SHW - Pg. 14

17. ID the role of each of the following in the nitrogen cycle:
a. Nitrogen fixation: The assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous compounds that can be directly used by plants.
b. Ammonification: The decomposition of organic nitrogen back to Ammonium.
c. Nitrification: Oxidation of ammonium to nitrite and then to nitrate.
d. Denitrification: Process which converts Nitrate converted to Nitrite, which returns to the atmosphere.
e. Assimilation: The process of transferring the nitrates from the ground to plants.

18. Why is human population growth at the root of environmental issues?
- Humans introduce many toxic chemicals into ecosystems. Human activities may be causing climate change by increasing atmospheric carbon dioxide

19. Define eutrophication. Why is it a problem?
- Eutrophication is the addition of a substance which will nurture a population. This is a problem because as the nutrients are extracted from the lake, the population will become less diverse and will not grow to natural state.

20. What is the source of acid rain?
- Humans introduce many toxic chemicals into ecosystems. Combustion of fossil fuels is the main cause of acid precipitation.

21. Why is acid rain a problem?
- Toxic chemicals are ingested and metabolized by organisms and can accumulate in the fatty tissues of animals. These toxins become more concentrated in successive trophic levels of a food web, a process called biological magnification. Many toxins cannot be degraded by microbes and persist in the environment for years or decades.