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. When feces, 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. In general, 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 adds as much carbon dioxide to the atmosphere as photosyn- thesis removes. Human activities such as the burning of fossil fuels and trees adds carbon dioxide to the atmos- phere. Carbon dioxide and other gases trap heat, leading to global warming. The effects of global warming could be a rise in sea level and a change in climate patterns, with disastrous effects. In the nitrogen cycle, the biotic community keeps nitrogen recycling back to producers. Human activities convert 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 water vapor to form acids that contribute to acid deposition. Acid deposition is killing lake s and forests, and it also cor- rodes marble, metal, and stonework. Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN. These oxidants are harmful to animal and 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 of rocks. Phosphates are mined for fertilizer production, and 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 in decreased productivity of the oceans. Tropical rain forests are being destroyed in numerous ways, and many organisms that could possibly benefit humans are threat- ened. Conservation biology is a new discipline that pulls together information from a number of biological fields to determine how to manage ecosystems for the ben- efit of all species. 307 36 ECOSYSTEMS AND HUMAN INTERFERENCES CHAPTER REVIEW STUDY EXERCISES (P . 744) Study the text section by section as you answer the questions that follow.
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Questions 7–10 are based on the following diagram:
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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. ___________________________________________________
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.
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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. ________________
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: _________________