Which one of the following organisms has a role in converting ammonia into nitrites ?

Options

A. Rhizobium
B. Nitrobacter
C. Nitrosomonas
D. Pseudomonas

Answer

To solve the question of which organism converts ammonia into nitrites, we will analyze the options provided and their respective roles in the nitrogen cycle.

### Step-by-Step Solution:

1. **Understand the Nitrogen Cycle**: The nitrogen cycle involves various processes where nitrogen is converted into different chemical forms. Key processes include nitrogen fixation, nitrification, denitrification, and ammonification.

2. **Identify the Organisms**: The question provides four options: Rhizobium, Nitrobacter, Pseudomonas, and Nitrosomonas. We need to identify which of these is involved in converting ammonia into nitrites.

3. **Analyze Each Organism**:
- **Rhizobium**: This bacterium is known for nitrogen fixation. It converts atmospheric nitrogen (N2) into ammonia (NH3) but does not convert ammonia into nitrites.
- **Nitrobacter**: This organism is involved in nitrification, but it specifically converts nitrites (NO2-) into nitrates (NO3-), not ammonia into nitrites.
- **Pseudomonas**: This genus includes species that are involved in denitrification, which is the process of converting nitrates back into nitrogen gas (N2) and returning it to the atmosphere.
- **Nitrosomonas**: This bacterium is specifically responsible for the oxidation of ammonia (NH3) to nitrites (NO2-). This is a key step in the nitrification process.

4. **Conclusion**: Based on the analysis, the organism that converts ammonia into nitrites is **Nitrosomonas**.

### Final Answer:
The correct answer is **Nitrosomonas**.

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