Nitrogenase in bacteria is oxygen-sensitive. Which bacterial adaptation favours nitrogen fixation?

Correct answer: (c) Elevated respiration rate

Explanation

Nitrogenase, the enzyme that fixes atmospheric nitrogen into ammonia, is quickly destroyed by oxygen. Aerobic nitrogen-fixing bacteria, such as *Azotobacter*, need oxygen for energy but must keep it away from nitrogenase.

They solve this with a very high rate of respiration (respiratory protection): they use up oxygen so fast that the inside of the cell, around the nitrogenase, stays almost free of oxygen.

Other ways: cyanobacteria fix nitrogen in thick-walled heterocysts, and legume root nodules use leghaemoglobin to bind oxygen. Aerobic photosynthesis would add oxygen, not remove it.