Which of the following can use elemental nitrogen as their nitrogen source

Options

A. anabaena
B. Nitrobacter
C. Nitrosomonas
D. All of the above

Answer

To determine which organisms can use elemental nitrogen (N2) as their nitrogen source, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which organisms can utilize elemental nitrogen (N2) as their nitrogen source.

2. **Evaluate the First Option - Anabena**:
- Anabena is a type of cyanobacteria known for its ability to fix atmospheric nitrogen.
- It possesses specialized cells called heterocysts that allow it to convert N2 into ammonia, which can be used for growth.
- **Conclusion**: Anabena can use elemental nitrogen as its nitrogen source. This option is correct.

3. **Evaluate the Second Option - Nitrobacter**:
- Nitrobacter is a genus of bacteria that plays a role in the nitrogen cycle by oxidizing nitrite (NO2-) to nitrate (NO3-).
- It does not have the capability to fix atmospheric nitrogen (N2).
- **Conclusion**: Nitrobacter cannot use elemental nitrogen as its nitrogen source. This option is incorrect.

4. **Evaluate the Third Option - Nitrosomonas**:
- Nitrosomonas is another genus of bacteria involved in the nitrogen cycle, specifically in the oxidation of ammonia (NH3) to nitrite (NO2-).
- Similar to Nitrobacter, it does not fix atmospheric nitrogen.
- **Conclusion**: Nitrosomonas cannot use elemental nitrogen as its nitrogen source. This option is incorrect.

5. **Final Conclusion**:
- The only organism among the options that can use elemental nitrogen (N2) as its nitrogen source is Anabena.
- Therefore, the correct answer is **Option 1: Anabena**.