Micro Organism of Class 8
Our atmosphere contains about 78% of nitrogen which exists in molecular form as N2. Nitrogen is one of the essential constituents of all living organisms as it is an important component of proteins, chlorophyll, nucleic acids and vitamins. The atmospheric nitrogen cannot be taken directly by plants and animals. It has to be converted into compounds of nitrogen (like nitrates). Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere.
Rhizobium (a bacterium) lives is symbiotic relationship in the root nodules of leguminous plants (beans, peas, etc). It is also involved in the fixation of nitrogen. Sometimes nitrogen also gets fixed through the action of lightning.
Once nitrogen is fixed or converted into the useable compounds, the plants utilize it from the soil through their root system. This is how nitrogen is utilized by plants for the synthesis of different biomolecules. Animals feeding on plants get the nitrogenous compounds. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by the plants again. Certain other bacteria convert some part 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.