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 30 (p. 624)

1. The development of reliable agriculture fostered the rapid growth in human populations. This event fostered development of permanent settlements and cities. The major cultural event that eventually took place was the specialization of professions.

2. Every habitat, large or small, has its carrying capacity. Our planet is no exception. The depletion of resources by the developed world may be a greater threat than the increase of population in the undeveloped world.

3. Rice, wheat, and corn supply more than half of the human energy requirements. Just over 100 species of plants supply over 90% of all calories consumed.

4. The chief drawbacks are: (1) it is not cheap, when the costs of plant construction are included. (2) Nuclear safety is not guaranteed with current reactor design, and what if a nuclear-powered country like France were attacked with conventional weapons in a war? (3) Spread of nuclear weapons material and technology will create a more dangerous world. 4) Nuclear waste disposal problems have not been solved, nor has a single nuclear power plant yet been decommissioned successfully.

5. Chlorinated hydrocarbons were banned in the United States due to their deleterious effects (such as thinned eggshells in birds), as well as their tendency to "bioaccumulate," or accumulate in the tissue of organisms that consumed contaminated material. Foreign imports may still contain traces of these contaminants, however, which is how they can get back into the country.

6. Acid precipitation forms when the sulfur compounds (SO₂ and other sulfates) from industrial pollution combine with water vapor in the air to form an acid, which subsequently precipitates back to earth. It is difficult to regulate because acid precipitation theoretically "generated" in one country can actually fall to Earth in another.

7. Ozone is O₃ and is formed as light stimulates the dissociation of O₂ by ultraviolet radiation. Decreasing the earth's ozone layer results in an increased rate of human skin cancers and damage to the ocean's phytoplankton and other photosynthetic organisms. The primary cause is probably manufactured chemicals, especially chlorofluorocarbons. High levels of ozone are also deleterious because they lead to damage to human lungs and to citrus plants.

8. Individuals can do many things personally to conserve resources and prevent waste and pollution. However, to make a significant change in the world one must become an activist and try to influence the "powers that be."