Chapter 16 • Ecosystems 339
Opening Activity Ecological Spheres Tell studentsthat scientists have developedsealed glass spheres in which a self-sustaining ecosystem exists.Although there is no input of mate-rials, ask students whether there isan input of anything else into theecosystem. (Yes; there is a constantinput of energy in the form of light.)
IdentifyingMisconceptionsStudents may believe that anecosystem must be an area that isdelineated by specific boundaries—like the walls of an aquarium or theedge of a pond. Point out that thelimits of an ecosystem are definedby the observer. Thus, an ecosystemcould be in a jar of pond water, orit could be the entire pond itself.
Answers1. Autotrophs are able to make
food by using available energyand materials; heterotrophsmust obtain their energy fromthe food produced byautotrophs.
2. In photosynthesis, organismsuse light energy to rearrangethe atoms in carbon dioxideand water to make carbohy-drates. Oxygen is given off tothe environment or used by theorganism itself.
3. In cellular respiration, a carbo-hydrate is combined with oxygen, rearranging its atomsinto carbon dioxide and water.Some of the energy releasedduring this process is availablefor use by the cell.
4. In photosynthesis, an input ofenergy is required, and theenergy is stored in carbohydratemolecules. In cellular respira-tion, this stored energy isreleased for the cell to use.
Answers
1. Agree; as consumers use the plants for food, some of the energy is lost to theenvironment.
2. Agree; some species, called keystonespecies, may be critical links in the foodweb.
Quick Review
Reading Activity
Looking AheadQuick ReviewAnswer the following without referring to
earlier sections of your book.
1. Contrast autotrophs with heterotrophs.
(Chapter 5, Section 1)
2. Summarize the process of photosynthesis.
(Chapter 5, Section 2)
3. Describe the process of cellular respiration.
(Chapter 5, Section 3)
4. Compare the energy flow in photosynthesis
with the energy flow in cellular respiration.
(Chapter 5, Sections 2 and 3)
Did you have difficulty? For help, review the
sections indicated.
Section 1
What Is an Ecosystem?Interactions of Organisms and Their
Environment
Diverse Communities in Ecosystems
Change of Ecosystems over Time
Section 2
Energy Flow in EcosystemsMovement of Energy Through Ecosystems
Loss of Energy in a Food Chain
Section 3
Cycling of Materials in Ecosystems
Biogeochemical Cycles
The Water Cycle
The Carbon Cycle
The Phosphorus and Nitrogen Cycles
www.scilinks.orgNational Science Teachers Association sciLINKS Internet
resources are located throughout this chapter.
Reading ActivityCopy the following statements on a piece of
paper or in your notebook, leaving a few blank
lines after each.
1. In an ecosystem, more energy is stored in
plants than in consumers.
2. The extinction of one species in an ecosystem
can have an impact on all other species.
Before you read the chapter, write down whether
you agree or disagree with each statement. After
you have finished reading the chapter, decide
whether or not you still agree with your first
response.
Materials and energy cycle continuously through the
components of this coral reef. The complex relation-
ship of organisms and their physical environment
makes up an ecological system, or ecosystem.
EcosystemsCHAPTER
16
339
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OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section introducesstudents to the differences betweencommunities and ecosystems.Students will also explore the con-cept of biodiversity, and how onespecies may gradually be replacedby another.
Point to your aquarium (or show apicture of an aquarium with a vari-ety of organisms—different speciesof fish, snails, plants, etc.) and askyour students to list all of theorganisms they see. Tell them thatwhen they finish, they are to makea list of all the factors that affectthe survival of the organisms in theaquarium. (They should include suchthings as water, food, temperaturerange, light, pH, oxygen, and so on.)
Activity Species Count If possible, takethe students on a walk-aroundtour of your school. Point outdifferent species of plants and ani-mals that you observe. Have onestudent keep a count of the num-ber of species identified on thecampus. When finished, mentionthat biologists sampling a tropicalrain forest in Ecuador obtainedsamples suggesting there are asmany as 24,000 different insectspecies alone per acre.
MotivateMotivate
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Section 1
340 Chapter 16 • Ecosystems
GENERAL
CulturalAwarenessCulturalAwareness
Isolated Ecosystem The Yanomami are atribe living in remote rain-forest jungles ofVenezuela and Brazil. The Yanomami inVenezuela have had very little contact withoutsiders and are one of the few culturesremaining in the world in which people arestill an integral part of an intact naturalecosystem. The Yanomami and their land in
Venezuela are protected as an internationalbiosphere reserve. Outsiders must get writtenpermission to visit, but even these few visitshave given the Yanomami a taste of the out-side world. Many observers question howlong the Yanomami hunting and gatheringculture can last.
Section 1 What Is an Ecosystem?
Interactions of Organisms and Their EnvironmentIt is easy to think of the environment as being around but not part
of us—something we always use, sometimes enjoy, and sometimes
damage. But in fact, we are part of the environment along with all
of Earth’s other organisms. All of Earth’s inhabitants are interwoven
in a complex web of relationships, such as the one illustrated in
Figure 1. To understand how the interactions of the parts can affect
a whole system, think about how a computer operates. Removing
one circuit from a computer can change or limit the interactions of
the computer’s many components in ways that influence the com-
puter’s overall operation. In a similar way, removing one species
from our environment can have many consequences, not all of them
easily predictable.
In 1866, the German biologist Ernst Haeckel gave a name to the
study of how organisms fit into their environment. He called this
study ecology, which comes from the Greek words oikos, meaning
“house,” or “place where one lives,” and logos, meaning “study of.”
is the study of the interactions of living organisms with one
another and with their physical environment (soil, water, climate,
and so on). The place where a particular population of a species
lives is its . The many different species that live together in a
habitat are called a . An , or ecological system,
consists of a community and all the physical aspects of its habitat,
such as the soil, water, and weather. The physical aspects of a habi-
tat are called (ay bie AHT ihk) , and the organisms in
a habitat are called .biotic factors
factorsabiotic
ecosystemcommunity
habitat
Ecology
Objectives
● Distinguish an ecosystem
from a community.
● Describe the diversity
of a representative
ecosystem.
● Sequence the process of
succession.
Key Terms
ecology
habitat
community
ecosystem
abiotic factor
biotic factor
biodiversity
pioneer species
succession
primary succession
secondary succession
Figure 1 Organisms
interact within an
ecosystem. Organisms within
an ecosystem continually
change and adjust. This plant
species is dependent on the
bat for its reproduction, and
the bat uses part of the
flower for food.
340
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Group ActivityBiodiversity Before class, find anarea at your school with a goodamount of biodiversity. Organizethe students into groups, and haveeach group create a chart with thefollowing headings: Name,Diagram, Approximate AverageSize, and Approximate Number.Take your students to the area andhave them use their charts to makean inventory of the organisms foundthere. Students may not know thenames of the plants or animals, butthey can make a small diagram ofeach organism, and for the timebeing, make up a fictitious name foreach organism they draw. Havethem save this information to usefor a food web in the next section.
Reading Hint Point out to stu-dents the importance of studyingthe figures in each section. Stronglyencourage them to stop after eachsection and read the captions foreach figure. Prepare questions thatcorrespond to each figure. Forexample, in reference to Figure 1,you might ask students to hypothe-size as to what would happen if theplant species in the photographwere eradicated from the area.
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Chapter 16 • Ecosystems 341
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GENERAL
Chapter Resource File
• Reading Organizers
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Planner CD-ROM
CareerCareerWildlife Biologists are hired by federal, state,and sometimes local government agencies tostudy and manage wildlife. Common game andnongame species, and sometimes rare andendangered species are studied and/or managedby wildlife biologists. Knowledge of eachspecies’ role in the ecosystem and its relation toother species is critical. Starting salary varieswith agency and geographic region.
• Unit 7—Ecosystem Dynamics
This engaging tutorial introducesstudents to Ecosystem Dynamics.
BIOLOGYBIOLOGY
Transparencies
TR Bellringer
TR E25 Ecological Succession at Glacier Bay
Diverse Communities in EcosystemsThe variety of organisms, their genetic differ-
ences, and the communities and ecosystems in
which they occur is termed .
Consider a pine forest in the southeastern
United States, such as the one shown in Figure
2. If you could fence in a square kilometer
(0.4 mi2) of this forest and then collect every
organism, what would you expect to get?
Which of the six kingdoms of organisms
would be represented in your collection?
Ecosystem InhabitantsLarge animals in the forest might include a bear or a white-tailed
deer. The woods also contain smaller mammals—raccoons, foxes,
squirrels, rabbits, and chipmunks. Snakes and toads often remain
hidden among the leaves. Many birds can be found, including
hawks, warblers, and sparrows. If the square kilometer included a
lake, you might find catfish, bass, perch, a variety of turtles, and
perhaps an alligator.
There are pine trees, a variety of smaller trees, and shrubs. Beneath
the trees, grasses and many kinds of flowers grow on the forest floor.
The soil contains an immense number of worms. Hidden under
the bark of trees and beneath the leaves covering the ground are
many different species of insects and spiders, such as those shown
in Figure 3.
Many of the life-forms in the soil and water of a pine forest are
too small to be seen without a microscope. Protists, which include
algae and related microscopic eukaryotes, thrive in water. There
may be billions of bacteria in a handful of soil.
biodiversity
Jumping spider Male stag beetle
The jumping spider is found in sunny, dry parts of the forest. The larvae of the
stag beetle live in and eat decaying wood and bark.
Figure 3 Forest spider and insect
Figure 2 Pine forest.
Pine forests like this one are
common in the southeastern
United States.
www.scilinks.org
Topic: Biodiversity
Keyword: HX4020
341
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Teaching Tip Detritivores Bacteria and fungibelong to a group of organismsknown as detritivores, which live ondetritus, the dead remains of plantsand animals. Ask students to thinkof other organisms that would bedetritivores. (Maggots, grubs, andearthworms would be examples.)
Teach, continuedTeach, continued
Introduced Species Introducing species tonew areas can wreak havoc on an ecosystem.In the 1870s Lord George Bennet founded thesmall coastal town of Bandon, Oregon. Bennetis also the one believed by many to haveimported a plant called gorse (Ulex europaeus)from his native Ireland. Gorse spreads out rap-idly, leaving a dead, dry center. Its nasty thornsmake it difficult to remove, and its naturallyhigh oil content makes it very flammable and
causes it to reach high temperatures when itburns. Having no natural enemies in Oregon,gorse spread quickly and could not be con-trolled. On Sept. 26, 1936, a spark from anearby fire ignited a gorse thicket whicheventually spread to burn 287,000 acres,destroying all but 16 of Bandon’s nearly 500buildings and killing 14 people. In 1994 thegorse spider mite was released near Bandon tohelp control this noxious weed.
342 Chapter 16 • Ecosystems
GENERAL
Evaluating Biodiversity
Skills AcquiredObserving, drawingconclusions
Teacher’s Notes
Have each student use an areaof equal dimensions, at least50 3 50 m, to make the taskmore manageable and to allowcomparisons between differentecosystems. Encourage studentsto take their time; they willobserve much more if they do.
Answers to Analysis1. Answers will vary.
2. Answers will vary. Example:3 robins/29 total organisms 50.103 5 10%
3. Answers will vary.
4. Answers will vary. In general,the abiotic factors in anecosystem provide organisms(biotic factors) with a physicalplace to live, energy, nutrients,and water. The organisms alterand recycle some of theseabiotic factors, changing thelandscape in the process.
You might find many kinds of fungi growing on fallen trees and
spreading as fine threads through the decaying material on the forest
floor, as illustrated in Figure 4. Other fungi are found on the surface
of trees or rocks as lichens. Lichens are associations between fungi
and algae or cyanobacteria.
If you were to remove every organism from your square kilometer,
the nonliving surroundings that remain make up the abiotic factor.
This would include the minerals, organic compounds, water, wind
that blows over the Earth, rain, and sunlight.
Ecosystem Boundaries The physical boundaries of an ecosystem are not always obvious,
and they depend on how the ecosystem is being studied. For exam-
ple, a scientist might consider a single rotting log on the forest floor
to be an ecosystem if he or she is interested only in the fungi and
insects living in the log. Often individual fields, forests, or lakes are
studied as isolated ecosystems. Of course, no location is ever totally
isolated. Even oceanic islands get occasional migrant visitors, such
as birds blown off course.
Mushrooms are often found on moist
forest floors.
Shelf fungi grow on and digest trees.
These fungi digest plants and
other materials they find in the
forest.
Figure 4 Forest fungi
Evaluating BiodiversityBy making simple observations, you can draw
some conclusions about biodiversity in an ecosystem.
Materials
note pad, pencil
Procedure
1. CAUTION: Do
not approach
or touch any wild animals.
Do not disturb plants.
Prepare a list of biotic and
abiotic factors that you
observe around your home
or in a nearby park.
Analysis
1. Identify the habitat and
community that you observed.
2. Calculate the number of dif-
ferent species as a percentage
of the total number of organ-
isms that you saw.
3. Rank the importance of
biotic factors within the
ecosystem you observed.
4. Infer what the relationships
are between biotic factors
and abiotic factors in the
observed ecosystem.
342
Copyright © by Holt, Rinehart and Winston. All rights reserved.
water. When a gopher emerged, the moundthey made would catch seeds blowing acrossthe moon-like landscape, helping plants to getstarted. In another surprise to scientists, thegophers helped to save amphibians, whichused the tunnels as cool underground areas inwhich to avoid the hot, dry landscape.
DemonstrationBring to class a rock covered withlichens or mosses. Ask students whythese organisms are known as “pio-neer species.” (Like pioneer settlers,they are the first to inhabit a newarea.) Point out that lichen canabsorb nutrients from the bare rock.
Teaching TipSuccession Have each studentdraw an illustrated timeline repre-senting the succession that occursafter a forest fire has burned all ofthe vegetation in an area. Startingat time zero, the land should bebarren, followed by the appearanceof grasses and weeds, then smallbushes, and finally trees. Visual
Using the FigureHave students examine the topphoto in Figure 5. Ask them tothink of other events that mightoccur that would lead to primarysuccession. (Landslides and volcan-ism would be examples.) Tell stu-dents that primary succession canbe a very slow process. Scientistsestimate that the primary succes-sion from sand dunes to the beech-maple forest along the shores ofLake Michigan took about 1,000years. In contrast, secondary suc-cession may take less than 100years. Ask students why the hem-lock and spruce trees don’t comebefore the grasses and shrubs. (Thegrasses and shrubs often provide amicrohabitat that makes it possiblefor the seeds of the trees to survive.)
GENERAL
LS
GENERAL
Chapter 16 • Ecosystems 343
did you know?
Mount St. Helens After the eruption ofMount St. Helens on May 18, 1980, succes-sion was aided by an unlikely source—pocketgophers. Pocket gophers that survived theblast dug miles of tunnels under the barrenpumice fields. The digging helped mix the soil,which improved its quality and ability to hold
Change of Ecosystems over TimeWhen a volcano forms a new island, a glacier recedes and exposes
bare rock, or a fire burns all of the vegetation in an area, a new
habitat is created. This change sets off a process of colonization
and ecosystem development. The first organisms to live in a new
habitat where soil is present tend to be small, fast-growing plants,
called . They may make the ground more hos-
pitable for other species. Later waves of plant immigrants may
then outcompete and replace the pioneer species.
SuccessionA somewhat regular progression of species replacement is
called . Succession that occurs where life has
not existed before is called . Succession
that occurs in areas where there has been previous growth,
such as in abandoned fields or forest clearings, is called
. It was once thought that the stages of
succession were predictable and that succession always led to
the same final community of organisms within any particular
ecosystem. Ecologists now recognize that initial conditions
and chance play roles in the process of succession. For exam-
ple, if two species are in competition, a sudden change in the
climate may favor the success of one species over the other.
For this reason, no two successions are alike.
Glacier Bay: an Example of SuccessionA good example of primary succession is a receding glacier
because land is continually being exposed as the face of the
glacier moves back. The glacier that composes much of the
head of Glacier Bay, Alaska, has receded some 100 km
(62 mi) over the last 200 years. Figure 5 shows the kinds of
changes that have taken place as time passed.
The most recently exposed areas are piles of rock and
gravel that lack the usable nitrogen essential to plant and ani-
mal life. The seeds and spores of pioneer species are carried
in by the wind. These include lichens, mosses, fireweed, wil-
lows, cottonwood, and Dryas, a sturdy plant with clumps
about 30 cm (1 ft) across. At first all of these plants grow
close to the ground, severely stunted by mineral deficiency,
but Dryas eventually crowds out the other plants.
After about 10 years, alder seeds blown in from distant
sites take root. Alder roots have nitrogen-fixing nodules, so
they are able to grow more rapidly than Dryas. Dead leaves
and fallen branches from the alder trees add more usable
nitrogen to the soil. The added nitrogen allows willows and
cottonwoods to invade and grow with vigor. After about 30
years, dense thickets of alder, willow, and cottonwood shade
and eventually kill the Dryas.
secondary succession
primary succession
succession
pioneer species
Recently exposed land has few nutrients.
Alders, grasses, and shrubs later take over
from pioneer plants.
As the amount of soil increases, spruce and
hemlock trees become plentiful.
A receding glacier makes primary
succession possible.
Figure 5 Glacier Bay
343
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ReteachingShow students a picture of a forestecosystem. Have them describe theevents that would take place aftera fire.
Quiz1. What is the difference between
communities and ecosystems?(An ecosystem is a community andits abiotic factors.)
2.How are the boundaries of anecosystem set? (in whatever waymakes it easier to study)
GENERAL
CloseClose
Answers to Section Review
1. the abiotic environment
2. Because the land is kept in a constant state ofdisturbance, secondary succession in gardensand farms does not usually get beyond the firststage of fast-growing weeds and grasses.
3. Primary succession occurs on land where therehas not been any previous plant growth, suchas recently exposed land that has few nutrients.Secondary succession occurs in areas wherethere has been previous plant growth, such asin abandoned fields or forest clearings.
4. Answers may vary, but students should citefactors such as climate, geology, and humanintervention.
5. A. Correct. B. Incorrect. They do requireminerals. C. Incorrect. Alders do have roots.D. Incorrect. Alders are not shade tolerant.
344 Chapter 16 • Ecosystems
ModelingSuccession
Skills AcquiredObserving, inferring
Teacher’s NotesMake sure students do notscrew the lid down on the jarstoo tightly because the growingculture will suffocate, or the jarmay explode from anaerobi-cally produced gas.
Answers to Analysis1. The pH dropped as the envi-
ronment became more acidic.
2. By-products from the microor-ganisms change the pH. Thennew organisms that are betteradapted to the changed pHbegin to thrive.
3. Like the Glacier Bay model,organisms colonize and slowlychange a new environmentsuch that it becomes moresuitable for other organisms.
Teach, continuedTeach, continued
About 80 years after the glacier first exposes the land, Sitka
spruce invades the thickets. Spruce trees use the nitrogen released
by the alders and eventually form a dense forest. The spruce blocks
the sunlight from the alders, and the alders then die, just as the
Dryas did before them. After the spruce forest is established, hem-
lock trees begin to grow. Hemlocks are very shade tolerant and have
a root system that competes well against spruce for soil nitrogen.
Hemlock trees soon become dominant in the forest. This commu-
nity of spruce and hemlock proves to be a very stable ecosystem
from the perspective of human time scales, but it is not permanent.
As local climates change, this forest ecosystem may change too.
Modeling SuccessionYou can create a small ecosystem and measure
how organisms modify their environment.
Materials
1 qt glass jar with a lid, one-half quart of pasteurized
milk, pH strips
Procedure
1. Prepare a table like the one
below.
2. Half fill a quart jar with
pasteurized milk, and cover
the jar loosely with a lid.
Measure and record the
pH. Place the jar in a 37°C
incubator.
3. Check and record the pH of
the milk with pH strips every
day for seven days. As milk
spoils, its pH changes.
Different populations of
microorganisms become
established, alter substances
in the milk, and then die off
when conditions no longer
favor their survival.
4. Record any visible changes
in the milk each day.
Analysis
1. Identify what happened to
the pH of the milk as time
passed.
2. Infer what the change in
pH means about the popu-
lations of microorganisms in
the milk.
3. Critical Thinking
Evaluating Results How
does this model confirm the
model of succession in
Glacier Bay?
DATA TABLE
Day pH Appearance
1
2
3
Identify what components of an ecosystem arenot part of a community.
Relate how gardening or agriculture affectssuccession.
Differentiate primary succession fromsecondary succession.
Critical Thinking Applying Information
Why do some ecosystems remain stable forcenturies, while others undergo succession?
In the succession thatoccurs as a glacier recedes, alders can growrelatively rapidly because alders have
A nitrogen-fixing nodules. C no roots.
B no need for minerals. D shade tolerance.
Standardized Test PrepStandardized Test Prep
Section 1 Review
344
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Section 2
Overview
Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section discusses howproducers and consumers facilitatethe flow of energy through ecosys-tems in the form of food webs andfood chains. Students will then dis-cover that a depletion in theamount of available energy limitsthe number of steps that can occurin a food chain.
Tell students to think about theirlocal area and make a diagram of afood chain that would be typicalfor your area. Ask them to try toput 6 organisms into the foodchain. (It is very difficult to do—askstudents why this is so, and lead intoa discussion of trophic levels andenergy loss.)
Demonstration
List the following organisms thatcan be found in an open field: robin,hawk, snake, frog, grasshopper,mouse, and rabbit. Have studentsdraw arrows to show what eatswhat in this field ecosystem.Students should see the complexityof even this simple food web inwhich each predator can take morethan one type of prey and each typeof prey could be exploited by sev-eral different species of predators.
GENERAL
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Chapter 16 • Ecosystems 345
• Directed Reading
• Active Reading GENERAL
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Transparencies
TR Bellringer
TR E4 Trophic Levels
TR E5 Food Chain in an AntarcticEcosystem
TR E6 Food Web in an AntarcticEcosystem
Movement of Energy Through EcosystemsEverything that organisms do in ecosystems—running, breathing,
burrowing, growing—requires energy. The flow of energy is the
most important factor that controls what kinds of organisms live in
an ecosystem and how many organisms the ecosystem can support.
In this section you will learn where organisms get their energy.
Primary Energy Source Most life on Earth depends on photosynthetic organisms, which cap-
ture some of the sun’s light energy and store it as chemical energy in
organic molecules. These organic compounds are what we call food.
The rate at which organic material is produced by photosynthetic
organisms in an ecosystem is called . Primary
productivity determines the amount of energy available in an ecosys-
tem. Most organisms in an ecosystem can be thought of as chemical
machines driven by the energy captured in photosynthesis.
Organisms that first capture energy, the , include plants,
some kinds of bacteria, and algae. Producers make energy-storing
molecules. All other organisms in an ecosystem are consumers.
are those organisms that consume plants or other organ-
isms to obtain the energy necessary to build their molecules.
Trophic LevelsEcologists study how energy moves through an ecosystem by
assigning organisms in that ecosystem to a specific level, called a
(TROHF ihk) , in a graphic organizer based on the
organism’s source of energy. Energy moves from one trophic level to
another, as illustrated in Figure 6.
leveltrophic
Consumers
producers
primary productivity
Energy Flow in Ecosystems
Section 2
Objectives
● Distinguish between
producers and
consumers.
● Compare food webs with
food chains.
● Describe why food chains
are rarely longer than three
or four links.
Key Terms
primary productivity
producer
consumer
trophic level
food chain
herbivore
carnivore
omnivore
detritivore
decomposer
food web
energy pyramid
biomass
The sun is the ultimate source of energy for producers and all consumers.
Figure 6 Trophic levels
ProducerSun Consumer Consumer
345
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Interactive Reading AssignChapter 16 of the Holt BiologyGuided Audio CD Program to helpstudents achieve greater success inreading the chapter.
Teaching TipTrophic Levels Ask a volunteerfrom the class to describe his or herdinner last night. Then have stu-dents describe the trophic level ofeach different food item in themeal. What was the trophic level ofthe student as he or she ate eachitem? (Answers will vary.) Verbal
Using the FigureAsk students to look at the foodchain in Figure 7. Ask students ifthis picture shows a lot of diversity.(no) Ask them what would happento this food chain if leopard sealsate only cod, killer whales ate onlyleopard seals, and a disease wipedout all of the cod. (Leopard sealsand killer whales would starve.)
LS
GENERAL
SKILL
BUILDER
READINGREADING
TeachTeach
346 Chapter 16 • Ecosystems
Answer
These bacteria are chemosynthetic(as opposed to photosynthetic)producers. They are at the bot-tom of their food chain.
Real Life
Integrating Physics and Chemistry
Reiterate that digestion involves physical and chemicalchanges. Whereas physical processes of digestionchange large pieces of food into smaller ones primarilyby means of chewing and muscle movements of thestomach and the intestines, chemical digestion takesplace when various enzymes are added to the ingestedfood. These enzymes chemically break down foodparticles into molecules that are small enough to beabsorbed and used by an organism’s cells.
First Level The path of energy through the trophic levels of an
ecosystem is called a . An example is shown in Figure 7.
The lowest trophic level of any ecosystem is occupied by the pro-
ducers, such as plants, algae, and bacteria. Producers use the energy
of the sun to build energy-rich carbohydrates. Many producers also
absorb nitrogen gas and other key substances from the environment
and incorporate them into their biological molecules.
Second Level At the second trophic level are (HUHR beh
vohrz), animals that eat plants or other primary producers. They are
the primary consumers. Cows and horses are herbivores, as are cater-
pillars and some ducks. A herbivore must be able to break down a
plant’s molecules into usable compounds. However, the ability to
digest cellulose is a chemical feat that only a few organisms have
evolved. As you will recall, cellulose is a complex carbohydrate found
in plants. Most herbivores rely on microorganisms, such as bacteria
and protists, in their gut to help digest cellulose. Humans cannot
digest cellulose because we lack these particular microorganisms.
Third Level At the third trophic level are secondary consumers, ani-
mals that eat other animals. These animals are called .
Tigers, wolves, and snakes are carnivores. Some animals, such as
bears, are both herbivores and carnivores; they are called
(AHM nih vohrz). They use the simple sugars and starches stored in
plants as food, but they cannot digest cellulose.
In every ecosystem there is a special class of consumers called detri-
tivores, which include worms and fungal and bacterial decomposers.
(deh TRIH tih vohrz) are organisms that obtain their
energy from the organic wastes and dead bodies that are produced at
Detritivores
omnivores
carnivores
herbivores
food chainReal Life
Not all producers are
photosynthetic.
At the bottom of oceans
near volcanic
vents live
bacteria that
harvest
energy from
the reduced
sulfur compounds ejected
by these volcanic vents.
Applying Information
Where in their food
chains do these
bacteria lie?
Algae
Krill
Cod
Leopard seal
This food chain shows one path of energy flow in an Antarctic ecosystem.
Figure 7 Aquatic food chain
Killer whale
346
MISCONCEPTION
ALERT
Food Chains vs. Food Webs Emphasizethat food chains, while being useful toolsfor showing the flow of energy through anecosystem, can be misleading to studentsbecause they imply that each organism eatsONLY the organism below it in the foodchain. We know, of course, that mostorganisms eat a wide variety of otherorganisms, and for this reason the term“food web” gives a more accurate pictureof what actually happens in an ecosystem.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching Tip Understanding the Flow ofEnergy Have students draw aGraphic Organizer that summarizesthe flow of energy from producersto herbivores, omnivores,carnivores, and detritivores. Acompleted graphic organizer isshow at the bottom of this page.
Group ActivityFood Webs & BiodiversityOrganize students into groups of 4.Obtain sheets of butcher paper(each about 2–3 feet on a side).Have one student in each groupbegin by writing the name of anorganism anywhere on the sheet inlarge letters. After the name theyshould write one of these letters:P (producer), C (carnivore), H (herbivore), O (omnivore), andD (detritivore). Moving clockwise,each student writes the name ofanother organism randomly on thesheet. Each student draws an arrowfrom this organism to anything thateats it, and an arrow to this organ-ism from organisms it would eat.Continue until the food web getsvery messy. Stop the activity andhave each group hold up theirpaper and have the class “vote” onwhich food web shows the greatestbiodiversity. Discuss what wouldhappen to the “winning” food webif just one organism becameextinct. (In most cases there wouldbe no effect if there were a lot of bio-diversity, but if the extinct organismwas the only producer, it could havea profound effect.) Co-op Learning
GENERAL
Chapter 16 • Ecosystems 347
Algae
Small animals
and protists
Krill
Cod Squid
Leopard
seal
Killer whale
Adelie
penguin
Crabeater seal
Elephant seal
all trophic levels. Bacteria and fungi are known as
because they cause decay. Decomposition of bodies and wastes releases
nutrients back into the environment to be recycled by other organisms.
Many ecosystems contain a fourth trophic level composed of
those carnivores that consume other carnivores. They are called ter-
tiary consumers, or top carnivores. A hawk that eats a snake is a
tertiary consumer. Very rarely do ecosystems contain more than
four trophic levels.
In most ecosystems, energy does not follow simple straight paths
because individual animals often feed at several trophic levels. This
creates a complicated, interconnected group of food chains called a
, as illustrated in Figure 8. food web
decomposers
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Topic: Food Chains and Webs
Keyword: HX4085
This food web shows a more complete picture of the feeding relationships in an
Antarctic ecosystem.
Figure 8 Aquatic food web
347
Use this graphic organizer with
Teaching Tip on this page.
Graphic Organizer
Detritivores: consume producers,
herbivores, carnivores, and omnivores
Producers: make
energy-storing molecules
Herbivores:
consume producers
Carnivores:
consume herbivores
Omnivores: consume
producers and herbivores
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching TipPhysics Remind students that thefirst law of thermodynamics statesthat energy cannot be created ordestroyed but only changed in form.Have students give examples ofenergy changes from one form intoanother. (Examples: in a light bulb,electrical energy is changed to lightenergy and heat; batteries changechemical energy into electrical energy)The second law states that energychange between forms is never 100percent efficient. Ask students tothink of an example that shows theinefficiency of energy conversions.(In an automobile engine, gasoline—chemical energy—is changed tokinetic energy to turn the wheels;however, much of the energy is con-verted to heat, which is unavailable topower the automobile.) Logical
Interpreting Visuals Have stu-dents examine the energy pyramidshown in Figure 9. Ask studentshow many trophic levels there arein the diagram. (4) Have them notethat the top trophic level is verysmall. Ask them how the size of theupper level relates to the fact thatthere are a small number of trophiclevels. (There is not enough energy tosupport another level of consumers.)
BUILDERSKILL
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GENERAL
Teach, continuedTeach, continued
348 Chapter 16 • Ecosystems
Transparencies
TR E8 Energy Transfer ThroughTrophic Levels
TR E11 Energy Efficiency in Food Consumption
MISCONCEPTION
ALERT
Lost Energy It is quite common for teachersand students to refer to energy being “lost.”Remind students that the first law of thermo-dynamics says energy cannot be “lost”—itcan only be converted from one form intoanother. What people mean when they say
“lost” is that the energy is made unavailable—usually in the form of heat. For example,when an automobile engine heats up, the heatenergizes nearby air molecules as it leaves theengine, but this heat cannot realistically beused to move the automobile.
www.scilinks.org
Topic: Energy Pyramids
Keyword: HX4069
Producers
Herbivores
Carnivore
Top carnivore
Loss of Energy in a Food ChainA deer browsing on leaves is acquiring energy. Potential energy is
stored in the chemical bonds within the molecules of the leaves.
Some of this energy is transformed to other forms of potential
energy, such as fat. Some of it aids the deer in running and breath-
ing, and in fueling cellular processes. But much of the energy is
dispersed into the environment as heat.
Energy TransferDuring every transfer of energy within an ecosystem, energy is lost as
heat. Although heat can be used to do work (as in a steam engine), it
is generally not a useful source of energy in biological systems. Thus,
the amount of useful energy available to do work decreases as energy
passes through an ecosystem. The loss of useful energy limits the
number of trophic levels an ecosystem can support. When a plant
harvests energy from sunlight, photosynthesis captures only about 1
percent of the energy available to the leaves. When a herbivore uses
plant molecules to make its own molecules, only about 10 percent of
the energy in the plant ends up in the herbivore’s molecules. And
when a carnivore eats the herbivore, about 90 percent of the energy
is lost in making carnivore molecules. At each trophic level, the
energy stored by the organisms in a level is about one-tenth of that
stored by the organisms in the level below.
The Pyramid of EnergyEcologists often illustrate the flow of energy through ecosystems
with an energy pyramid. An is a diagram in which
each trophic level is represented by a block, and the blocks are
stacked on top of one another, with the lowest trophic level on the
bottom. The width of each block is determined by the amount of
energy stored in the organisms at that trophic level. Because the
energy stored by the organisms at each trophic level is about one-
tenth the energy stored by the organisms in the level below, the
diagram takes the shape of a pyramid, as shown in Figure 9.
energy pyramid
The word ecosystem is
from the Greek words
oikos, meaning “house,”
and systematos, meaning
“to place together.”
Knowing this information
makes it easier to
remember that an
ecosystem includes a
community of living things
as well as all physical
aspects of its environment.
In this simple ecosystem, each
trophic level contains about 90
percent less energy than the
level below it.
Figure 9 Trophic levels of
a terrestrial ecosystem
348
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Answers to Section Review
1. Producers use energy (usually from the sun) toassemble food molecules, hence “producingfood.” Consumers must take in (or consume)these food molecules to obtain their energy.
2. As energy moves through the food chain, about90 percent is “lost” at each level. So, 1,000kilocalories in grass eaten by a rabbit wouldresult in only about 100 available to the foxthat eats the rabbit. The eagle that eats the foxwould only have 10 kilocalories of the original1,000 kilocalories available.
3. Answers will vary. Students should be able to explain the interactions between all theorganisms.
4. Because so much energy is “lost” at eachtrophic level, it is difficult to exceed four links, or trophic levels.
5. Plants are the producers that make food.Without them, animals would starve.
6. A. Incorrect. Algae is the producer.B. Incorrect. Cod is not a producer.C. Incorrect. A leopard seal is not a producer.D. Correct. Algae is the producer, and mustcome first in the food chain.
Activity Energy in Trophic Levels Tell stu-dents that if an average of 1,500kilocalories of light energy per dayfalls on a square meter of land sur-face covered by plants, only about15–30 kilocalories become incorpo-rated into chemical compoundsthrough photosynthesis. Howmuch of this energy could end upin a person who eats these plants?(1.5–3.0 kilocalories) How much ofthis energy could end up in a per-son who eats a steak from a steerthat ate the plants? (0.15–0.30kilocalories) Logical
ReteachingHave students construct a food weband energy pyramid for the school-yard. Ask students to identifyproducers, herbivores, omnivores,carnivores, and detritivores. Whatspecies would they expect to find ifthe area had been a natural park.
Quiz1. What do all consumers rely on
for their food? (producers)
2. Give an example of consumersoutnumbering the producers thatthey are feeding upon. (One treemight have thousands of insectsfeeding on it.)
AlternativeAssessmentHave students draw a food chain, afood web, and an energy pyramidfor any ecosystem. They mustchoose enough organisms for severaltrophic levels and feeding pathways.
GENERAL
CloseClose
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Chapter 16 • Ecosystems 349
GENERAL
Limitations of Trophic LevelsMost terrestrial ecosystems involve only
three or, on rare instances, four levels. Too
much energy is lost at each level to allow
more levels. For example, a large human
population could not survive by eating
lions captured on the Serengeti Plain of
Africa because there are too few lions to
make this possible. The amount of grass in
that ecosystem cannot support enough
zebras to maintain a large enough popula-
tion of lions to feed lion-eating humans. In
other words, the number of trophic levels
that can be maintained in a community is
limited by the dispersal of potential energy.
Humans are omnivores, and unlike lions,
we can choose to eat either meat or plants.
As illustrated in Figure 10, about 10 kg
(22 lb) of grain are needed to build about
1 kg (2.2 lb) of human tissue if the grain is
directly ingested by a human. If a cow eats
the grain and a human eats the cow, then
about 100 kg (220 lb) of grain are needed to
build about 1 kg (2.2 lb) of human tissue.
Also, the number of individuals in a
trophic level may not be an accurate indica-
tor of the amount of energy in that level.
Some organisms are much bigger than oth-
ers and therefore use more energy. Because
of this, the number of organisms often does not form a pyramid when
one compares different trophic levels. For instance, caterpillars and
other insect herbivores greatly outnumber the trees they feed on. To
better determine the amount of energy present in trophic levels, ecol-
ogists measure biomass. is the dry weight of tissue and other
organic matter found in a specific ecosystem. Each higher level on the
pyramid contains only 10 percent of the biomass found in the trophic
level below it.
Biomass
It takes 10 times
more grain
to feed one cow
to make enough beef
to provide one
person with the same
amount of energy.
It takes a certain
amount of grain
to produce
enough bread
to provide one
person with a certain
amount of energy.
Adding a trophic level to a food chain increases the
energy demand of consumers by a factor of about 10.
Figure 10 Energy efficiency in food consumption
Section 2 Review
Explain how producers differ from consumers.
Analyze the flow of energy through a food chainthat contains four tropic levels, one of which is acarnivore.
Construct a food web, and explain the inter-actions of the organisms that compose it.
List the reasons why food chains do not tend toexceed four links.
Critical Thinking Justifying an Argument
Explain why scientists believe that most animalswould become extinct if all plants died.
Which series shows a cor-rect path of energy flow in a marine food chain?
A krill → cod → algae
B cod → leopard seal → krill
C leopard seal → algae → krill
D algae → krill → cod
Standardized Test PrepStandardized Test Prep
349
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Overview
Before beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section explains howimportant materials necessary forsurvival, such as water, carbon,phosphorus, and nitrogen, rotatethrough natural systems, constantlyre-supplying organisms. Studentswill also learn that bacteria play animportant role in the recycling ofmany elements.
Have students make a list of any-thing they have used in the pastweek that had previously beenrecycled or is made of recycledmaterials. After they have madetheir lists, have students volunteeritems and discuss what the item isrecycled from, if known, and thepluses and minuses (if any) of recy-cling each item.
Discussion
Make the following statement toyour class: “Someone once saidthat if a person dumped a glass ofwater on the ground, one year later,no matter where they were onEarth, any glass of water they pourwould contain at least one mole-cule of water from the originalglass.” Ask students if they thinkthis is true, and if so, how couldthis occur? (Probably not, but itmakes for a great discussion aboutthe water cycle!)
GENERAL
MotivateMotivate
Bellringer
FocusFocus
Section 3
350 Chapter 16 • Ecosystems
• Directed Reading
• Active Reading GENERAL
Chapter Resource File
• Reading Organizers
• Reading Strategies
• Supplemental Reading Guide Silent Spring
Planner CD-ROM
Transparencies
TR Bellringer
TR Graphic Organizer
TR Concept Map
TR E12 Water Cycle
TR E13 Carbon Cycle
TR E14 Nitrogen Cycle
Section 3 Cycling of Materials in Ecosystems
Biogeochemical CyclesHumans throw away tons of garbage every year as unwanted,
unneeded, and unusable. Nature, however, does not throw anything
away. Most energy flows through the Earth’s ecosystems from the sun
to producers to consumers. The physical parts of the ecosystems,
however, cycle constantly. Carbon atoms, for example, are passed
from one organism to another in a great circle of use. Producers are
eaten by herbivores, herbivores are eaten by carnivores, and carni-
vores are eaten by top carnivores. Eventually the top carnivores die
and decay; their carbon atoms then become part of the soil to feed the
producers in a long and complex cycle that reuses this important ele-
ment. Carbon is not the only element that is constantly recycled in
this way. Other recycled elements include many of the inorganic (non-
carbon) substances that make up the soil, water, and air, such as
nitrogen, sulfur, calcium, and phosphorus.
All materials that cycle through living organisms are important in
maintaining the health of ecosystems, but four substances are partic-
ularly important: water, carbon, nitrogen, and phosphorus. All
organisms require carbon, hydrogen, oxygen, nitrogen, phosphorus,
and sulfur in relatively large quantities. They require other elements,
such as magnesium, sodium, calcium, and iron, in smaller amounts.
Some elements, such as cobalt and man-
ganese, are required in trace amounts.
The paths of water, carbon, nitrogen, and
phosphorus pass from the nonliving environ-
ment to living organisms, such as the trees in
Figure 11, and then back to the nonliving
environment. These paths form closed cir-
cles, or cycles, called biogeochemical (bie
oh jee oh KEHM ih kuhl) cycles. In each
, a pathway forms when
a substance enters living organisms such as
trees from the atmosphere, water, or soil;
stays for a time in the living organism; then
returns to the nonliving environment.
Ecologists refer to such substances as cycling
within an ecosystem between a living reser-
voir (an organism that lives in the ecosystem)
and a nonliving reservoir. In almost all bio-
geochemical cycles, there is much less of the
substance in the living reservoir than in the
nonliving reservoir.
biogeochemical cycle
Objectives
● Summarize the role of
plants in the water cycle.
● Analyze the flow of energy
through the carbon cycle.
● Identify the role of bacteria in
the nitrogen cycle.
Key Terms
biogeochemical cycle
ground water
transpiration
nitrogen fixation
Figure 11 Trees and the carbon cycle. Approximately
500 million tons of carbon were taken up as a result of
forest regrowth in the Northern Hemisphere between
1980 and 1989.
350
Copyright © by Holt, Rinehart and Winston. All rights reserved.
water molecules and bonding with them.When they reach 0º C they have formed a uni-form latticework of water molecules called ice.Because ice is less dense than the warmer wateraround it, it floats. This property is critical forliving organisms, because the floating ice insu-lates the water beneath it. This prevents thewater under the ice from freezing solid, killingthe organisms in it.
Paired Reading Pair each studentwith a partner. You may want topair ELL students with nativeEnglish speakers. Have each studentread about the water cycle silentlywhile making a question mark on asticky note next to the passages thatthey find confusing. After they fin-ish reading, ask one student tosummarize and the second to addanything omitted. Both readersshould then help each other withany passages that either (or both)did not understand. Have themcreate a list of questions to ask theclass. Students should repeat thisprocess for the carbon and nitrogencycles. Interpersonal
Using the FigureHave each student look atFigure 12 and notice the twoarrows labeled “evaporation” andthe one arrow labeled “transpira-tion.” Ask them what is needed forevaporation or transpiration tooccur. (an input of energy) Next askstudents if this input of energy thatcauses evaporation and transpira-tion can be harvested by humans,and if so, how? (As the clouds thathold the evaporated and transpiredwater move across the land, precipi-tation may occur, and the waterrunoff may eventually enter a river. Ifthe river has a hydroelectric dam onit, the water will run through the tur-bines, spinning them and convertingthe energy of the water into electricalenergy, to be used by man.)
GENERAL
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SKILL
BUILDER
READINGREADING
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Chapter 16 • Ecosystems 351
Changes in State of Water Water is aunique liquid because, unlike other liquids, it isnot at its densest point when it freezes. Picturea pond in early winter. As the water cools inthe pond, its molecules pack in tighter andtighter until the water reaches 4º C, at whichpoint it is at its densest. As the water continuesto cool, the molecules now begin moving apartfrom each other as they swing outward—like adoor on a hinge—being attracted to other
CHEMISTRYCHEMISTRYCONNECTIONCONNECTION
Transpiration
Precipitation
Water vapor(clouds)
EvaporationEvaporation
Runoff
LakeOcean
Groundwater Percolation
into soil
The Water Cycle Of all the nonliving components of an ecosystem, water has the great-
est influence on the ecosystem’s inhabitants. In the nonliving portion
of the water cycle, water vapor in the atmosphere condenses and falls
to the Earth’s surface as rain or snow. Some of this water seeps into
the soil and becomes part of the , which is water
retained beneath the surface of the Earth. Most of the remaining
water that falls to the Earth does not remain at the surface. Instead,
heated by the sun, it reenters the atmosphere by evaporation. The
path of water within an ecosystem is shown in Figure 12.
In the living portion of the water cycle, much water is taken up by
the roots of plants. After passing through a plant, the water moves
into the atmosphere by evaporating from the leaves, a process called
. Transpiration is also a sun-driven process. The sun
heats the Earth’s atmosphere, creating wind currents that draw
moisture from the tiny openings in the leaves of plants.
In aquatic ecosystems (lakes, rivers, and oceans), the nonliving
portion of the water cycle is the most important. In terrestrial ecosys-
tems, the nonliving and living parts of the water cycle both play
important roles. In thickly vegetated ecosystems, such as tropical
rain forests, more than 90 percent of the moisture in the ecosystem
passes through plants and is transpired from their leaves. In a very
real sense, plants in rain forests create their own rain. Moisture trav-
els from plants to the atmosphere and falls back to the Earth as rain.
transpiration
ground water
www.scilinks.org
Topic: Water Cycle
Keyword: HX4188
This diagram shows the major steps in the water cycle.
Figure 12 Water cycle
351
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Teaching Tip Atmospheric Carbon DioxideHave each student make a list ofactivities that contribute to risinglevels of carbon dioxide. (Burninggasoline in a car, propane in a stove,charcoal in a barbecue, etc.) Askthem how electrical power is gener-ated in your area. If fossil fuels areburned, then their use of electricityalso contributes (indirectly) to car-bon dioxide levels. Have studentsidentify ways to reduce the amountof carbon dioxide they contribute.Afterwards, encourage interestedstudents to use the InternetConnect box to learn more aboutthe carbon cycle. Intrapersonal
Using the FigureHave students observe theprocesses of the carbon cycle asdepicted in Figure 13. Point outthat an increase in “activity” in onepart of the cycle will affect otherparts of the cycle. Ask studentswhich part of the carbon cycle haschanged the most drastically overthe last 200 years. (the amount ofcombustion due to the IndustrialRevolution) VisualLS
LS
Teach, continuedTeach, continued
“greenhouse effect.” Many scientists believethat a buildup of carbon dioxide in the atmos-phere may act like the glass in a car, absorbingthe heat, causing the atmosphere to slowlyheat up. This could have disastrous effects. Ifthe greenhouse effect causes an increase in themelting of the polar ice caps, coastal areascould experience serious flooding.
352 Chapter 16 • Ecosystems
GENERAL
did you know?
Greenhouse Effect As light energy enters acar windshield in the heat of summer, some ofthe energy is lost, and the high energy, short-wavelength light is changed to lower energy,long-wavelength heat. The longer wavelengthcannot escape through the glass, and theinside of the car heats up. This process alsooccurs in greenhouses and is known as the
www.scilinks.org
Topic: Carbon Cycle
Keyword: HX4031
The Carbon Cycle Carbon also cycles between the nonliving environment and living
organisms. You can follow the carbon cycle in Figure 13. Carbon
dioxide in the air or dissolved in water is used by photosynthesizing
plants, algae, and bacteria as a raw material to build organic mol-
ecules. Carbon atoms may return to the pool of carbon dioxide in
the air and water in three ways.
1. Respiration. Nearly all living organisms, including plants,
engage in cellular respiration. They use oxygen to oxidize organic
molecules during cellular respiration, and carbon dioxide is a
byproduct of this reaction.
2. Combustion. Carbon also returns to the atmosphere through
combustion, or burning. The carbon contained in wood may stay
there for many years, returning to the atmosphere only when the
wood is burned. Sometimes carbon can be locked away beneath
the Earth for thousands or even millions of years. The remains of
organisms that become buried in sediments may be gradually
transformed by heat and pressure into fossil fuels—coal, oil, and
natural gas. The carbon is released when the fossil fuels are burned.
3. Erosion. Marine organisms use carbon dioxide dissolved in sea
water to make calcium carbonate shells. Over millions of years,
the shells of the dead organisms form sediments, which form
limestone. As the limestone becomes exposed and erodes, the
carbon becomes available to other organisms.
Cellularrespiration
Combustion
Photosynthesis
Death anddecomposition
Fossil fuels
Limestone
Marineplanktonremains
Carbon dioxide (CO2)in atmosphere
Dissolved
CO2
in
water
This diagram shows the major
steps of the carbon cycle.
Figure 13 Carbon cycle
352
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Trends in AgricultureCrop Rotation Farmers often rotate a nonleguminous crop, such as corn, with a legu-minous one, such as alfalfa. The alfalfa will fixnitrogen and release some of it into the soil. Ifa crop of alfalfa is plowed back into the soil, itmay add as much as 350 kg (770 lb.) of nitro-gen per hectare (2.5 acres) of soil, enough togrow a crop of nonleguminous plants withoutthe need for additional fertilizer.
DemonstrationTell students that beans are legumi-nous plants, the roots of whichhave nodules containing nitrogen-fixing bacteria. Then tell them thatother such plants include clover,peas, alfalfa, lupines, and locustand alder trees. If any of theseplants are available nearby, see ifyou can dig up an example to showthe class any nodules that may bepresent. Visual
Teaching TipGene Splicing Only some typesof plants have the symbiotic rela-tionship with nitrogen-fixing bacteria that enables them to con-vert nitrogen gas into a usable formof nitrogen. Scientists are workingto isolate and remove the “nitro-gen-fixing gene” in hopes they cansplice it into other types of plantsand make them nitrogen fixers aswell. Have students discuss thepros and cons of doing this. (pro—reduce amount of fertilizerneeded, tremendous economic impact;this could help feed starving peoplesin countries with poor agriculturalresults; con—no one knows for surewhat will happen with a new,genetically-engineered organism)
Using the FigureHave students study Figure 14.Point out the difference betweennitrogen fixation (nitrogengas➞ammonia) and nitrification(ammonia➞nitrates). Tell studentsthat lightning also changes nitrogengas to ammonia, but such atmos-pheric action amounts to less than10 percent of that carried out byorganisms through nitrogen fixation.Finally, have students recognize thatdenitrification returns nitrates to the atmosphere as nitrogen gas.
LogicalLS
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Chapter 16 • Ecosystems 353
The Phosphorus and Nitrogen CyclesOrganisms need nitrogen and phosphorus to build proteins and
nucleic acids. Phosphorus is an essential part of both ATP and DNA.
Phosphorus is usually present in soil and rock as calcium phosphate,
which dissolves in water to form phosphate ions, PO43-. This phos-
phate is absorbed by the roots of plants and used to build organic
molecules. Animals that eat the plants reuse the organic phosphorus.
The atmosphere is about 78 percent nitrogen gas, N2. However,
most organisms are unable to use it in this form. The two nitrogen
atoms in a molecule of nitrogen gas are connected by a strong triple
covalent bond that is very difficult to break. However, a few bacteria
have enzymes that can break it, and they bind nitrogen atoms to
hydrogen to form ammonia, NH3. The process of combining nitro-
gen with hydrogen to form ammonia is called .
Nitrogen-fixing bacteria live in the soil and are also found within
swellings, or nodules, on the roots of beans, alder trees, and a few
other kinds of plants.
The nitrogen cycle, diagramed in Figure 14, is a complex process
with four important stages.
1. Assimilation is the absorption and incorporation of nitrogen
into organic compounds by plants.
2. Ammonification is the production of ammonia by bacteria dur-
ing the decay of organic matter.
3. Nitrification is the production of nitrate from ammonia.
4. Denitrification is the conversion of nitrate to nitrogen gas.
nitrogen fixation
Reviewing Information
Using your own words, write
four sentences, each one
describing one of the four
biogeochemical cycles.
Denitrification
AssimilationNitrogenfixation
Nitrification Nitrogenfixation
Ammonification
Nitrogen-fixingbacteria inplant roots
Nitrogen-fixingbacteria in soil
Nitrifyingbacteria
Denitrifyingbacteria
Atmosphericnitrogen (N2)
Animals
Death Death
Plants
Ammonia (NH3)
Nitrates(NO3)
Waste(urine and feces)
Decomposers
Bacteria carry out many of
the important steps in the
nitrogen cycle, including the
conversion of atmospheric
nitrogen into a usable form,
ammonia.
Figure 14 Nitrogen cycle
353
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ReteachingAsk students to write a short essaydescribing what the world wouldlook like without fungi or bacteria.
QuizTrue or False:
1. Of all the abiotic components ofan ecosystem, water has thegreatest influence on the ecosys-tem’s inhabitants. (true)
2.Carbon is necessary forphotosynthesis. (true)
AlternativeAssessmentHave students select a biogeochemi-cal cycle (except the water cycle).Being specific and writing in essayform, they should explain howhumans would be affected if theirchosen element did NOT cycle.
GENERAL
CloseClose
Answers to Section Review
1. The sun’s heating causes wind currents, whichdraws moisture from plant leaves.
2. Carbon and energy both move through ecosystems. Light energy is captured by photo-synthesizers and used to make organic moleculesusing carbon dioxide. Energy flows out ofecosystems mainly as heat during cellular respi-ration and combustion. These processes alsorelease carbon, but it does not “leave” theecosystem; photosynthesizers recycle it.
3. Nitrogen-fixing bacteria convert nitrogen gasto ammonia. Nitrifying bacteria convertammonia to nitrates, also usable by some
plants. Denitrifying bacteria turn the nitratesinto nitrogen gas.
4. Nutrients can cycle because they are in a formusable by at least some organisms, which keepsthe nutrient moving through (but still within)the ecosystem. Most energy, on the other hand,only flows in one direction. By the end of thefood chain, nearly all the original energy hasbeen “lost” as unusable heat.
5. A. Incorrect. Combustion puts CO2 into theatmosphere. B. Incorrect. This process putsCO2 into the atmosphere. C. Incorrect. Erosionputs CO2 into the atmosphere. D. Correct.
354 Chapter 16 • Ecosystems
Sustainable AgricultureOrganic farming is a form ofsustainable agriculture that doesnot use chemical fertilizers orpesticides. Ask students if theythink this would lead to biggerprofits for farmers. (It may beless profitable in the short term,but in the long run, they maycome out ahead because they willhave healthy soil and will not beusing costly fertilizers.)
Teach, continuedTeach, continued
The growth of plants in ecosystems is often limited by the
availability of nitrate and ammonia in the soil. Today most of the
ammonia and nitrate that farmers add to soil is produced chemi-
cally in factories, rather than by bacterial nitrogen fixation. Genetic
engineers are trying to place nitrogen-fixing genes from bacteria
into the chromosomes of crop plants. If these attempts are successful,
the plants themselves will be able to fix nitrogen, thus eliminating the
need for nitrogen-supplying fertilizers. Some farmers adjust their
farming methods to increase natural recycling of nitrogen.
Sustainable Agriculture
In an ecosystem, decomposers
return mineral nutrients to the
soil. However, when the plants are
harvested and shipped away,
there is a net loss of nutrients from
the soil where the plants were
growing. The amount of organic
matter in the soil also decreases,
making the soil less able to hold
water and more likely to erode.
What is SustainableAgriculture?
Sustainable agriculture refers to
farming that remains productive
and profitable through practices
that help replenish the soil’s
nutrients, reduce erosion, and
control weeds and insect pests.
Use of Cover Crops
After harvest, farmers can plant
cover crops, such as rye, clover,
or vetch, instead of letting the
ground lie bare. Cover crops
keep the soil from compacting
and washing away, and they help
the soil absorb water. They also
provide a habitat for beneficial
insects, slow the growth of
weeds, and keep the ground
from overheating. When cover
crops are plowed under, as illus-
trated in the figure at right, they
return nutrients to the soil.
Rotational Grazing
Farmers who raise cattle and
sheep can divide their pastures
into several grazing areas. By
rotating their livestock from one
area to another, they can prevent
the animals from overgrazing the
pasture. This allows the plants
on which the animals feed to
live longer and be more produc-
tive. Water quality improves as
the pasture vegetation becomes
denser. Animals distribute manure
more evenly with rotational
grazing than they do in feed lots
or unmanaged pastures.
There are many other methods
used in sustainable agriculture.
Farmers must determine which
methods work best for their crops,
soil conditions, and climate.
www.scilinks.org
Topic: Sustainable Agriculture
Keyword: HX4170
Identify the role of energy in the part of thewater cycle in which plants transfer water to theatmosphere.
Analyze the carbon cycle’s relationship to theflow of energy.
Describe how bacteria participate in thenitrogen cycle.
Critical Thinking Defend the argument thatnutrients can cycle but energy cannot.
Which component of thecarbon cycle removes carbon dioxide from theatmosphere?
A combustion C erosion
B cellular respiration D photosynthesis
Standardized Test PrepStandardized Test Prep
Section 3 Review
354
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Alternative Assessment Have students choose an ecosystemfrom anywhere in the world. (Forexample, students could choose theCosta Rican rain forest, SonoranDesert, Kalahari Plain, or FloridaEverglades.) Have them researchand report on the biotic and abioticcomponents. Tell them to includedescriptions of four producers,three herbivores, two small carni-vores, one top carnivore, and onedetritivore. Have them draw a foodchain, food web, and energy pyra-mid for this ecosystem.
Answer to Concept Map
The following is one of several possible answers to Performance Zone item 15.
Chapter 16 • Ecosystems 355
GENERAL
• Science Skills Worksheet
• Critical Thinking Worksheet
• Test Prep Pretest
• Chapter Test GENERAL
GENERAL
GENERAL
Chapter Resource File
contains several
composed of
which contain
are
areare prey for
feedon
Food web
food chains
trophic levels
producers
carnivores consumers
herbivores detritivores
Key Concepts
Study CHAPTER HIGHLIGHTS
ZONE
Key Terms
Section 1
ecology (340)
habitat (340)
community (340)
ecosystem (340)
abiotic factor (340)
biotic factor (340)
biodiversity (341)
pioneer species (343)
succession (343)
primary succession (343)
secondary succession (343)
Section 2
primary productivity (345)
producer (345)
consumer (345)
trophic level (345)
food chain (346)
herbivore (346)
carnivore (346)
omnivore (346)
detritivore (346)
decomposer (347)
food web (347)
energy pyramid (348)
biomass (349)
Section 3
biogeochemical cycle (350)
ground water (351)
transpiration (351)
nitrogen fixation (353)
BIOLOGYBIOLOGY
Unit 7—Ecosystem Dynamics
Use Topics 1, 3–6 in this unit to review the
key concepts and terms in this chapter.
What Is an Ecosystem?
● Ecology is the study of how organisms interact with each
other and with their environment.
● A community of organisms and their nonliving environment
constitute an ecosystem.
● Ecosystems contain diverse organisms.
● Ecosystems change through the process of succession.
● Succession on a newly formed habitat is primary succession.
● Secondary succession occurs on a habitat that has previously
supported growth.
Energy Flow in Ecosystems
● Energy moves through communities in food chains, passing
from photosynthesizers (producers) to herbivores (consumers)
to carnivores (consumers), creating a food web.
● Energy transfers between trophic levels transfer only 10
percent of the energy in a trophic level to the next level.
● Most terrestrial communities have only three or four trophic
levels because energy transfers between trophic levels are
inefficient.
Cycling of Materials in Ecosystems
● Minerals and other materials cycle within ecosystems among
organisms and between organisms and the physical environment.
● In the water cycle, water falls as precipitation and either
evaporates from bodies of water, is stored in ground water,
or cycles through plants and then evaporates.
● Carbon enters the living portion of the carbon cycle through
photosynthesis. Organisms release carbon through cellular
respiration. Carbon trapped in rocks and fossil fuels is
released by erosion and burning.
● Bacteria fix atmospheric nitrogen, thus making ammonia
available to other organisms.
3
2
1
355
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ANSWERS
Understanding Key Ideas
1. b
2. b
3. c
4. d
5. b
6. c
7. Greater flexibility in diet allowsomnivores to eat whatever foodis available.
8. Plowing the corn into the fieldwould return organic matter andnutrients to the soil—a more sus-tainable approach.
9. Photosynthesis enables plants to incorporate nitrogen intoproteins, making it available toconsumers. When consumersexcrete waste or decompose,plants (with the aid of bacteria)may take up the nitrogen again,completing the cycle.
10. One possible answer to the con-cept map is found at the bottomof the Study Zone page.
Critical Thinking
11. Each trophic level contains about90% less energy than the levelbelow it. If 1,000 kilocalories ofseeds were eaten by a mouse, itwould result in about 100 kilo-calories for the snake that eatsthe mouse. And there would onlybe about 10 kilocalories availablefor the hawk that eats the snake.
12. Many pioneer organisms, such aslichens, have the ability to fixnitrogen, but all pioneer plantsare able to fix carbon duringphotosynthesis. Therefore, nitro-gen cycling is probably more
important to a pioneer species during primarysuccession.
13. Dead organisms and wastes would not decayand nutrients would not be recycled back intothe ecosystem.
Alternative Assessment
14. Answers will vary depending on the organ-isms pictured.
356 Chapter 16 • Ecosystems
CHAPTER 16
Section Questions
1 1, 3, 11, 12, 14
2 2, 5, 6, 7, 10, 13
3 4, 8, 9, 12
Assignment Guide
Understanding Key Ideas
1. Ecosystems differ from communities inthat ecosystems usually containa. several climates. b. several communities. c. only one habitat. d. only one food web.
2. What critical role is played by fungi andbacteria in any ecosystem? a. primary productionb. decompositionc. boundary settingd. physical weathering
3. Which sequence shows the correct order ofsuccession at Glacier Bay, Alaska?a. alder, Dryas, hemlockb. Dryas, hemlock, alderc. Dryas, alder, Sitka spruced. mosses, hemlock, Sitka spruce
4. Which role is not performed by bacteria inthe nitrogen cycle? a. fixing nitrogenb. changing urea to ammoniac. turning nitrates into nitrogen gasd. changing nitrates to ammonia
5. How would the food web below be affectedif the plants were eliminated?
a. Herbivores would become carnivores. b. The food web would collapse. c. The herbivores would change trophic levels.
d. Nothing would happen.
6. How much energy is available at the third trophic level of an energy pyramid if1,000 kcal is available in the first level? a. 1,000 kcal c. 10 kcalb. 100 kcal d. 1 kcal
7. Humans, raccoons, and bears areomnivores. What adaptive advantage might this feeding strategy provide?
8. After harvesting, a farmercould either plow the remaining cornstalksinto the field or burn them. Which optionis best for sustainable agriculture? Explainyour answer.
9. Relate photosynthesis to the nitrogen cycle.(Hint: See Chapter 5, Section 2.)
10. Concept Mapping Make a conceptmap that describes the flow of energythrough an ecosystem. Try to include thefollowing terms in your map: trophic level,food web, food chain, producer, consumer,carnivore, detritivore, and herbivore.
Critical Thinking
11. Inferring Relationships Analyze the flow ofenergy between an ecosystem and one of itstop carnivores, such as a hawk.
12. Applying Information Is nitrogen cycling orcarbon cycling more important to a pio-neer species during primary succession?Explain your answer.
13. Predicting Results Describe the probableeffects on an ecosystem if all decomposerswere to die.
Alternative Assessment
14. Identifying Functions Obtain photocopiesof nature paintings by American painterssuch as John James Audubon or EdwardHicks. Choose three animals, and write areport that compares the animals, theecosystems in which they live, their roles inbiogeochemical cycles, and the trophiclevel they occupy.
PerformanceZONE
CHAPTER REVIEW
356
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Question 5 Answer D is the cor-rect choice. Transpiration involveswater evaporating from a plant’sleaves and entering the atmos-phere. Answer A is incorrectbecause assimilation involvesnitrogen being absorbed by plantsto make organic compounds anddoes not return water directly tothe atmosphere. Answer B is incor-rect because nitrification is theproduction of nitrates from ammo-nia and does not return waterdirectly to the atmosphere. AnswerC is incorrect because successioninvolves the cycling of entireorganisms in an ecosystem, notjust water.
Question 6 Changes in climate,large-scale disturbances such asfire or volcanic eruption, and evenchanges in biotic factors such asan insect pest outbreak can changethe conditions of an ecosystem.
Question 7 Answer H is the cor-rect choice. Answer F is incorrectbecause algae do not necessarilyharm meadow grasses. Answer Gis incorrect because the presence ofdecaying organic matter is benefi-cial to most plants, as it providesnutrients for the soil. Answer I isincorrect because, as the ecosystemmatures, meadow grasses eventu-ally crowd out the marsh plants.
Question 8 Answer C is the cor-rect choice. The lowest level ofcarbon dioxide indicates the great-est rate of photosynthesis. AnswerA is incorrect because the carbondioxide level is highest in January.Answer B is incorrect becauseMarch shows a higher carbondioxide level than May. Answer Dis incorrect because Septembershows a higher carbon dioxidelevel than May.
Answers
1. C
2. I
3. B
4. F
5. D
6. Ecosystems are dynamic by nature.
7. H
8. C
Chapter 16 • Ecosystems 357
Standardized Test Prep
Understanding ConceptsDirections (1–5): For each question, write ona separate sheet of paper the letter of thecorrect answer.
1 Which of the following situationsdescribes a carnivore and an herbivore?A. A horse eats an apple.B. A rabbit eats a dandelion.C. A mountain lion eats a rabbit.D. A fungus breaks down a dead oak tree.
2 What term applies to most humans?F. carnivore H. herbivoreG. detrivore I. omnivore
3 What is an organism that obtains energyfrom organic wastes and dead bodiescalled?A. carnivore C. herbivoreB. detrivore D. omnivore
4 What is the process by which materialspass between the nonliving environmentand living organisms?F. biogeochemical cycleG. energy pyramidH. food webI. primary succession
5 Through what process do plants returnwater to the atmosphere?A. assimilationB. nitrificationC. successionD. transpiration
Directions (6): For the following question,write a short response.
6 Ecologists once referred to stable ecosys-tems as a final or climax community. Nowmost ecologists say that no ecosystem cantruly have a final end point. Analyze whyecologists have changed their viewpoint.
Reading SkillsDirections (7): Read the passage below.Then answer the question.
Artificial ecosystems used in the treatment of waste water and pollutants can demonstrate succession. Artificial wastewater-treatment ecosystems tend to undergo eutrophication, just as natural wetlands do. However, the high nutrient levels in waste water promote rapid algae growth. If the systems are not manipulated, they will eventually fill with algae and decay-ing organic matter, providing nutrients for other species. The system can then form a marsh and eventually a meadow.
7 Why don’t meadow grasses populate thenew ecosystem before the marsh plantsand algae begin to grow there?F. The presence of algae is harmful tomeadow grasses.
G. The presence of decaying organic matter is harmful to meadow grasses.
H. Meadow grasses require that pioneerspecies first make nutrient-rich soil.
I. Meadow grasses cannot compete withmarsh plants in established ecosystems.
Interpreting GraphicsDirections (8): Base your answer to question8 on the graph below.
Atmospheric Carbon Dioxide Variation
8 During which of the following months isthe rate of photosynthesis greatest?A. January C. MayB. March D. September
Carbon dioxide concentration
(pa
rts p
er
mill
ion
)
Month
March May July Sept.Jan. Nov.
348
350
352
354
356
358
Test
For multiple-choice questions, try to eliminate any
answer choices that are obviously incorrect, and
then consider the remaining answer choices.
357
Standardized Test Prep
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Exploration Lab
MODELING ECOSYSTEM
CHANGE OVER TIME
Teacher’s Notes
Time Required About20 minutes on day 1 and about10 minutes each day thereafter over a period of a few weeks.
Ratings
TEACHER PREPARATION
STUDENT SETUP
CONCEPT LEVEL
CLEANUP
Skills Acquired• Collecting Data• Constructing Models• Organizing and Analyzing Data
Scientific MethodsIn this lab, students will:• Make Observations• Test the Hypothesis• Analyze the Results
Materials and EquipmentMaterials for this lab can beordered from WARD’S. See MasterMaterials List at the front of thisbook for catalog numbers. Havestudents bring clear plastic 2- or 3-L soda bottles from home. Soilcan be collected from around theschool, brought from home, or pur-chased from a garden center. Youmay also be able to find earth-worms and crickets in the localenvironment or at bait shops.
Safety CautionsReview all safety symbols with stu-dents before beginning the lab.Warn students to take care whenhandling insects and other smallanimals. Small animals are easilyharmed, and some are capable ofbiting when disturbed.
E A S Y H A R D
Tips and TricksRemind students that the ecosystems aredependent on humans for care. They shouldnot be permitted to be overheated or becometoo cold. If water evaporates from the ecosys-tem, it should be replenished. Recording thenumber of organisms may be tricky in somecases and estimates may be required.
Answers to Before You Begin1. ecosystem—an ecological system encompassing
a community and its abiotic factors; food web—a network of feeding relationshipsin an ecosystem; closed ecosystem—an ecosys-tem that does not exchange materials outsideof itself; producer—organisms that first cap-ture energy; decomposer—organisms thatdecompose dead organic material; consumer—organisms that consume producers;herbivore—organisms that eat plants or otherprimary producers; carnivore—organisms thatare secondary consumers; trophic level—ecosystem level based on the organism’s sourceof energy.
358 Chapter 16 • Ecosystems
Before You Begin
Organisms in an interact with
each other and with their environment. One
of the interactions that occurs among the
organisms in an ecosystem is feeding. A
describes the feeding relationships
among the organisms in an ecosystem. In
this lab, you will model a natural ecosystem
by building a in a bottle
or a jar. You will then observe the interac-
tions of the organisms in the ecosystem and
note any changes that occur over time.
1. Write a definition for each boldface term in
the paragraph above and for each of the
following terms: producer, decomposer,
consumer, herbivore, carnivore, trophic
level.
2. Based on the objectives for this lab, write a
question you would like to explore about
ecosystems.
Procedure
PART A: Building an Ecosystem in a Jar
1. Place 2 in. of sand or pea gravel in
the bottom of a large, clean glass jar
with a lid. CAUTION: Glassware is fragile.
Notify your teacher promptly of any
broken glass or cuts. Do not clean up
broken glass or spills with broken glass
unless your teacher tells you to do so.
Cover the gravel with 2 in. of soil.
2. Sprinkle the seeds of two or three types of
small plants, such as grasses and clovers,
on the surface of the soil. Put a lid on the
jar, and place it in indirect sunlight. Let the
jar remain undisturbed for a week.
3. After one week, place a handful of rolled
oats into the jar. Place the mealworms in
the oats, and then place the other animals
into the jar and replace the lid. Place the
lid on the jar loosely to enable air entry.
You ChooseAs you design your experiment, decide the following:
a. what question you will explore
b. what hypothesis you will test
c. how you will plant the seeds
d. where you will place the ecosystem for oneweek so that it remains undisturbed and inindirect sunlight
e. how often you will add water to the ecosys-tem after the first week
f. how many of each organism you will use
g. what data you will record in your data table
closed ecosystem
web
food
ecosystem
Exploration Lab
Modeling Ecosystem Change over Time
SKILLS
• Using scientific methods
• Modeling
• Observing
OBJECTIVES
• Construct a model
ecosystem.
• Observe the interactions of
organisms in a model
ecosystem.
• Predict how the number
of each species in a model
ecosystem will change
over time.
• Compare a model
ecosystem with a natural
ecosystem.
MATERIALS
• coarse sand or pea gravel
• large glass jar with a lid or terrarium
• soil
• pinch of grass seeds
• pinch of clover seeds
• rolled oats
• mung bean seeds
• earthworms
• isopods (pill bugs)
• mealworms (beetle larva)
• crickets
358
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Answers to Do You Know?1. Biosphere 2 is a large artificial ecosystem near
Tucson, Arizona. The 204,000-m3 glass andsteel structure contains seven ecosystems. Thestructure has been used for research on thebiosphere, the sum of all of Earth’s ecosystems.
2. Answers will vary. Students should list severalexamples of problems, including food short-ages, oxygen shortages, and populationexplosions of microorganisms, ants, and cockroaches.
2. Answers will vary. For example,What are the effects of continuousexposure to bright light on theecosystem?
Part B: Sample Procedure1. Place the jar to the side of a win-
dow so that it receives indirectsunlight throughout the day.
2. After one week, add three earth-worms, five isopods, threemealworms, and three crickets tothe jar. Using a mister, add foursquirts of water per square decime-ter of soil surface every other day.
3. Record population data everyother day for two weeks.
Answer to Analyze andConclude1. Answers will vary. Students should
make one graph for each speciesobserved or use different colors toindicate each species.
2. Answers will vary.
3. Answer will vary. All plants areproducers (primary trophic level);earthworms feed on dead plantmaterial in the soil; crickets feedon plants; mealworms (beetle lar-vae) feed on plants; isopods (pillbugs) eat wood.
4. Yes and no. Natural ecosystemsand the model ecosystem bothcontain organisms at severaltrophic levels, have living and non-living components, and depend onthe sun for energy. However, themodel ecosystem is less diverse,much younger, and has more defi-nite boundaries than a naturalecosystem.
5. Answers will vary.
6. No. Strengths are that the organ-isms in the model ecosystem didnot leave the ecosystem and thatother organisms could not enterfrom the outside. Weaknesses arethat water and air probably had tobe added to maintain a healthyecosystem.
7. Answers will vary. For example:What are the effects of certain abi-otic factors, such as temperature,light, and moisture, on the organ-isms in an ecosystem?
Chapter 16 • Ecosystems 359
PART B: Design an Experiment
4. Work with the members of your lab group
to explore one of the questions written for
step 2 of Before You Begin. To explore the
question, design an experiment that uses
the materials listed for this lab.
5. Write a procedure for your experiment.
Make a list of all the safety precautions you
will take. Have your teacher approve your
procedure and safety precautions before
you begin the experiment.
6. Set up your group’s experiment. Conduct
your experiment for at least 14 days.
PART C: Cleanup and Disposal
7. Dispose of solutions, broken glass,
and other materials in the designated
waste containers. Do not put lab materials
in the trash unless your teacher tells you to
do so.
8. Clean up your work area and all lab
equipment. Return lab equipment to
its proper place. Wash your hands thor-
oughly before you leave the lab and after
you finish all work.
Analyze and Conclude
1. Summarizing Results Make graphs
showing how the number of individuals of
each species in your ecosystem changed
over time. Plot time on the x-axis and the
number of organisms on the y-axis.
2. Analyzing Results How did your results
compare with your hypothesis? Explain
any differences.
3. Inferring Conclusions Construct a food
web for the ecosystem you observed.
4. Recognizing Relationships Does your
model ecosystem resemble a natural
ecosystem? Explain.
5. Analyzing Methods How might you have
built your model ecosystem differently to
better represent a natural ecosystem?
6. Evaluating Methods Was your model
ecosystem truly a “closed ecosystem”? List
your model’s strengths and weaknesses as a
closed ecosystem.
7. Further Inquiry Write a new question
about ecosystems that you could explore
with another investigation.
www.scilinks.org
Topic: Ecosystems
Keyword: HX4066
Do You Know?
Do research in the library or media center
to answer these questions:
1. What is Biosphere 2?
2. What problems were encountered by
the Biosphere 2 crew during the
1991–1993 project?
Use the following Internet resources
to explore your own questions about
ecosystems.
359
Copyright © by Holt, Rinehart and Winston. All rights reserved.