Question

what do you mean by biological nitrogen fixation

Answer 1

Biological nitrogen fixation (BNF) is the term used for a process in whichnitrogen gas (N2) from the atmosphere is incorporated into the tissue of certain plants. Only a select group of plants is able to obtain N this way, with the help of soil microorganisms.

As ADDITIONAL INFO :

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. The reaction for BNF is:

N2 + 8 H+ + 8 e− → 2 NH3 + H2

The process is coupled to the hydrolysis of 16 equivalents of ATP and is accompanied by the co-formation of one molecule of H2. In free-living diazotrophs, the nitrogenase-generated ammonium is assimilated into glutamatethrough the glutamine synthetase/glutamate synthase pathway.

Enzymes responsible for nitrogenase action are very susceptible to destruction by oxygen. Many bacteria cease production of the enzyme in the presence of oxygen. Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with a protein such as Leghemoglobin