Question

If radiation inactivates all nitrogenase enzymes, then there will be no _______.
A. Conversion from nitrate to nitrite in legumes
B. Fixation of nitrogen in legumes
C. Fixation of atmospheric nitrogen
D. Conversion from ammonium to nitrate in soil

Answer 1

Hint:
Even though the atmosphere has 78% nitrogen, it is not available directly for consumption. Living organisms such as plants and animals require nitrogen supplies for their daily activities. Nitrogen fixation is the process by which atmospheric nitrogen is converted to ammonia or other nitrogenous compounds.

Complete step by step answer:
 Nitrogenase is the enzyme that is produced by some microorganisms such as Cyanobacteria, Rhizobium, etc. Nitrogenase plays a key role in nitrogen fixation by converting free nitrogen into ammonia. So, if all nitrogenase enzymes are inactivated by radiation, atmospheric nitrogen fixation cannot take place, which will impact entire life forms on the earth.
Nitrate is reduced to nitrite by nitrate reductase in the cytoplasm, and then it is reduced to ammonia reductase in the chloroplasts by nitrite. So nitrogenase enzyme does not play any role in the conversion of nitrate to nitrite. The conversion of ammonium to nitrate in the soil does not require the action of the nitrogenase enzyme. The Rhizobium present in the root nodules of the leguminous plants directly traps the nitrogen for the plants and is not affected by the radiation since they don’t require nitrogenase.

Option ‘C’ is correct

Note:
Lightning can also help in nitrogen fixation. It is a natural process where the energy of lightning breaks and converts the non-absorbable form of nitrogen into a usable form.