It can be found in plants by herbivores or in other animals by carnivores. However, most processes using nitrogen employed by living organisms require nitrogen to be altered to a different state. There are four processes which take place during the nitrogen cycle in which living organisms make use of this important element. Fixation is the conversion of N 2 into either ammonia by biological fixation, or to nitrates by lightning and other inorganic processes. Ninety percent of the earth's fixed nitrogen is produced by biological fixation each year.
Fixation requires energy and is summed up by the following two chemical equations.
2 NH 3 These chemical processes are performed by mutualistic bacteria that generally live on the roots of plants, as well as cyanobacteria and some free living bacteria. These amino acids are then oxidized to form water, carbon dioxide, and ammonia. The ammonia plays an important role in the ecosystem, including being absorbed into plant roots, and passing through the food chain. Nitrification involves the oxidation of ammonia into nitrate and nitrite, giving off energy. Two types of bacteria, nitrosomonas and nitrobacters, use nitrates and nitrites respectively as energy sources.