Describe the Nitrogen Cycle.

(N/A) $\Rightarrow$ Apart from carbon,hydrogen,and oxygen,nitrogen is the most prevalent element in living organisms.
$\Rightarrow$ Nitrogen is a constituent of amino acids,proteins,hormones,chlorophylls,and many vitamins.
$\Rightarrow$ Plants compete with microbes for the limited nitrogen available in the soil.
$\Rightarrow$ Thus,nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
$\Rightarrow$ Nitrogen exists as two nitrogen atoms joined by a very strong triple covalent bond $(N \equiv N)$.
$\Rightarrow$ The process of conversion of nitrogen $(N_2)$ to ammonia is termed as nitrogen fixation.
$\Rightarrow$ In nature,lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides $(NO, NO_2, N_2O)$. Industrial combustions,forest fires,automobile exhausts,and power-generating stations are also sources of atmospheric nitrogen oxides.
$\Rightarrow$ Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
$\Rightarrow$ Some of this ammonia volatilises and re-enters the atmosphere.
$\Rightarrow$ Most of it is converted into nitrate by soil bacteria in the following steps:
$\Rightarrow$ Ammonia is first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococcus.
$\Rightarrow$ The nitrite is further oxidised to nitrate with the help of the bacterium Nitrobacter.
$\Rightarrow$ These steps are called nitrification.
$\Rightarrow$ Ammonia $\xrightarrow{\text{Oxidation}}$ Nitrite
$\Rightarrow$ Nitrite $\xrightarrow[\text{Oxidation}]{\text{Nitrobacter}}$ Nitrate
$\Rightarrow$ These nitrifying bacteria are chemoautotrophs.
$\Rightarrow$ The nitrate thus formed is absorbed by plants and transported to the leaves.
$\Rightarrow$ In leaves,it is reduced to form ammonia.
$\Rightarrow$ Nitrate $\rightarrow$ leaves $\xrightarrow{\text{Reduction}}$ Ammonia $\rightarrow$ Amino acid
$\Rightarrow$ It finally forms the amine group of amino acids. Nitrate present in the soil is also reduced to nitrogen by the process of denitrification.
$\Rightarrow$ Nitrate $\xrightarrow{\text{Denitrification}}$ Nitrogen
$\Rightarrow$ This process is carried out by bacteria like Pseudomonas and Thiobacillus.