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Chapter 20

25 February, 2016 - 11:05
  1. Figure 20.16 C: Nitrification by bacteria converts nitrates (NO3^-) to nitrites (NO3^-).
  2. Figure 20.29 B. The photic zone, the intertidal zone, the neritic zone, and the oceanic zone.
  3. B
  4. D
  5. B
  6. D
  7. B
  8. D
  9. C
  10. B
  11. D
  12. B
  13. Grazing food webs have a producer at their base, which is either a plant for terrestrial ecosystems or a phytoplankton for aquatic ecosystems. The producers pass their energy to the various trophic levels of consumers. At the base of detrital food webs are the decomposers, which pass their energy to a variety of other consumers. Detrital food webs are important for the health of many grazing food webs because they eliminate dead and decaying organic material, thus clearing space for new organisms and removing potential causes of disease.
  14. Most of the water on Earth is salt water, which humans cannot drink unless the salt is removed. Some fresh water is locked in glaciers and polar ice caps, or is present in the atmosphere. The earth’s water supplies are threatened by pollution and exhaustion. The effort to supply fresh drinking water to the planet’s ever-expanding human population is seen as a major challenge in this century.
  15. Fire is less common in desert biomes than in temperate grasslands because deserts have low net primary productivity, thus very little plant biomass to fuel a fire.
  16. Both the subtropical desert and the Arctic tundra have a low supply of water. In the desert, this is due to extremely low precipitation, and in the Arctic tundra, much of the water is unavailable to plants because it is frozen. Both the subtropical desert and the Arctic tundra have low net primary productivity.
  17. Organisms living in the intertidal zone must tolerate periodic exposure to air and sunlight and must be able to be periodically dry. They also must be able to endure the pounding waves; for this reason, some shoreline organisms have hard exoskeletons that provide protection while also reducing the likelihood of drying out.