The Nitrogen Cycle The atmosphere holds the greatest reservoir of nitrogen, but, as gaseous, triple-bonded N 2 , it is chemically inert and unusable by plants and almost all other organisms. A few kinds of bacteria that possess the enzyme nitrogenase are the exceptions. They are able to convert (reduce) N 2 to ammonium ions (NH 4 + ), which many organisms, including plants, are able to metabolize. The process is called nitrogen fixation and ranks equally with photosynthesis in significance to life. When organisms die, decay bacteria and fungi release the fixed N of organic compounds. New organisms then reformulate it into amino acids—hence proteins—together with nucleic acids, nucleotides, coenzymes, and vitamins all of which are essential to life. The denitrifying bacteria return some nitrogen to the atmosphere as N 2 . This process— denitrification
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This note was uploaded on 11/14/2011 for the course BIO 1421 taught by Professor Farr during the Fall '08 term at Texas State.