Natural Resources — Science STD 9 — Question

Nitrogen exists as free nitrogen in the atmosphere. This free nitrogen is fixed into compounds of ammonia and nitrates. Most of the organisms cannot utilise nitrogen as molecular nitrogen. Plants take compounds containing nitrogen from the soil. From plants nitrogen passes into the food web. Decay of dead plants, animals and excreta causes return of nitrogen compounds to the soil. Denitrifying bacteria cause liberation of free nitrogen in the atmosphere.