Nitrogen is an important component of amino acids, proteins and nucleic acids which form structural and functional constituents of cell protoplasm. Air contains about 78% of nitrogen, which exists in molecular form as N2. Water bodies also contain nitrogen. Producers cannot absorb nitrogen in its elemental form. It has to be first converted into nitrates for the use of plants. The process of converting atmospheric nitrogen into nitrates is called nitrogen fixation. The atmospheric nitrogen after nitrogen fixation gets converted into nitrates, which is then absorbed by plants and assimilated into their system. Organic compounds like proteins are formed which are decomposed to ammonia and amino acids by decomposers in the soil.