Question

Nitrogen-fixing bacteria convert atmospheric nitrogen into which product?

• A. ${NO_{3}}^{-}$
• B. $NO_{2}$
• C. Amino acids
• D. $NH_{4}^{+}$

Hint:

Nitrogen fixation is a Reduction process. It starts with $N_2$ and ends with Ammonium ($NH_{4}^{+}$).

Answer 1

The Correct Option is D

Concept: Biological Nitrogen Fixation (BNF) is the process by which specific microorganisms capture atmospheric dinitrogen ($N_2$) and reduce it to a biologically useful form.

Step 1: The Chemical Reaction.
The enzyme nitrogenase catalyzes the breaking of the triple bond in $N_2$. This is a highly energy-intensive reduction process. The general reaction is: \[ N_2 + 8H^+ + 8e^- + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i \]

Step 2: From Ammonia to Ammonium.
In the aqueous environment of the soil or within the plant cell (cytosol), the gaseous ammonia ($NH_3$) produced by the bacteria instantly picks up a hydrogen ion to become the ammonium ion ($NH_{4}^{+}$).

Step 3: Conclusion.
While plants eventually assimilate nitrogen into amino acids (3) or take up nitrates (1), the immediate stable product of the nitrogen fixation process itself is ammonium ($NH_{4}^{+}$).