The enzyme that can split a nitrogen molecule during nitrogen fixation is:

Options

A. nitrogenase
B. nitrate reductase
C. nitrite reductase
D. Nitrosomonas

Answer

To answer the question about which enzyme can split a nitrogen molecule during nitrogen fixation, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into a usable form, such as ammonia (NH₃). This process is essential for incorporating nitrogen into biological systems.

2. **Identify the Enzymes**:
- The question provides four options:
- Option 1: Nitrogenase
- Option 2: Nitrate reductase
- Option 3: Nitrite reductase
- Option 4: Nitrosomonas

3. **Evaluate Each Option**:
- **Option 1: Nitrogenase**:
- This enzyme is produced by certain bacteria, including cyanobacteria. It is specifically responsible for the reduction of nitrogen gas (N₂) to ammonia (NH₃). This is the key reaction in nitrogen fixation.
- **Option 2: Nitrate Reductase**:
- This enzyme reduces nitrate (NO₃⁻) to nitrite (NO₂⁻) and is not involved in the direct splitting of nitrogen gas.
- **Option 3: Nitrite Reductase**:
- This enzyme catalyzes the reduction of nitrite to nitric oxide (NO) and does not play a role in nitrogen fixation.
- **Option 4: Nitrosomonas**:
- This is a genus of bacteria involved in nitrification, which uses ammonia as an energy source, but it does not split nitrogen molecules.

4. **Conclusion**:
- After evaluating all the options, it is clear that the enzyme responsible for splitting a nitrogen molecule during nitrogen fixation is **Nitrogenase**.

### Final Answer:
The enzyme that can split a nitrogen molecule during nitrogen fixation is **Nitrogenase**.

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