Question

The process of conversion of nitrogen into ammonia by bacteria is called:

• A. Nitrification
• B. Denitrification
• C. Nitrogen fixation
• D. Ammonification

Hint:

Nitrogen fixation is the only process that directly converts atmospheric nitrogen (N$_2$) into a biologically usable form.

Answer 1

The Correct Option is C

The process of conversion of nitrogen into ammonia by bacteria is called Nitrogen fixation. Let's explore the concept and why this is the correct answer:

1. Nitrogen Fixation: This is the biochemical process through which atmospheric nitrogen gas (N₂) is converted into ammonia (NH₃) by certain bacteria, such as Rhizobium, often found in the root nodules of legumes. This is a crucial step in the nitrogen cycle as it makes nitrogen available in a form that can be absorbed by plants.
2. Nitrification: This process involves the conversion of ammonia into nitrites (NO₂^-) and then to nitrates (NO₃^-) by bacteria. This is not directly related to the conversion of nitrogen gas into ammonia.
3. Denitrification: This is the reduction of nitrates back into the largely inert nitrogen gas (N₂) by certain bacteria, thus removing nitrogen from the soil and releasing it into the atmosphere.
4. Ammonification: This refers to the conversion of organic nitrogen found in dead plants and animals back into ammonia. It is part of the decomposition process and is not the same as nitrogen fixation.

Based on the explanations above, the correct answer is Nitrogen fixation, as it specifically addresses the conversion of nitrogen gas (N₂) into ammonia (NH₃) by bacteria like Rhizobium. The other processes mentioned serve different roles in the nitrogen cycle.

Answer 2

Step 1: Understanding the nitrogen cycle.
Nitrogen is an essential element for living organisms, but atmospheric nitrogen (N$_2$) cannot be directly used by plants and animals. It must first be converted into usable forms such as ammonia or nitrates through various biological processes collectively known as the nitrogen cycle.
Step 2: Understanding nitrogen fixation.
Nitrogen fixation is the process by which atmospheric nitrogen (N$_2$) is converted into ammonia (NH$_3$) by nitrogen-fixing bacteria such as \textit{Rhizobium}, \textit{Azotobacter}, and cyanobacteria. This process makes nitrogen available to plants.
Step 3: Analysis of the given options.
(A) Nitrification: This is the conversion of ammonia into nitrites and nitrates by nitrifying bacteria.
(B) Denitrification: This is the conversion of nitrates back into atmospheric nitrogen.
(C) Nitrogen fixation: Correct — it converts atmospheric nitrogen into ammonia with the help of bacteria.
(D) Ammonification: This is the conversion of organic nitrogen into ammonia during decomposition.
Step 4: Conclusion.
The conversion of nitrogen into ammonia by bacteria is correctly called Nitrogen fixation.