Which one of the following can fix nitrogen?

Options

A. Wuchereria
B. Spirogyra
C. Nostoc
D. Ectocarpus.

Answer

To determine which of the given organisms can fix nitrogen, we will analyze each option based on their characteristics and abilities.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process through which atmospheric nitrogen (N₂) is converted into a form that plants can use, typically ammonia (NH₃). This process is primarily carried out by certain microorganisms.

2. **Analyzing the Options**:
- **Option 1: Vichroria**:
- Vichroria is a parasite belonging to the Ascaris genus (roundworms). It is not involved in nitrogen fixation.
- **Conclusion**: This option does not fix nitrogen.

- **Option 2: Spirogyra**:
- Spirogyra is a green alga. While it is photosynthetic, it does not have the capability to fix atmospheric nitrogen.
- **Conclusion**: This option does not fix nitrogen.

- **Option 3: Nostoc**:
- Nostoc is a type of blue-green algae (cyanobacteria) known for its ability to fix atmospheric nitrogen. It contains specialized cells called heterocysts that provide an anaerobic environment for the nitrogen-fixing enzyme, nitrogenase, to function.
- **Conclusion**: This option does fix nitrogen.

- **Option 4: Ectocarpus**:
- Ectocarpus is a brown alga. Like Spirogyra, it does not have the ability to fix atmospheric nitrogen.
- **Conclusion**: This option does not fix nitrogen.

3. **Final Answer**:
- Based on the analysis, the organism that can fix nitrogen from the given options is **Nostoc**.