Question

The process of formation of nitrate from ammonia is known as:

• A. Nitrate assimilation
• B. Nitrification
• C. Ammonia assimilation
• D. Denitrification

Hint:

Nitrification plays a critical role in the nitrogen cycle by converting ammonia into a form that plants can use for growth.

Answer 1

The Correct Option is B

The nitrogen cycle has several named steps, each moving nitrogen in a specific direction, so pinning down the direction "ammonia to nitrate" narrows this immediately.
Nitrate assimilation and ammonia assimilation both describe nitrogen being absorbed into organic molecules, not oxidised into nitrate.
Denitrification runs in the opposite direction, converting nitrate back into nitrogen gas.
Nitrification is the specific term for bacteria oxidising ammonia through nitrite and on to nitrate, matching the process described here exactly.
So the correct answer is Nitrification.

Answer 2

Each step of the nitrogen cycle is carried out by specific, named bacteria, and recalling which bacteria are involved helps confirm which process the question is describing.

1. Nitrate assimilation: This step is carried out by plants and some microbes taking up nitrate for growth, not by bacteria oxidising ammonia, so the organisms involved do not match this question.
2. Nitrification: This step is carried out by Nitrosomonas, which oxidises ammonia to nitrite, followed by Nitrobacter, which oxidises nitrite to nitrate, precisely the ammonia-to-nitrate pathway named in the question.
3. Ammonia assimilation: This step involves enzymes such as glutamine synthetase incorporating ammonia into organic compounds, a route that bypasses nitrate formation entirely.
4. Denitrification: This step is carried out by denitrifying bacteria such as Pseudomonas, converting nitrate into nitrogen gas, the reverse of what the question describes.

Matching the specific bacteria responsible for each transformation confirms that nitrification is the ammonia-to-nitrate process being asked about.

Therefore, the correct answer is Nitrification.