1. Biogeochemical cycles are geological cycles that involve the biologically controlled cycling of chemicals. 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. Over 90% of fresh water in the Earth is in underground aquifers. Water in these systems both moves and is replenished very slowly, making pollution of this water a serious problem that would be difficult, if at all possible, to correct.
3. The earth holds nitrogen as atmospheric nitrogen gas, fixed nitrogen in the soil, and nitrogenous compounds in organisms. The process of fixation involves converting nitrogen gas to ammonia and is performed by bacteria, especially those associated with legumes, and certain cyanobacteria.
4. Denitrification is the conversion of nitrate to nitrogen gas and nitrous oxide. The process is carried out by several different genera of bacteria, and serves an important role, because without it occurring, all nitrogen would become fixed and ultimately washed out to sea, unavailable for use by the different ecosystems.
5. 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.
6. Deforestation produces fewer plants, which results in greater water runoff and increased land damage due to flooding. With regard to the nutrient cycles and overall fertility of the land, with increased water runoff, greater amounts of nutrients are lost from the immediate environment and fertility is decreased.
7. 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.
8. The wave-battered intertidal zone is the most productive biological community. Tropical rain forests are more productive than temperate forests, which are more productive than the desert.
9. On the average, 10% of the energy is transferred from one trophic level to the next. 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. The more efficient method would be to feed them corn.
10. Three factors have produced this altered concept: (1) climate is continually changing; (2) succession is a slow process; and (3) the nature a region's vegetation is greatly affected by human activities. The organisms often associated with early stages of succession are those that exhibit symbiotic relationships: lichens = algae + fungi; legumes = plant + bacteria; and mycorrhizae = plant + fungi.
11. Biomass and productivity are related to the successional age of an ecosystem in that older ecosystems have greater biomass, but lower net productivity. There are more species in mature ecosystems, and especially many more heterotrophic species in mature ecosystems. This results because mature ecosystems better regulate their nutrient cycles and generally have more specialized organisms.