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 about Nostoc, we will analyze each of the provided statements one by one.

### Step 1: Analyze the first statement - "Heterocystocynovacteria"
- **Explanation**: Heterocysts are specialized cells in Nostoc that are involved in nitrogen fixation. They form under nitrogen-starvation conditions.
- **Conclusion**: This statement is correct.

### Step 2: Analyze the second statement - "Presence of the mucilaginous sheath"
- **Explanation**: Nostoc secretes a mucilaginous sheath that helps in binding sand particles and provides protection.
- **Conclusion**: This statement is also correct.

### Step 3: Analyze the third statement - "Presence of the flagellate stage"
- **Explanation**: Nostoc does not have a flagellate stage. It exists primarily in a filamentous form and does not exhibit motility through flagella.
- **Conclusion**: This statement is incorrect.

### Step 4: Analyze the fourth statement - "Increases soil fertility"
- **Explanation**: Nostoc is known for its ability to fix atmospheric nitrogen, which contributes to soil fertility.
- **Conclusion**: This statement is correct.

### Final Conclusion:
The incorrect statement regarding Nostoc is the third one: "Presence of the flagellate stage."

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