Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 29 (p. 610)

1. Faced with a range of temperatures during the year, animals may manufacture a circulatory or cellular antifreeze, change thickness or color of fur, hibernate in the cold weather, or burrow into the mud to escape heat. Breeding seasons may be altered to adjust to seasons. Plants may shed leaves or become dormant.

2. Most deserts are located at these latitudes because the air is falling and being warmed; since warm air holds more moisture than cool air, there is less precipitation. It is more likely that a desert will form at the interior of a continent due to the distance from the sea.

3. A biome is an assemblage of organisms that has a characteristic appearance and that occurs over a wide terrestrial geographical area. The two key physical factors that affect the distribution of biomes across the earth are (1) amounts of heat that reach the earth and its seasonal variation and (2) global atmospheric patterns and resulting oceanic circulation patterns.

4. Plankton are microscopic organisms, algae, and cyanobacteria. Nekton are fish and other larger organisms that feed on the nekton. The photosynthetic plankton are important because 40% or more of the earth's photosynthesis occurs in them. The level is slow and there is a rapid turnover of nutrients in the surface zone; most of the nutrients are tied up in the organisms.

5. The abyssal zone would appear to be quite inhospitable, with its intense pressure, low temperature, and complete lack of light (and therefore photosynthesis). Sulfur-spewing hydrothermal vents provide chemoautotrophs with a metabolite (sulfur), and therefore can support a surprisingly diverse community around the vents, including tube worms that can reach over a meter in length, large clams, acorn worms, and a host of other unusual organisms.

6. There is surprising diversity in the abyssal zone. The base of the abyssal ecosystem is chemosynthesis by sulfur bacteria.

7. Eutrophic lakes have high productivity whereas oligotrophic lakes have little productivity. Note that productivity refers to biomass, which is often mostly comprised of weeds. Humans contribute to eutrophication of lakes through pollution, especially fertilizer runoff.