Question

Assertion (A): Nitrogenase enzyme gets inactivated in the presence of oxygen, yet nitrogen fixation occurs in aerobic cells of legume nodules
Reason (R): Leghaemoglobin allows presence of oxygen just sufficient for cellular respiration only

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true and R is not the correct explanation of A
• C. A is true but R is false
• D. Both A and R are false

Answer 1

The correct option is A Both A and R are true and R is the correct explanation of A

Leghaemoglobin is an oxygen carrier protein which is found in the nitrogen-fixing root nodules of a leguminous plant. It is produced by the legumes in respond to roots being colonised by nitrogen-fixing bacteria, Rhizobium, as a part of symbiotic interaction between the plant and the bacteria.

The enzyme, nitrogenase in the nitrogen-fixing bacteria is highly sensitive to oxygen and the enzyme gets inactivated in the presence of oxygen. So, the bacteria need to protect the nitrogenase enzyme from oxygen. Leghaemoglobin pigment which is present in the root nodules scavenges free oxygen so that nitrogenase can carry out its activity of nitrogen fixation unhindered.
Leghaemoglobin allows presence of oxygen just sufficient for cellular respiration to take place.