then, the cyclestarts again.

Simply put, biogeochemical cycles pass the same moleculesaround again and again within the biosphere. Justthink—with every breath you take, you inhale hundreds ofthousands of oxygen atoms that might have been inhaled bydinosaurs millions of years ago!

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3-3 Cycles of Matter (continued)The Water Cycle

All living things require water to survive. Where does all thiswater come from? It moves between the ocean, atmosphere,and land. As the figure at right shows, water molecules enterthe atmosphere as water vapor, a gas, when they evaporatefrom the ocean or other bodies of water. The process bywhich water changes from liquid form to an atmospheric gasis called evaporation (ee-vap-uh-RAY-shun). Water can alsoenter the atmosphere by evaporating from the leaves ofplants in the process of transpiration (tran-spuh-RAY-shun).

The Water Cycle

During the day, the sun heats the atmosphere. As the warm,moist air rises, it cools. Eventually, the water vaporcondenses into tiny droplets that form clouds. When thedroplets become large enough, the water returns to Earth'ssurface in the form of precipitation—rain, snow, sleet, orhail.

On land, much of the precipitation runs along the surface ofthe ground until it enters a river or stream that carries therunoff back to an ocean or lake. Rain also seeps into the soil,some of it deeply enough to become ground water. Water inthe soil enters plants through the roots, and the water cyclebegins anew.

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3-3 Cycles of Matter (continued)Nutrient Cycles

The food you eat provides energy and chemicals that keepyou alive. All the chemical substances that an organismneeds to sustain life are its nutrients. Think of them as thebody's chemical “building blocks.” Primary producers, suchas plants, usually obtain nutrients in simple inorganic formsfrom their environment. Consumers obtain nutrients byeating other organisms. Every living organism needsnutrients to build tissues and carry out essential lifefunctions. Like water, nutrients are passed betweenorganisms and the environment through biogeochemicalcycles.

The carbon cycle, nitrogen cycle, and phosphorus cycle areespecially important. Note also that oxygen participates in allthese cycles by combining with these elements and cyclingwith them during various parts of their journey.

Cycles in Nature

The Carbon Cycle Carbon plays many roles. Carbon is akey ingredient of living tissue. In the form of calciumcarbonate (CaCO3), carbon is an important component ofanimal skeletons and is found in several kinds of rocks.Carbon and oxygen form carbon dioxide gas (CO2), animportant component of the atmosphere. Carbon dioxide istaken in by plants during photosynthesis and is given off byboth plants and animals during respiration. Four main typesof processes move carbon through its cycle:

Biological processes, such as photosynthesis,respiration, and decomposition, take up and releasecarbon and oxygen.Geochemical processes, such as erosion andvolcanic activity, release carbon dioxide to theatmosphere and oceans.Mixed biogeochemical processes, such as the burialand decomposition of dead organisms and theirconversion under pressure into coal and petroleum(fossil fuels), store carbon underground.Human activities, such as mining, cutting andburning forests, and burning fossil fuels, releasecarbon dioxide into the atmosphere.

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3-3 Cycles of Matter (continued)Nutrient Limitation

Ecologists are often interested in the primary productivityof an ecosystem, which is the rate at which organic matter iscreated by producers. One factor that controls the primaryproductivity of an ecosystem is the amount of availablenutrients. If a nutrient is in short supply, it will limit anorganism's growth. When an ecosystem is limited by a singlenutrient that is scarce or cycles very slowly, this substance iscalled a limiting nutrient.

Because they are well aware of this phenomenon, farmersapply fertilizers to their crops to boost their productivity.Fertilizers usually contain three important nutrients—nitrogen, phosphorus, and potassium. These nutrients helpplants grow larger and more quickly than they would inunfertilized soil.

The open oceans of the world can be considerednutrient-poor environments compared to the land. Sea watercontains at most only 0.00005 percent nitrogen, or 1/10,000of the amount typically found in soil. In the ocean and othersaltwater environments, nitrogen is often the limitingnutrient. In some areas of the ocean, however, silica or eveniron can be the limiting nutrient. In streams, lakes, andfreshwater environments, phosphorus is typically the limitingnutrient.

When an aquatic ecosystem receives a large input of alimiting nutrient—for example, runoff from heavily fertilizedfields—the result is often an immediate increase in theamount of algae and other producers. This result is called analgal bloom. Why do algal blooms occur? There are morenutrients available, so the producers can grow and reproducemore quickly. If there are not enough consumers to eat theexcess algae, conditions can become so favorable for growththat algae cover the surface of the water. Algal blooms cansometimes disrupt the equilibrium of an ecosystem.

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3-3 Cycles of Matter

To answer the questions below electronically, click on the My Notes icon above.

1. Key Concept How does the way that matter flows through an ecosystem differfrom the way that energy flows?

2. Key Concept Why do living organisms need nutrients? 3. Describe the path of nitrogen through its biogeochemical cycle. 4. Explain how a nutrient can be a limiting factor in an ecosystem. 5. Critical Thinking Predicting Based on your knowledge of the carbon cycle, what

do you think might happen if vast areas of forests are cleared? 6. Critical Thinking Applying Concepts Summarize the role of algal blooms in

disrupting the equilibrium in an aquatic ecosystem.

Making a FlowchartUse a flowchart to trace the flow of energy in the carbon cycle. Hint: You may wish torefer to The Carbon Cycle, especially to the labels Photosynthesis, Feeding,Respiration, and Decomposition. Also, you may want to refer to A Marine Food Chainin Section 3-2 for a description of energy flow in an ecosystem.

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Identifying a LimitingNutrientLimiting nutrients control the growth of organisms in many ecosystems. Excessnutrients can promote the growth of weeds, disease-causing bacteria, and otherundesirable organisms. In this investigation, you will determine whether phosphate is alimiting nutrient for the growth of algae.

Problem Does the supply of phosphate limit the growth of algae?

Materials dropper pipettealgae culture2 test tubes with stopperstest-tube rack50-mL graduated cylinderpond waterglass-marking pencil10% trisodium phosphate solution

Skills Formulating Hypotheses, Predicting

Procedure

Put on your safety goggles, apron, and plastic gloves. Use a dropper pipette toplace 20 drops of algae culture in each of two test tubes.

1.

Use a 50-mL graduated cylinder to add 19 mL of pond water to each test tube.2. Use the glass-marking pencil to label one test tube “control” and the other testtube “phosphate.” Use a dropper pipette to add 2 drops of trisodium phosphate tothe “phosphate” test tube. CAUTION: Trisodium phosphate can injure yourskin. Do not get it on your skin or touch your face after handling it.

3.

Stopper both test tubes and place them in a sunny place. Wash your hands.4. Formulating Hypotheses Record your hypothesis of how phosphate willaffect the growth of the algae if it is a limiting nutrient. Also, record yourprediction of how the two test tubes will appear after 7 days.

5.

Observe the two test tubes each day for the next week. Record your observationseach day, including a labeled sketch of each test tube.

6.

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Chapter 3 The Biosphere

Click on a Key Concept to link to the page where the concept is explained.

3–1 What Is Ecology? Key Concepts

To understand the various relationships within thebiosphere, ecologists ask questions about eventsand organisms that range in complexity from asingle individual to a population, community,ecosystem, or biome, or to the entire biosphere.Scientists conduct modern ecological researchaccording to three basic approaches: observing,experimenting, and modeling. All of theseapproaches rely on the application of scientificmethods to guide ecological inquiry.

Vocabulary

ecologybiospherespeciespopulationcommunityecosystembiome

3–2 Energy Flow Key Concepts

Sunlight is the main energy source for life on Earth.In a few ecosystems, some organisms rely on theenergy stored in inorganic chemical compounds.Energy flows through an ecosystem in one direction,from the sun or inorganic compounds to autotrophs(producers) and then to various heterotrophs(consumers).Only about 10 percent of the energy available withinone trophic level is transferred to organisms at thenext trophic level.

Vocabulary

autotrophproducerphotosynthesischemosynthesisheterotrophconsumerherbivorecarnivoreomnivoredetritivoredecomposerfood chainfood webtrophic levelecological pyramidbiomass

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Chapter 3 The Biosphere

Click the button above to open interactive multiple-choice questions.

Click the button above to open short-answer questions.

Click the button above to open critical-thinking questions.

Click the button above to open a performance-based assessment.

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As you briefly scan the questions, identify those that mayrequire pure guesswork on your part and save them forlast. Then, use your time on those questions to reasonthrough them and eliminate incorrect choices.

Click the button above to open the Standardized Test Prep.

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