Question

Find the correct order for the conversion of organic form of nitrogen into inorganic form by soil microorganisms.
A. Formation of nitrites
B. Formation of ammonia
C. Formation of free nitrogen
D. Formation of nitrates
Choose the correct answer from the options given below:

• A. B, C, D, A
• B. C, D, A, B
• C. D, A, B, C
• D. B, A, D, C

Hint:

The Nitrogen flow is: Ammonia ($NH_3$) $\rightarrow$ Nitrite ($NO_2^-$) $\rightarrow$ Nitrate ($NO_3^-$) $\rightarrow$ Free Nitrogen ($N_2$).

Answer 1

The Correct Option is D

Concept: The conversion of organic nitrogen (from dead matter) into inorganic forms is a sequence of oxidation steps within the nitrogen cycle.

Step 1: Ammonification.
The first step in breaking down organic matter (like proteins) is the Formation of ammonia (B). This process is carried out by saprophytic "ammonifying" bacteria.

Step 2: The First Nitrification Step.
Next, the ammonia is oxidized. The first product is the Formation of nitrites (A), typically performed by bacteria like Nitrosomonas.

Step 3: The Second Nitrification Step.
The nitrites are then quickly oxidized into the most stable inorganic form for plant use: the Formation of nitrates (D), performed by bacteria like Nitrobacter.

Step 4: The Final "Reset".
To complete the cycle, inorganic nitrogen is eventually returned to the atmosphere through the Formation of free nitrogen ($N_2$) (C) during denitrification. Note: While (4) provides the sequence B-A-D-C, it follows the logical path from organic breakdown to the final gaseous state.