Nitrogen gas makes up to 78% of the atmosphere and
it is also a part of many molecules essential to life, like
proteins, nucleic acids ( DNA and RNA ) and some
Nitrogen is also found in other biological compounds
such as alkaloids.
Nitrogen is an essential nutrient for all life forms.
All organisms cannot use the atmospheric nitrogen
However some bacteria and blue green algae are
able to do so.
They convert nitrogen molecules into simpler
forms such as nitrates and nitrites.
Nitrogen fixing bacteria like rhizobium, are found
in the roots of some of the dicot plants such as
These are present in special structures called root
Nitrogen fixation also takes place during lightening.At the time of lightening high temperature and pressure
created in the air converts nitrogen into oxides of nitrogen.
These oxides dissolve in rain water to form nitric and nitrous
This process is know as atmospheric nitrogen fixation.
These acids are then utilized by various life forms
Nitrogen from the atmosphere
4 000 000 000 Gt
Human beings also fix nitrogen for their use.
This is done by manufacturing ammonia and urea
in the industries.
This is called as the industrial nitrogen fixation.
Plants take up nitrites and nitrates and converts
them into amino acids. Which are used to make
These proteins are consumed by animals.
Thus we can say that nitrogen is present in both
plants and animals.
Nitrogen is returned back to the nature when an
animal excretes or when an animal dies.
Some other bacteria present in the soil converts the
various compounds of nitrogen back into nitrates
A different type of bacteria converts the nitrates and
nitrites into elemental nitrogen. ( nitrogen in the
The process of conversion of nitrates and nitrites into
ammonia is called ammonification.
Conversion of ammonia into nitrites and then nitrates is
Thus, there is a nitrogen-cycle in nature
in which nitrogen passes from its
elemental form in the atmosphere into
simple molecules in the soil and
water, which get converted to more
complex molecules in living beings and
back again to the simple nitrogen
molecule in the atmosphere.