Briefly describe the mechanism of biological nitrogen fixation

Briefly describe the mechanism of biological nitrogen fixation.
What is on meant by biological nitrogen fixation ? Elaborate your answer with the example
Explain symbiotic nitrogen fixation in leguminous plants.

Biological nitrogen fixation is the process in which certain living organisms convert the free nitrogen into those compounds which can be used by plants.
(a) The organisms may be free-living bacteria (e.g., Azotobacter), symbiotic bacteria like Rhizobium or Cyanobacteria.
(b) The enzyme involved in the process is nitrogenase,
which is a Mo-Fe protein.
© During this process, the atmospheric nitrogen is reduced by the addition of hydrogen.
(d) The three bonds between the two nitrogen atoms (N = N) are broken and hydrogen is progressively added to from ammonia.
(e) This fixation requires three components :
(i) ATP, to supply energy.
(ii) A strong reducing agent, to transfer hydrogen atoms.
(iii) The enzyme system (nitrogenase)
(g) The overall reaction is as follows :