What is incorrect for Nostoc ?

Options

A. Heterocystous cyanobacteria
B. Presence of mucilaginous sheath
C. Presence of flagellate stage
D. Increases soil fertility

Answer

To determine what is incorrect for Nostoc, we will analyze each of the provided statements about this organism.

### Step-by-Step Solution:

1. **Identify the Characteristics of Nostoc**:
- Nostoc is a genus of cyanobacteria, also known as blue-green algae.
- They are unicellular and prokaryotic organisms.
- Nostoc is capable of photosynthesis, meaning they are autotrophs and can synthesize their own food.

2. **Analyze Each Statement**:
- **Statement 1: Heterocytous cyanobacteria**:
- Nostoc is indeed heterocytous, meaning it has specialized cells called heterocysts that are involved in nitrogen fixation. This statement is correct.

- **Statement 2: Presence of mucilaginous sheath**:
- Nostoc is known to have a mucilaginous sheath that surrounds its cells, which helps in protection and retention of moisture. This statement is also correct.

- **Statement 3: Presence of phleglate stage**:
- Nostoc does not have a phleglate stage. Phleglate refers to the presence of flagella, which are absent in Nostoc. Instead, they move by gliding. This statement is incorrect.

- **Statement 4: Increase in soil fertility**:
- Nostoc contributes to soil fertility through nitrogen fixation, which enriches the soil with nitrogen. This statement is correct.

3. **Conclusion**:
- The incorrect statement regarding Nostoc is the presence of a phleglate stage.

### Final Answer:
The incorrect statement for Nostoc is the **presence of phleglate stage**.

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