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The biosphere consists of the atmosphere, the hydrosphere, and the lithosphere. All the ecosystems of the
world comprise the biosphere. An ecosystem is a community
of organisms plus the physical and chemical environment.
Some populations are producers and some are consumers.
Producers are autotrophs that produce their own organic
food. Consumers are heterotrophs that take in organic 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. Feces, urine,
and dead bodies become food for decomposers. Eventually, all the solar energy that enters an ecosystem is converted to heat, which dissipates. Therefore, ecosystems
require a continual supply of solar energy.
Inorganic nutrients are not lost from the biosphere
as energy is. Rather, they recycle within and between
ecosystems. Decomposers return some portion of inorganic nutrients to autotrophs, and other portions are imported or exported between ecosystems in global cycles.
The food webs of ecosystems include grazing food
chains (begin with a producer) and detrital food chains
(begin with detritus). A trophic level includes all the organisms that feed at a particular link in a food chain. 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 usually contain (1) a reservoir (a source normally unavailable to organisms), (2) an exchange pool (a source available
to organisms), and (3) the biotic community.
In the water (hydrologic) cycle, evaporation of
ocean waters and transpiration from plants contribute to
I-1 Ls itki is'
ES
atmospheric moisture. Rainfall over land results in bodies of fresh water and groundwater. Eventually, all water
returns to the oceans.
In the carbon cycle, respiration by organisms adds
as much carbon dioxide to the atmosphere as photosynthesis removes. Human activities, such as the burning of
fossil fuels and trees, add carbon dioxide to the atmosphere. Carbon dioxide and other gases trap heat, leading to global warming. Global warming could result in
a rise in sea level and a change in climate patterns, with
disastrous effects.
In the nitrogen cycle, the biotic community keeps
recycling nitrogen back to producers. Human activities convert atmospheric nitrogen to fertilizer, which when
broken down by soil bacteria adds nitrogen oxides to
the atmosphere. Nitrogen oxides and sulfur dioxide
react with water vapor to form acids that contribute to
acid deposition. Acid deposition is killing lakes and
forests, and it also corrodes marble, metal, and
stonework. Nitrogen oxides and hydrocarbons (HC)
react to form photochemical smog, which contains
ozone and PAN. These oxidants are harmful to animal
and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and only limited quantities are made available by the weathering of
rocks. Phosphates are mined for fertilizer production,
and fertilizer runoff can result in eutrophication of lakes
and ponds.
Global warming, acid deposition, and water pollution reduce biodiversity. Ozone shield depletion,
which is associated with CFCs, is expected to result in
decreased productivity of the oceans. The lack of an adequate ozone shield to absorb UV radiation could seriously affect health, food sources, and climate.
413
Study the text section by section as you answer the questions that follow.
• The biosphere encompasses those parts of the hydrosphere, atmosphere, and lithosphere where organisms live.
• In an ecosystem, organisms interact with one another and with the abiotic—that is, the chemical and
physical—environment.
• Autotrophs are self-feeders; photoautotrophs capture solar energy and produce organic nutrients.
Heterotrophs, on the other hand, take in preformed organic nutrients.
• Ecosystems are characterized by energy flow through populations and chemical cycling within and between
ecosystems.
1. Match the descriptions to these biotic components of an ecosystem:
omnivores
carnivores
consumers
decomposers
herbivores
organisms of decay
a.
feed only on other animals
b.
producers in an ecosystem
c.
heterotrophs
d.
feed directly on green plants
e.
f.
feed on both plants and animals
2. Label this diagram using these terms:
decomposers
consumers
producers
heat
autotrophs
inorganic nutrient pool
.
I
C.
/
heat
--')
-energy
—*nutrients
3. Energy doesn't cycle in ecosystems.
a. Which populations contain the most energy?
b. Which populations contain the least energy?
c. What happened to the energy? Explain on the basis of the second law of thermodynamics.
4 Chemicals do cycle in an ecosystem.
a. What two molecules do plants use to make glucose?
b. Glucose could conceivably pass from a producer population to the
populations.
populations to the
c. When the glucose is eventually broken down, what two substances are returned to plants?
414
• Energy flow between populations is represented by diagrams termed food webs and ecological pyramids.
Autotrophs
Herbivores/Omnivores
Carnivores
Moo
#/
fungi and bacteria
owls
)
invertebrates carnivorous invertebrates
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salamanders
shrews
b. Detritus food web
5. a. How many trophic levels do you see in the grazing portion of the food web diagram shown above?
b. Name a population at the first trophic level.
c. Name two populations at the second trophic level.
d. Name two populations at the third trophic level.
e. From these trophic levels, construct a grazing food chain.
6 Construct a detrital food chain from the food web diagram.
415
7. Explain one way in which the detrital food web and the grazing food web are always connected.
8. a. In the ecological pyramid shown above, name two populations from the food web diagram on page 415 that
are at the same level as the small fish.
b. In the ecological pyramid, name two populations at the same trophic level as the turtle.
9. a. Why is each higher trophic level smaller than the one preceding it?
b. What is the so-called 10% rule of thumb?
• Biogeochemical cycles are hydrologic (water cycle), 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,
thermal inversions, and ozone shield depletion.
• Fertilizer also contains mined phosphate; fertilizer runoff is associated with water pollution.
416
10. Examine the following diagram and then fill in the blanks.
human activities
os
06
.g
eo
< .
simmEn
excpt
oi ge
rese
biotic
community
t<
fossil fuels
mineral in rocks
sediment in oceans
a.
b.
c.
d.
atmosphere
soil
water
°sers
What is a reservoir?
What is an exchange pool?
What is a biotic community?
Explain the arrows labeled human activities.
11. Complete this diagram of the water cycle by filling in the boxes, using these terms:
ice H20 in the atmosphere ocean
groundwaters
Label the arrows using these terms:
precipitation (twice)
transpiration from plants and evaporation from soil
evaporation
transport of water vapor by wind
71.000
A
1.7
over land
13,000
8,200,000
12. Place a check beside the statements that correctly describe 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 in the aquifers never reaches the oceans.
417
13. Fill in the blanks. In the carbon cycle (not shown), carbon dioxide is removed from the atmosphere by the
. Living things
but is returned to the atmosphere by the process of b .
process of a.
because of shell accumulation.
and so are the d.
and dead matter in soil are carbon c.
that
In aquatic ecosystems, carbon dioxide from the air combines with water to produce e.
algae can use for photosynthesis. In what way do humans alter the transfer rates in the carbon cycle?
f.
14. Fill in the table to indicate the source of gases that cause the greenhouse effect.
Gas
From
Carbon dioxide (CO2)
a.
Nitrous oxide (N20)
b.
Methane (C H4)
C.
d. Why are these gases called the greenhouse gases?
15. Place a check beside all those statements that may be expected because of global warming.
a global temperature increase by as much as 4.5°C
a.
melting of glaciers and a rise in sea level
b.
massive fish kills and plant destruction
c.
drier conditions inland where droughts may occur
d.
expansion of forests into arctic areas
e.
18
Questions 16 and 17 are based on the preceding diagram of the nitrogen cycle.
16. Match the descriptions to these types of bacteria:
denitrifying
nitrifying
nitrogen-fixing
bacteria that convert nitrate to nitrogen gas
a.
bacteria that convert ammonium to nitrate
b.
bacteria in legume nodules that convert nitrogen gas to ammonium
C.
17. Plants cannot use nitrogen gas. What are two ways in which plants receive a supply of nitrogen for
incorporation into proteins and nucleic acids?
is removed from the atmosphere and changed to
18. When humans produce fertilizers, the gas a.
b.
, which enters the atmosphere. Acid deposition occurs when nitrogen oxides and
in the atmosphere are converted to acids that return to Earth.
19. Place a check beside those events that may be expected because of acid deposition.
dying forests
a.
lower agricultural yields
b.
sterile lakes
c.
corroded marble, metal, and stonework
d.
react with one another in the
and b.
20. Photochemical smog arises when a.
presenceof sunlight. Smog contains the pollutants C.
and d .
21. Place a check beside all those effects that may be expected from the occurrence of smog.
breathing difficulties
a.
damage to plants
b.
thermal inversions
c.
cleaner air than usual
d.
22. Place a check beside the statements that correctly describe the results when producers take up phosphate.
a.
becomes a part of phospholipids
becomes a part of ATP
b.
becomes a part of nucleotides
c.
becomes a part of the atmosphere
d.
23. Indicate whether these statements are true (T) or false (F). Rewrite all false statements as true statements.
Excess phosphate in bodies of water may cause radiation poisoning. Rewrite:
a.
b.
Most ecosystems have plenty of phosphate. Rewrite:
The phosphorus cycle is a sedimentary cycle. Rewrite:
d.
Phosphate enters ecosystems by being taken up by animals. Rewrite:
24. Place a check beside those items that correctly describe biological magnification.
pertains to organic poisons such as pesticides and herbicides
a.
affects other organisms but not humans
b.
refers to an accumulation of foreign molecules in the body because they are not excreted
c.
refers to an enlargement of certain parts of the body due to evolution
d.
25. What is the ozone shield, and why is it important?
419
26. Explain the significance of the following:
Cl +03 C10 + 02
27. What are some of the effects of increased ultraviolet radiation on humans and other organisms?
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420
acid deposition
aquifer
carnivore
CFC
consumer
ecosystem
eutrophication
food chain
food web
nitrification
PAN
An organic compound containing carbon, chlorine, and fluorine atoms.
A rock layer that contains water and releases it in appreciable quantities to wells
or springs.
The order in which one population feeds on another in an ecosystem.
Organism that feeds on another organism in a food chain.
In a food chain, a consumer that eats other animals.
Biological community together with the associated abiotic environment; characterized by the flow of energy and the cycling of inorganic nutrients.
Type of chemical found in photochemical smog.
Process by which nitrogen in ammonia and organic compounds is oxidized to
nitrites and nitrates by soil bacteria.
In ecosystems, complex pattern of interlocking and crisscrossing food chains.
Enrichment of water by inorganic nutrients used by phytoplankton; overenrichment often caused by human activities leading to excessive bacterial
growth and oxygen depletion.
The sulfate or nitrate salts of acids produced by commercial and industrial activities return to Earth as rain or snow.