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 28 (p. 590)

1. Chemicals are generally stored in the atmosphere, water, and rocks in these cycles. There is much more of the life-sustaining chemicals in these reservoirs than in organisms.

2. Denitrification is the conversion of nitrate to nitrogen gas and nitrous oxide. The process is carried out by several different genera of bacteria.

3. The reservoir of phosphorus exists in mineral form rather than in the atmosphere, as in the other cycles. The natural sources for phosphorus are soil (small amounts), isolated rock outcroppings, ocean sediments, guano, and bone meal.

4. Deforestation produces fewer plants, which results in greater water runoff and increased land damage due to flooding. With regard to overall fertility of the land, with increased water runoff, greater amounts of nutrients are lost from the immediate environment and fertility is decreased.

5. Predation in upper trophic levels reduces consumption of the lower levels. The lower level organisms will increase but will also compete more for resources. An increase of nutrients for the lower trophic levels will increase the food supply for the higher levels.

6. Primary productivity is the amount of organic matter produced from solar energy in a given area during a given period of time. Gross primary productivity is the total organic matter produced (even that consumed by photosynthesis). Net primary productivity is the amount of organic material produced in a community in a given period of time that is available to the heterotrophs.

7. Herbivorous diets provide the greatest food value to living organisms because they involve eating the primary producer on the first trophic level rather than a primary or secondary consumer, which is a higher trophic level; therefore less energy is lost going from one trophic level to the next.

8. Tropical rain forests have high levels of species diversity because of constant conditions, spatial heterogeneity, and high levels of predation.

9. Distant islands tend to have lower species diversity because of less opportunity for colonization. Different sized islands have different species numbers because of different diversity and abundance of habitats and food.