Bio Review Notes #59
ECOSYSTEMS
Performance Objectives:
An ecosystem includes both a community and the physical environment that supports it. The largest ecosystem of all, the biosphere, includes the Earth and all its inhabitants.

 Physical environments: Environments differ in temperature, humidity, rainfall (and their seasonal variations), and other physical factors such as elevation, slope, soil type, and water salinity.

Adaptations to extreme environments: Species that adapt to harsh environments enjoy freedom from competition with other species that cannot cope with the environmental stress.
  • Adaptations to cold may include insulation, reduced surface area, leaf loss, etc.
  • Adaptations to desert conditions (extreme heat & dryness) may include burrowing, daytime inactivity, or thick, waxy cuticles.
Nutrients cycle through ecosystems:

Carbon cycle: Autotrophs (mostly green plants) fix CO2 into organic compounds, which then pass up the food chain. Decomposer organisms (called saprobes or saprophytes) feed on dead or decaying organic matter (corpses, feces, fallen leaves, etc.). All organisms return CO2 to the air and other carbon compounds to the soil and water.

Oxygen cycle: All organisms (except anaerobic bacteria and archaea) use oxygen in their respiration and release CO2 and water. Photosynthetic plants split water molecules and release oxygen to the atmosphere.

Nitrogen cycle:   Nitrogen-fixing bacteria convert atmospheric N2 into soluble nitrogen compounds, which plants absorb. Nitrogen compounds (including proteins) pass up the food chain. Animals excrete urea and other nitrogen wastes. Saprobes digest proteins into simpler compounds. Nitrifying bacteria convert ammonium salts and urea into nitrites, then into nitrates. Denitrifying bacteria convert nitrates to N2 gas.

Human impacts:
  • Pollution results from problems of waste disposal.
  • Acid rain results from burning sulfur (an impurity in coal) and from nitrogen oxides.
  • Destruction of tropical forests and burning of fossil fuels cause a global CO2 increase, causing a greenhouse effect that leads to global warming.
  • Ozone depletion from certain photoactive chemicals reaching the upper atmosphere allows more ultraviolet (UV) radiation to reach ground level, raising mutation rates and cancer risks.
  • Endangered species risk extinction, mostly from habitat destruction.
  • Overpopulation can worsen all the above problems.

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