Describe the various stages of nirogen cycle.

Explanation

The nitrogen cycle consists of following states:
1. Fixation of atmospheric nitrogen : Di - nitrogen molecule from the atmosphere progressively gets reduced by addition of a pair of hydrogen atoms. Triple bond between two nitrogen atoms `(N -= N)` are cleaved to produce ammonia. Nitrogen fixation process requires Nitrogenase enzyme complex, Minerals (Mo, Fe and S), anaerobic condition, ATP, electron and glucose 6 phosphate as `H^+` donor. Nitrogenase enzyme is active only in anaerobic condition. To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen. Nitrogen fixing bacteria in root modules appears pinkish due to the presence of this leghaemoglobin pigment.

Overall equation :
`N_2 + 8e^(-) + 8H^(+) + 16 ATP to 2NH_3^(+) + H_2 + 16 ADP + 16 P i`
2. Nitrification : Ammonia `(NH_3^+)` is converted into Nitrite `(NO_2^-)` by Nitrosomonas bacterium. Nitrite is then converted into Nitrate `(NO_3^-)` by Nitrobacter bacterium. Plants are more adapted to absorb nitrate `(NO_3^-)` than ammonium ions from the soil.
`2NH_3^+ + 3O_2 overset("Nitrosomonas)(rarr) 2NO_(2)^(-) + 2H^(+) + 2H_2O`
`2 NO_(2)^(-) + O_(2) overset("Nitrobacter")(rarr)2NO_(3)^(-)`
3. Nitrate Assimilation: The process by which nitrate is reduced to ammonia is called nitrate assimilation and occurs during nitrogen cycle.
`NO_(3)^(-) underset(Mo)overset("Nitrate reductase")(rarr) NO_(2)^(-)`
4. Ammonification : Decomposition of organic nitrogen (protein and amino acids) from dead plants and animals into ammonia is called ammonification. Organism involved in this process are Bacillus ramosus and Bacillus vulgaris.
5. Denitrification : Nitrates in the soil are converted back into atmospheric nitrogen by a process called denitrification. Bacteria involved in this process are Pseudomonas, Thiobacillus and Bacillus subtilis.
`underset((NO_3^-))("Nitrate") overset("Pseudomonas")(rarr) underset((N_2))("Molecular Nitrogen")`.