Answer:
The
various steps of nitrogen cycle are as follows:
(i) Nitrogen fixation: It is the conversion of atmospheric nitrogen into water-soluble
compounds like nitrates and nitrites either by the free-living bacteria or Rhizobium
that are found in the root nodules of legumes.
Atmospheric nitrogen also gets converted into nitrates and
nitrites naturally by lightning.
(ii) Ammonification: Death and decay of plant bodies
release ammonia into the atmosphere. Animals also give out ammonia along with
urea and uric acid as excretory products. These nitrogenous compounds are
converted to ammonia by putrefying bacteria and the process is known as
ammonification.
(iii) Nitrification: Ammonia is then converted first into
nitrites and then into nitrates by the nitrifying bacteria, the process being
called as nitrification.
Plants generally take up nitrates and nitrites and convert
them into amino acids.
(iv) Denitrification: When the animal or the plant dies,
denitrifying bacteria in the soil convert the various compounds of nitrogen
back into nitrates and nitrites. The nitrates and nitrites are converted into
elemental nitrogen by Pseudomonas. This process is called denitrification.
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