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Briefly describe the mechanism of biological nitrogen fixation. 


What is meant by biological nitrogen fixation ? Elaborate your answer with the example 


Explain symbiotic nitrogen fixation in leguminous plants.

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Biological nitrogen fixation is the process in which certain living organisms convert the free nitrogen into those compounds which can be used by plants. 

(i) The organisms may be free-living bacteria (e.g., Azotobacter), symbiotic bacteria like Rhizobium or Cyanobacteria. 

(ii) The enzyme involved in the process is nitrogenase, which is a Mo-Fe protein. 

(iii) During this process, the atmospheric nitrogen is reduced by the addition of hydrogen. 

(iv) The three bonds between the two nitrogen atoms (N ≡ N) are broken and hydrogen is progressively added to form ammonia. 

(v) This fixation requires three components: 

(a) ATP, to supply energy. 

(b) A strong reducing agent, to transfer hydrogen atoms. 

(c) The enzyme system (nitrogenase) 

(vi) The overall reaction is as follows : 

N2 + 8e- + 8H+ + 16 ATP-→ 2NH3 + H2 + 16 ADP +16 Pi

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