Which of the following is not a surface structure found in bacteria ?

Options

A. Pilli
B. Flmbriae
C. Flagella
D. Plasmids

Answer

To determine which of the following is not a surface structure found in bacteria, we will analyze each option provided:

1. **Pili**:
- Pili are hair-like appendages found on the surface of bacteria.
- They are made of a protein called pilin and play a significant role in bacterial conjugation, which is a process of genetic recombination.
- Since pili are located on the surface of bacteria, they are considered a surface structure.

2. **Fimbri**:
- Fimbri are also hair-like structures that are proteinaceous and filamentous.
- They are present on the surface of bacterial cells and assist in adhesion, helping bacteria bind to specific receptors on host cells.
- As fimbri are located on the surface of bacteria, they are also considered a surface structure.

3. **Flagella**:
- Flagella are whip-like structures that protrude from the surface of bacteria.
- They are responsible for the motility of bacteria, allowing them to move toward or away from stimuli.
- Since flagella are attached to the surface of bacteria, they are also classified as a surface structure.

4. **Plasmids**:
- Plasmids are small, circular pieces of extra-chromosomal DNA found within the cytoplasm of bacteria.
- They are not attached to the surface of the bacterial cell; instead, they float freely in the cytoplasm.
- Therefore, plasmids are not considered a surface structure.

Based on the analysis above, the answer to the question "Which of the following is not a surface structure found in bacteria?" is **plasmids**.

### Summary of the Solution:
- **Pili**: Surface structure (present on bacterial surface).
- **Fimbri**: Surface structure (present on bacterial surface).
- **Flagella**: Surface structure (present on bacterial surface).
- **Plasmids**: Not a surface structure (located in the cytoplasm).

**Correct Answer**: Plasmids