Question

How does the nitrogen fixation occur in the legumes?
(A) By specialized bacteria in their roots
(B) By specialized bacteria in their leaves
(C) Independent of the bacteria that live in them
(D) Not by any of the above methods

Answer 1

Hint: Some of the microorganisms have nitrogen fixation genes in them to store the nitrogen from the atmosphere in the roots of the leguminous plants. And this nitrogen is used by the plants for its growth. In turn, they get the nutrients from the plants.

Complete Answer:
- These microorganisms are found on the roots of the plants. These are found only in the plants which are leguminous in nature.
- These plants have bulge-like structures in their roots and these structures are called nodules. The bacteria like rhizobium fix the atmospheric nitrogen in these plants’ nodules. This nitrogen is converted into the ammonia and is used by the plants for its growth and development.
- This nitrogen fixing is the ability that comes from the ‘Nif’ gene in their nucleic acid. The plasmid of the rhizobium has the ‘Nif’ gene in it. The plant in turn provides shelter for the rhizobium bacteria for its growth.
- Thus, these two organisms are in a symbiotic relationship with each other. These are known as symbionts. Thus, the nitrogen fixation occurs in legumes by the specialized bacteria in their roots.

Thus, the option (A) is correct.

Note: These rhizobia have the enormous values in the field of agriculture. This is because they fix most of the atmospheric nitrogen in the soil. Hence this is used as the bio fertilizer which increases the yield of the agricultural crops and reduces the use of artificial fertilizer.