Which of the following is incorrect about a bacterial cell ?

Options

A. The 70S ribosome is mainly associated with plasma membrane and many a times shows polysome assembly.
B. The filament is the longest portion of the flagella and extends from the cell surface to the outside .
C. The plasma membrane extensions containing chromatophores basically helps in cellular respiration .
D. Gram staining is basically based on the thickness of peptidoglycan layer.

Answer

To solve the question "Which of the following is incorrect about a bacterial cell?", we will analyze each of the provided statements regarding bacterial cells.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- "The 70S ribosome is mainly associated with a plasma membrane and many times shows polysome assembly."
- **Analysis**: This statement is correct. In bacterial cells, 70S ribosomes are indeed associated with the plasma membrane and can form polysomes, which are clusters of ribosomes translating the same mRNA.

2. **Evaluate the Second Statement**:
- "The filament is the longest portion of the flagella and extends from the cell surface to the outside."
- **Analysis**: This statement is also correct. The filament is indeed the longest part of the bacterial flagella, extending from the surface of the cell into the external environment.

3. **Evaluate the Third Statement**:
- "The plasma membrane extension containing chromatophores basically helps in cellular respiration."
- **Analysis**: This statement is incorrect. Chromatophores are pigment-containing structures found in some bacteria that are involved in photosynthesis, not cellular respiration. They do not primarily function in respiration but rather in capturing light energy.

4. **Evaluate the Fourth Statement**:
- "Gram staining is basically based on the thickness of the peptidoglycan layer."
- **Analysis**: This statement is correct. Gram staining differentiates bacteria based on the thickness of their peptidoglycan layer, which is crucial for identifying Gram-positive and Gram-negative bacteria.

### Conclusion:
The incorrect statement about a bacterial cell is the third statement: "The plasma membrane extension containing chromatophores basically helps in cellular respiration."

### Final Answer:
**Option 3 is incorrect.**

---