Nitrogen is the most prevalent element in living organism.
❑ It is the constituent of amino acids, proteins, hormones and many of the vitamins.
❑ Nitrogen cycle will simply deal with the circulation of nitrogen between various environmental component such as soil, atmosphere and organism
❑ The steps of nitrogen cycle
1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification
The process of conversion of nitrogen (N2 or N=N) to ammonia is termed as nitrogen fixation ❑ Nitrogen fixation is of three types
Atmospheric N2 Fixation
Lightning and UV radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O)
Industrial N2 Fixation
Industrial combustions, forest fires, automobile exhausts and power generating stations are also sources of atmospheric nitrogen oxides.
Biological
Fixation
The conversion of N2 to ammonia with help of living organisms such as bacteria and blue green algae.
Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification. ❑
Some soil bacteria used in this process are called ammonifying bacteria.
❑ Anaerobic breakdown is called putrefaction while aerobic breakdown is called decay. ❑ E.g. Bacillus vulgaris, Bacillus ramosus, Bacillus mycoides.
Some of the ammonia formed via ammonification volatilizes and re-enters the atmosphere
Oxidation of ammonia into nitrates by nitrifying bacteria is called nitrification.
During this process energy is released with the help of which, bacteria synthesise their own food so they are called chemoautotrophs.
Steps of Nitrification Reaction
Nitrosomonas
Nitritation:
Nitrobacter
Nitration:
Plants absorb the nitrate ands is transported to the leaves. In leaves, it is reduced to form ammonia that finally forms the amine group of amino acids
Nitrate present in the soil is also reduced to nitrogen by the process of denitrification.
Denitrification is carried by bacteria
Pseudomonas and Thiobacillus.
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