Which of the following species does not have the ability to fix atmospheric nitrogen?
1)Azotobactor
2) Anabaena
3) Nostoc
4) Spirogyra

Options

A. Azotobactor
B. Anabaena
C. Nostoc
D. Spirogyra

Answer

To determine which species does not have the ability to fix atmospheric nitrogen, we will analyze each option provided:

1. **Azotobacter**:
- Azotobacter is a free-living bacterium known for its ability to fix atmospheric nitrogen. It converts nitrogen gas (N₂) into ammonia (NH₃), which can be utilized by plants.
- **Conclusion**: Azotobacter can fix nitrogen.

2. **Anabaena**:
- Anabaena is a filamentous cyanobacterium that also possesses the ability to fix atmospheric nitrogen. It can convert nitrogen gas into ammonia, and it often exists in symbiotic relationships with certain plants.
- **Conclusion**: Anabaena can fix nitrogen.

3. **Nostoc**:
- Nostoc is another type of cyanobacteria that is capable of nitrogen fixation. It can convert atmospheric nitrogen into ammonia and is often found in symbiotic relationships as well.
- **Conclusion**: Nostoc can fix nitrogen.

4. **Spirogyra**:
- Spirogyra is a filamentous green algae. Unlike the other organisms listed, Spirogyra does not have the ability to fix atmospheric nitrogen. It primarily relies on photosynthesis and does not convert nitrogen gas into ammonia.
- **Conclusion**: Spirogyra cannot fix nitrogen.

Based on the analysis, the species that does not have the ability to fix atmospheric nitrogen is **Spirogyra**.

### Final Answer:
**Spirogyra** does not have the ability to fix atmospheric nitrogen.