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An ecosystem is a community of organisms plus the phys-

ical and chemical environment. Some populations are

producers and some are consumers. Producers are au-

totrophs that produce their own food. Consumers are het-

erotrophs that take in preformed food. Consumers may

be herbivores, carnivores, omnivores, or decomposers.

Energy flows through an ecosystem. Producers

transform solar energy into food for themselves and all

consumers. As herbivores feed on plants and carnivores

feed on herbivores, energy is converted to heat. Whenfeces, urine, and dead bodies become food for decom-

posers, all the solar energy that enters an ecosystem is con-

verted to heat. Therefore, ecosystems require a continual

supply of solar energy.

Chemicals are not lost from the biosphere. They

recycle within and between ecosystems. Decomposers

return some portion of inorganic nutrients to autotrophs,

and other portions are imported of exported between

ecosystems in global cycles.

The food webs of ecosystems contain grazing food

chains (begin with a producer) and detrital food chains

(begin with detritus). A trophic level includes all the or-

ganisms that feed at a particular link in food chains. Ingeneral, biomass and energy content decrease from one

trophic level to the next as is depicted in an ecological

pyramid.

The global cycling of inorganic elements involves

the biotic and abiotic parts of an ecosystem. Cycles usu-

ally contain (1) a reservoir (a source normally unavail-

able to organisms), (2) a pool (a source available to

organisms), and (3) the biotic community.

In the water cycle, evaporation of ocean waters

and transpiration from plants contributes to aerial mois-

ture. Rainfall over land results in bodies of fresh water

plus ground water. Eventually all water returns to the

oceans.

In the carbon cycle, respiration by organisms add

as much carbon dioxide to the atmosphere as photosyn

thesis removes. Human activities such as the burning o

fossil fuels and trees adds carbon dioxide to the atmos

phere. Carbon dioxide and other gases trap heat, leadin

to global warming. The effects of global warming coul

be a rise in sea level and a change in climate patterns, wit

disastrous effects.

In the nitrogen cycle, the biotic community keep

nitrogen recycling back to producers. Human activitieconvert atmospheric nitrogen to fertilizer, which when bro

ken by soil bacteria adds nitrogen oxides to the atmos

phere. Nitrogen oxides and sulfur dioxide react with wate

vapor to form acids that contribute to acid deposition

Acid deposition is killing lakes and forests, and it also cor

rodes marble, metal, and stonework. Nitrogen oxides an

hydrocarbons (HC) react to form smog, which contain

ozone and PAN. These oxidants are harmful to animal an

plant life.

In the phosphorus cycle, the biotic community re

cycles phosphorus back to the producers, and only lim

ited quantities are made available by the weathering o

rocks. Phosphates are mined for fertilizer productionand fertilizers overenrich lakes and ponds.

Global warming, acid deposition, and water pol

lution reduce biodiversity. Ozone shield destruction

which is associated with CFCs, is expected to result i

decreased productivity of the oceans. Tropical rai

forests are being destroyed in numerous ways, and man

organisms that could possibly benefit humans are threat

ened. Conservation biology is a new discipline tha

pulls together information from a number of biologica

fields to determine how to manage ecosystems for the ben

efit of all species.

307

36ECOSYSTEMS AND HUMAN

INTERFERENCES

CH A P T E R RE V I E W

STUDY EX E R C I S E S (P. 744)

Study the text section by section as you answer the questions that follow.



308

36.1 THE NATURE OF ECOSYSTEMS (P. 744)

• An ecosystem is a community of organisms along with its physical and chemical environment.

• Autotrophs make their own food; photoautotrophs carry on photosynthesis. Heterotrophs, on the other hand,

take in preformed food.

• Solar energy enters biotic communities via photosynthesis, and as organic molecules pass from one organism

to another, heat is returned to the atmosphere.

• Chemicals cycle within and between ecosystems in global biogeochemical cycles.

1. Match the description with the following terms:1 carnivores

2 consumers

3 decomposers

4 herbivores

5 omnivores

6 autotrophs

a. organisms of decay

b. feed only on other animals

c. producers in an ecosystem

d. heterotrophs eating preformed food

e. feed directly on green plants

f. feed on both plants and animals

2. Fill in the diagram with the following terms: decomposers, consumers, producers, inorganic nutrient pool

sun

heat

a. _____________

heat

heat

b. ______________

d. _____________c. ______________

heat

3. Energy (solid arrows in diagram for question 2) doesn’t cycle in an ecosystem. Explain on the basis of the

second law of thermodynamics. a. _____________________________________________________________

Chemicals (open arrows in diagram) do cycle in an ecosystem. Explain by referring to the diagram. b. _______

________________________________________________________________________________________



Questions 4–6 are based on the following diagram:

309

4. From this food web, formulate a grazing food chain.

_______________________________________________________________________________________

5. From this food web, formulate a detritus food chain.

_______________________________________________________________________________________

6. Explain one way in which the detritus food web and the grazing food web are always connected.

_______________________________________________________________________________________

Grazing food web

Detritus food web

fruits and nuts

leaves

old leaves,dead twigs

deer

rabbits

leaf-eatinginsects

mice

chipmunks

birds

bacteria and fungi

detritus

invertebrates

carnivorous

invertebrates

shrews

salamanders

foxes

fishers

skunks

owls

snakes

hawks



producers

herbivores

carnivores

top carnivores

Questions 7–10 are based on the following diagram:

310

7. Each level of a pyramid represents a trophic level. With reference to the grazing food web, name an organismat the first trophic level. a. __________________ Two organisms at the second t rophic level.b. __________________ Two organisms a t the third trophic level. c. __________________

8. With reference to a pyrmid of energy, why is each trophic level reduced in size? a. __________________ Why is

there a limited number of trophic levels? b. __________________

36.2 GLOBAL BIOGEOCHEMICAL CYCLES (P. 748)

• Biogeochemical cycles are gaseous (carbon cycle, nitrogen cycle) or sedimentary (phosphorus cycle)

• The addition of carbon dioxide (and other gases) to the atmosphere is associated with global warming.

• The production of fertilizers from nitrogen gas is associated with acid deposition, photochemical smog, and

temperature inversions.

• Fertilizer also contains mined phosphate; fertilizer runoff is associated with water pollution.

9. Examine the following diagram and then answer the questions:

r p

o d u

c e r s

d e c o m

p o s e r s

c o n s u m e r s

reservoir exchangepool

bioticcommunity

atmospheresoil

water

fossil fuelsmineral in rocks

sediment in oceans

human activities

What is a reservoir? a. ______________________________________________________________________

What is an exchange pool? b. _________________________________________________________________

What is a biotic community? c. _______________________________________________________________

Explain the arrows labeled human activities. d. ___________________________________________________

________________________________________________________________________________________



The Water Cycle (p. 749)

10. Complete this diagram of the water cycle by: filling in the boxes, using these terms: ice, H 2O in the

atmosphere, ocean, groundwaters

labeling the arrows, using these terms: precipitation (twice), transpiration from plants and evaporation from

soil, evaporation, transport of water vapor by wind.

31

11. Select the statements that are true about the water cycle.

a. Water cycles between the land, the atmosphere, and the ocean and vice versa.

b. We could run out of fresh water.

c. The ocean receives more precipitation than the land.

d. Water that is in the aquifers never reaches the oceans.

The Carbon Cycle (p. 750)

12. In the carbon cycle, carbon dioxide is removed from the atmosphere by the process of a. ____________ but is

returned to the atmosphere by the process of b. ____________ Living things and dead matter in soil are carbonc. ____________ and so are the d.____________ because of shell accumulation. In aquatic ecosystems, carbon

dioxide from the air combines with water to produce e. ______________ that algae can use for photosynthesis

In what way do humans alter the exchange rates in the carbon cycle? f. ________________

f.

c.

e.

runoff

b.

h.i.

g.

a.

d.

lake

aquifer



13. Fill in the table to indicate the source of gases that cause the greenhouse effect:

Gas From

Carbon dioxide (CO2) a. ______________________________________________________________

Nitrous oxide (N2O) b. ______________________________________________________________

Methane (CH4) c. ______________________________________________________________

Why are these gases called the greenhouse gases?d.

____________________________________________________________________________________________________________________________________________________

14. Place an x beside all those statements that may be expected because of global warming.

a. a global temperature increase by as much as 4.5˚ C

b. melting of glaciers and a rise in sea level

c. massive fish kills and plant destruction

d. dryer conditions inland where droughts may occur

e. expansion of forests into Arctic areas

The Nitrogen Cycle (p.752)

312

plants

dead organismsand animal waste

BIOTICCOMMUNITY BIOTIC

COMMUNITY

phyplank

decomposers

NO3–

NO3–

NO2–

NH4+

NH4+

sedimentation

cyanobacteria

denitrifying bacteria

nitrifying

bacteria

denitrifyingbacteria

N2 fixation

N2 fixation

nitrification

denitrificationdenitrification

runoff

humanactivities

decomposers

nitrogen-fixingbacteria in

nodules and soil

N2 IN ATMOSPHERE



Questions 15 and 16 are based on the following diagram:

15. Match the definitions with the following terms:

1 denitrifying bacteria

2 nitrifying bacteria

3 nitrogen-fixing bacteria

a. bacteria that convert nitrate to nitrogen gas.

b. bacteria that convert ammonium to nitrate

c. bacteria in legume nodules that convert nitrogen gas to ammonium

16. Plants cannot utilize nitrogen gas. What are two ways in which plants receive a supply of nitrogen for

incorporation into pro teins and nucleic acids? _______________________________________________________17. When humans produce fertilizers, the gas a. ____________ Is removed from the atmosphere and changed to

b. ____________, which enters the atmosphere. Acid deposit ion occurs when nitrogen oxides andc. ____________ in the atmosphere are converted to acids that re turn to Earth.

18. Place an x beside all those statements that may be expected because of acid deposition.

a. dying forests

b. lower agricultural yields

c. sterile lakes

d. corroded marble, metal and stonework

19. Photochemical smog arises when a. ____________ and b. ____________ react wi th one another in the presence o

sunlight. Smog contains the pollutants c. ____________ and d. ____________.

20. Place an x beside all those effects that may be expected from the occurrence of smog.

a. breathing difficultiesb. damage to plants

c. thermal inversions

d. cleaner air than usual

The Phosphorus Cycle (p.754)

21. Place a check in front of the statement(s) that describe(s) the results when producers take up phosphate.

a. become a part of phospholipids

b. becomes a part of ATP

c. becomes a part of nucleotides

d. become a part of the atmosphere

22. Indicate whether the statements that follow are true (T) or false (F). Rewrite all false statements to be true

statements.

a. Excess phosphate in bodies of water may cause radiation poisoning. Rewrite: _________________

________________________________________________________________________________

b. Most ecosystems have plenty of phosphate. Rewrite: _____________________________________

________________________________________________________________________________

c. The phosphorus cycle is a sedimentary cycle. Rewrite: ___________________________________

________________________________________________________________________________

d. Phosphate enters ecosystems by being taken up by animals. Rewrite: ________________________

________________________________________________________________________________

36.3 HUMAN IMPACT ON BIODIVERSITY (P. 7 56)

• Global warming, acid deposition, photochemical smog, water pollution, ozone depletion, and tropical rain

forest destruction are all involved in reducing biodiversity.

• Conservation biology is the scientific study of biodiversity and the management of ecosystems for the

preservation of all species, including Homo sapiens.

313



23. What is the ozone shield, and why is it important? ________________________________________________

________________________________________________________________________________________

24. Explain the significance of the following:

C1 + O3 → ClO + O2

________________________________________________________________________________________

25. What are some of the possible effects of increased ultraviolet radiation on humans and other organisms? ____

________________________________________________________________________________________

26. Explain how forest destruction causes each of the following:

loss of a CO2 sink a. ________________________________________________________________________

loss of biodiversity b. _______________________________________________________________________

loss of medicinal plants c. ___________________________________________________________________

27. What new area of biology is concerned with the preservation and management of ecosystems for

sustainability? ____________________________________________________________________________

CH A P T E R TE S T

314

OBJECTIVE QUESTIONS

Do not refer to the text when taking this test.

In questions 1–7, indicate whether the statements are true

(T) or false (F).

1. Energy flows through a food chain because it is

constantly lost from organic food as heat.

2. A food web contains many food chains.

3. An ecological pyramid is usually broadest at the

bottom and narrowest at the top.

4. The weathering of rocks is one way that phosphate

ions are made available to plants.

5. Respiration returns carbon to the atmosphere.

6. Nitrogen fixation is the return of nitrogen to the

atmosphere.

7. Denitrifying bacteria convert atmospheric ni-

trogen into the bodies of organisms.

8. About _______ of the energy available at a par-

ticular trophic level is incorporated into the tis-

sues at the next trophic level.

a. 1%

b. 10%

c. 25%

d. 50%

e. 75%

Questions 9–11 refer to the following food chain:

grass → rabbits → snakes → hawks.

9. Each population

a. is always larger than the one before it.b. supports the next level.

c. is an herbivore.

d. is a carnivore.

10. Rabbits are

a. consumers.

b. herbivores.

c. more plentiful than snakes.

d. All of these are correct.

11. Hawks

a. contain phosphate taken up by grass.

b. give off O2 that will be taken up by rabbits.

c. die and decompose and because of this they

cannot contribute to a grazing food chain.


12. Which of the following contribute(s) to the car-

bon cycle?

a. respiration

b. photosynthesisc. fossil fuel combustion


13. The largest reserve of unincorporated carbon is

in

a. the soil.

b. the atmosphere.

c. the ocean.

d. deep sediments.

14. The greenhouse effect

a. is caused by particles in the air.

b. is caused in part by carbon dioxide.

c. will cause temperatures to increase.

d. will cause temperatures to decrease.

e . Both b and c are correct.

15. The form of nitrogen most plants make use of is

a. atmospheric nitrogen.

b. nitrogen gas.

c. organic nitrogen.

d. nitrates.



315

For questions 16–18, match the air pollutants with the

following conditions:

a. ozone shield destruction

b. global warming

c. acid deposition

d. photochemical smog

16. CFCs

17. SO2

18. CO2

19. UV radiationa. causes mutations.

b. impairs crop growth.

c. kills plankton.


20. Nitrogen oxides and hydrocarbons react in the pres-

ence of sunlight to produce

a. acid particles.

b. ground level ozone.

c. greenhouse gases.


21. What may occur as a result of the greenhouse

effect?

a. coastal flooding

b. loss of food

c. excess plant growth

d. Both a and b are correct.

22. What contributes to the greenhouse effect?

a. nuclear power

b. burning of fossil fuels

c. geothermal energy

d. Both a and c are correct.

23. Which is the cause of stratospheric ozon

depletion?

a. chlorine

b . PANs

c. nitratesd. Both b and c are correct.

24. Acid deposition is associated with

a. dying lakes.

b. dying forests.

c. dissolving of copper from pipes.


THOUGHT QUESTIONS

Answer in complete sentences.

25. Why is a food chain normally limited to four or five links?

26. How would the shortage of an element in the exchange pool affect an ecosystem? Explain.

Test Results: ______ Number right ÷ 26 = ______ × 100 = ______ %

AN S W E R K E Y

STUDY EXERCISES

1. a. 3 b. 1 c. 6 d. 2 e. 4 f. 5 2. a. produces b. con-

sumers c. decomposers d. inorganic nutrient pool

3. a. With every transformation, as when the energy in

food is converted to ATP, there is always a loss of use-able energy. Eventually all solar energy taken in by plants

become heat. b. Plants take inorganic nutrients and pro-

duce organic nutrients; the inorganic nutrients are even-

tually returned to plants. 4. Example: nuts from tree

→ birds → hawks 5. Example: old leaves and dead

twigs → bacteria and fungi of decay → mice → hawk

6. Members of the grazing food web die and are decom

posed by bacteria and fungi. 7. a. Tree is the produce

b. Example: rabbits and deer c. Example: foxes an

snakes 8. a. Less energy is available to be passed on

b. Eventually energy runs out. 9. a. a source that is usu

ally unavailable to the biotic community b. a source tha

is usually available to the biotic community c. produc

ers, consumers, and decomposers that interact through nu

trient cycling and energy flow d. Humans remove element

from reservoirs and exchange pools and make them avail

able to producers. For example, humans convert nitroge



in the air to make fertilizer, and they mine phosphate to

make fertilizer. 10 . See Figure 36.8, p. 749 in text

11. a, b, c 12. a. photosynthesis b. cellular respiration

c. reservoirs d. oceans e. bicarbonate f. by burning fos-

sil fuels that add carbon to the atmosphere 13. a. fos-

sil fuel and wood burning b. fertilizer use and animal

wastes c. biogas (guts of animals, in sediments and in flooded

rice paddies d. These gases are called greenhouse gases

because, like the panes of a greenhouse, they allow solar

radiation to pass through but hinder the escape of heat.14. a, b, d, e 15. a. 1 b. 2 c. 3 16. nitrogen-fixing

bacteria in nodules and nitrate in soil 17. a. N2 b. NO3

c. sulfur dioxide 18. a, b, c, d 19. a. Nox b. HC c. PAN

d. ozone 20. a, b, c 21. a, b, c 22. a. F, . . . may

cause algal bloom b. F, . . . have a limited supply of phos-

phate c. T d. F, . . . taken up by plants 23. Ozone is a

layer within the stratosphere that protects the earth’s sur-

face from ultraviolet radiation. Organisms evolved in the

presence of this ozone layer. 24. The chlorine breaks

down the ozone and the UV radiation is not absorbed.

25. It will increase the incidence of skin cancer and de-

crease the productivity of living systems. Loss of oceanic

plankton will disrupt marine ecosystems. 26. see Fig-

ure 36.17, p. 757 in text 27. conservation biology.

CHAPTER TEST

1. T 2. F 3. T 4. T 5. T 6. F 7. F 8. b 9. b

10. d 11. a 12. d 13. c 14. e 15. d 16. a 17. c

18. b 19. d 20. b 21. d 22. b 23. a 24. d 25. By

the laws of thermodynamics, energy conversion at each

link of a food chain results in nonusable heat. Too little

useful energy remains for more links. 22. A shortage of

an element such as nitrogen or phosphorus would reduce

the biomass of the producer population. Therefore, the

biomass of each succeeding population in the ecosystem

would most likely be smaller than it otherwise would be.

316

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