ecosystems 1. energy flow 2. chemical...
TRANSCRIPT
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Ecosystems
1. Energy Flow
2. Chemical cycles
water, carbon, nitrogen
3. Human effects on cycles
eutrophication, acid rain
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Ecosystem = community plus abiotic factors
- Conditions (temp, light) Resources (water, nutrients)
• Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat
• Chemicals are recycled between air, water, soil, and organisms
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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• A terrarium ecosystem / Biosphere II
Figure 36.8
Chemical cycling (C, N, etc.)
Light energy
Chemical energy
Heat energy
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–Water cycle
- Carbon cycle
–Nitrogen cycle
Chemicals are recycled between organic matter and abiotic reservoirs
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Figure 36.14
Solar heat
Precipitation over the sea (283)
Net movement of water vapor by wind (36)
Flow of water from land to sea (36)
Water vapor over the sea
Oceans
Evaporation from the sea (319)
Evaporation and transpiration (59)
Water vapor over the land
Precipitation over the land (95)
Surface water and groundwater
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oceans
salt water = 97.5%
freshwater = 2.5%
ice caps
and
glaciers
1.97%
ground-
water
0.5%
lakes,
rivers,
and soil
0.03%
atmosphere
0.001%
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• Carbon is taken from the atmosphere by photosynthesis
–used to make organic molecules
returned to the atmosphere by cellular respiration, decomposers
Carbon cycle
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Figure
36.15
CO2 in atmosphere
Cellular respiration
Higher-level consumers
Primary consumers
Plants, algae,
cyanobacteria
Photosynthesis
Wood and fossil fuels
Detritivores (soil microbes
and others) Detritus
Decomposition
Burning
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• Nitrogen is plentiful in the atmosphere as N2
–But plants and animals cannot use N2
• Some bacteria in soil and legume root nodules convert N2 to compounds that plants can use:
ammonium (NH4+) and nitrate (NO3
–)
The nitrogen cycle relies heavily on bacteria
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• Legumes and certain other plants have nodules in their roots that contain nitrogen-fixing bacteria
Legumes and certain other plants house nitrogen-fixing bacteria
Figure 32.14A
Shoot
Nodules
Roots
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Figure 32.13
ATMOSPHERE
N2
N2 Nitrogen-fixing bacteria
Ammonifying bacteria
Organic material
NH4+
(ammonium) Nitrifying bacteria
NO3–
(nitrate)
Root
NH4+
Amino acids
Soil
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Nitrogen (N2) in atmosphere
Amino acids and proteins in
plants and animals Assimilation by plants
Denitrifying bacteria
Nitrates (NO3
–)
Nitrifying bacteria
Detritus
Detritivores
Decomposition
Ammonium (NH4+)
Nitrogen fixation
Nitrogen-fixing bacteria in soil
Nitrogen-fixing bacteria in root
nodules of legumes
Nitrogen fixation
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76%
naturally
occurring
24%
naturally
occurring
24%
human-
caused
58%
human-
caused
46%
available
54%
used
Atmospheric
CO2
concentration
Terrestrial
nitrogen
fixation
Accessible
surface
water
Human impact on chemical cycles
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• Environmental changes caused by humans can unbalance nutrient cycling over the long term
–Example: acid rain
–Sulfur dioxide, nitrogen oxides create strong acids when dissolved in rain water.
–Low pH kills aquatic life, leaches nutrients from soil
–Calcium deficiency affects everything in food chain: plants, insects, birds. Weak egg shells.
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eutrophication • Algal bloom can cause a lake
to lose its species diversity
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–Human-caused eutrophication wiped out fisheries in Lake Erie in the 1950s and 1960s
Figure 36.19B
– classic experiments on eutrophication led to the ban on phosphates in detergents
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What are the limits to human alteration of chemical cycles and habitats?
• What should the limits be?
• How do we set priorities for what we value in the natural world? Aesthetic, economic, conservation, humans