Nitrogen is a gaseous, non-metallic chemical element made of
seven protons and seven electrons, made up about 78% of the earth’s atmosphere. Nitrogen, a component of proteins and nucleic
essential to life on Earth.
The nitrogen cycle is the biochemical process by which
nitrogen moves through the environment. It is important in maintaining the
balance of nitrogen in water, soil and atmosphere.
Living organisms cannot
pick up elemental gaseous nitrogen directly from the atmosphere.
It is carried out by
nitrogen-fixing bacteria and blue-green algae.
(Nostoc sp. and Rhizobium sp.) can assimilate atmospheric nitrogen into
ammonium compounds (NH3, NH4+).
Thunderstorms and lightning
convert oxygen and nitrogen to nitrogen oxide.
This gas involves in
raindrops to form nitric acid which combines with the minerals in the soil to
form nitrates and nitrites.
? Nitrogen oxide ? Nitrites ? Nitrates
Plants consume the nitrates through
their roots to make nucleotides and amino acids.
Animals eat the plants and able to
use these amino acids and nucleic acids in their own cells.
? Ammonia ? Amino Acid + Nucleic acid
The decomposers (ammonifying
bacteria or putrefying bacteria) break down the protein in dead plants and
animals into ammonium compounds (NH3, NH4+).
Common ammonifying bacteria
are Bascillus vulgaris and Bacillus mycoides.
? Amino acid ? Ammonia
It is the process in
which ammonium compounds are oxidized to nitrites and nitrates by nitrifying
Ammonia is oxidised into
nitrites (NO2-) by Nitrosomonas sp.
Nitrites are oxidised
into nitrates (NO3-) by Nitrobacter sp.
The nitrates formed are
absorbed by plants for growth.
? Nitrites ? Nitrates
The process which convert
nitrates to gaseous nitrogen.
The oxygen is used by the
denitrifying bacteria while the nitrogen is returned to the atmosphere.
? Nitrogen + Oxygen