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 option provided and determine which statement is false.

### Step-by-Step Solution:

1. **Understanding Bacterial Cell Structure**:
- Bacterial cells are prokaryotic, meaning they lack a well-defined nucleus. Instead, their genetic material (DNA) is located in a region called the nucleoid.
- They have a cell wall, plasma membrane, cytoplasm, ribosomes, and may have structures like flagella and pili.

2. **Analyzing Each Option**:
- **Option 1**: "70S ribosome is mainly associated with the plasma membrane."
- This statement is true. Bacterial ribosomes are 70S and are often found associated with the plasma membrane.

- **Option 2**: "The filament is the longest portion of the flagella."
- This statement is also true. The flagella consist of three parts: the basal body, hook, and filament, with the filament being the longest part.

- **Option 3**: "The plasma membrane extensions containing the chromatophore basically helps in cellular respiration."
- This statement is incorrect. Chromatophores are membrane extensions found in some bacteria (like cyanobacteria) that are involved in photosynthesis, not cellular respiration.

- **Option 4**: "The gram staining is basically dependent upon the peptidoglycan layer."
- This statement is true. The thickness of the peptidoglycan layer determines whether bacteria are gram-positive or gram-negative based on their ability to retain the gram stain.

3. **Identifying the Incorrect Statement**:
- After analyzing all options, the third statement is the only incorrect one since chromatophores are involved in photosynthesis, not cellular respiration.

### Conclusion:
The incorrect statement about a bacterial cell is **Option 3**: "The plasma membrane extensions containing the chromatophore basically helps in cellular respiration."