Question

Leguminous plants are able to fix atmospheric nitrogen through the process of symbiont nitrogen fixation. Which one of the following statements is not correct about this process?

• A. Leghaemoglobin scavenges oxygen and is pinkish in colour
• B. Nodules act as sites for nitrogen fixation
• C. The enzymes, nitrogenase catalyses conversion of atmospheric $N_2$ to $N{H}_3$
• D. Nitrogenase is insensitive to oxygen

Answer 1

The correct option is D Nitrogenase is insensitive to oxygen

Plants do not directly absorb atmospheric nitrogen. In nature, a nitrogen cycle is operational, which continuously shuttles nitrogen between the living and non-living components of the ecosystem.

Nitrogen fixation is the process of converting inert atmospheric nitrogen into utilisable compounds, like nitrate and ammonia.

Rhizobium is symbiotic nitrogen fixer found in the root nodules of legume plants. It contains the enzyme nitrogenase, which carries out the process of nitrogen fixation using reduced substrates from the host plant.

The enzyme nitrogenase is highly sensitive to free oxygen and hence, root nodules carry the reddish (or pinkish) pigment leghemoglobin, which binds free oxygen and thus protects nitrogenase.

So, the correct answer is option D.