NITROGEN AND NITROGEN CYCLE

  WHAT IS NITROGEN?

Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, acids and vitamins. Nitrogen covers up to 78% of the atmosphere of the earth. It is the most plentiful (in a large amount.) gas in the air. When we inhale, we take some amount of nitrogen into our lungs and exhale it. But plants need nitrogen for their survival. They cannot take nitrogen directly from the air. A bacterium, which lives in the soil and roots of some plants, take nitrogen from the air and changes its form so that plants can use it. The name of this bacterium is Rhizobium .

 

  NITROGEN FIXATION 

Rhizobium bacteria are involved in the fixation of nitrogen in leguminous plants (pulses). Recall that Rhizobium lives in the root nodules   of leguminous plants such as beans and peas, with which it has a symbiotic relationship. Sometimes nitrogen gets fixed through the action of lightning. But you know that the amount of nitrogen in the atmosphere remains constant.

NITROGEN CYCLE

The 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 compounds, it can be utilized by plants from the soil through their root system. 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 nitrogenous wastes into nitrogenous compounds to be used by 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.