Heterocysts specialised for nitrogen fixation, occur in certain

Options

A. Red algae (Batrochospemmum)
B. Green algae (Spirogyra)
C. Blue-green algae (Anabaena)
D. Brown algae (Laminaria)

Answer

### Step-by-Step Solution:

1. **Understanding Heterocysts**:
- Heterocysts are specialized cells found in certain cyanobacteria that are responsible for nitrogen fixation. They are crucial for converting atmospheric nitrogen (N₂) into a form that can be utilized by living organisms.

2. **Identifying the Organisms**:
- The question provides four options:
- Red algae (e.g., Batrocospemum)
- Green algae (e.g., Spirogyra)
- Blue-green algae (e.g., Anabena)
- Brown algae (e.g., Laminaria)

3. **Analyzing Each Option**:
- **Red Algae**: Batrocospemum does not have heterocysts for nitrogen fixation.
- **Green Algae**: Spirogyra also does not have heterocysts.
- **Blue-Green Algae**: Anabena is known for having heterocysts that facilitate nitrogen fixation.
- **Brown Algae**: Laminaria does not possess heterocysts.

4. **Conclusion**:
- Based on the analysis, the only group that contains heterocysts specialized for nitrogen fixation is the blue-green algae, specifically Anabena.

5. **Final Answer**:
- The correct answer is **blue-green algae (Anabena)**.