Describe nitrogen cycle. 

Explanation

Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as a part of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen. Once nitrogen is converted into these usable forms, it can be utilised by plants through their root system. This is the process of .fixing. of nitrogen. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds.
  When plants and animals die, bacteria and fungi present in the soil convert the various nitrogenous wastes into nitrogenous compounds. Certain other bacteria convert some parts of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant.