Assertion : Nitrogenase enzyme gets inactivated in presence of oxygen yet `N_(2)` fixation occurs in aerobic cells of legume nodules.
Reason : Leghaemoglobin allows presence of oxygen just sufficient for cellular respiration only.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Answer

A

Explanation

Nitrogenase enzyme is the enzyme responsible for nitrogen fixation in leguminous plants inside nodules infected by Rhizobia. This enzyme undergoes irreversibledamage in presence of oxygen and `N_(2)` fixation is stopped but the eukaryotic cells of nodules respire aerobically thus, oxygen is needed. Proper balance of oxygen amount is maintained by oxygen scavanger protein called leghaemoglobin which maintains oxygen level just sufficient for cellular respiration so the cells do not die and it remove extra oxygen to produce anaerobic atmosphere for proper functioning of nitrogenase enzyme.