In Bacterial flagellum the longest portion is:

Options

A. A. Filament
B. B. Hook
C. C. Basal body
D. D. Pili

Answer

**Step-by-Step Solution:**

1. **Understanding the Bacterial Flagellum Structure:**
- The bacterial flagellum is composed of three main parts: the filament, the hook, and the basal body. Each part has a specific function in the structure and movement of the flagellum.

2. **Identifying the Longest Portion:**
- Among the three parts, the filament is the longest portion of the bacterial flagellum. It is a long, whip-like structure that extends out from the cell and is responsible for the propulsion of the bacterium.

3. **Analyzing Other Options:**
- **Hook:** The hook is a curved structure that connects the filament to the basal body. It is shorter than the filament.
- **Basal Body:** The basal body is the part of the flagellum that anchors it to the cell wall and membrane. It is also shorter than the filament and acts as the motor for flagellar movement.
- **Pili:** Pili are hair-like structures used for attachment and DNA transfer, and they are not part of the flagellum structure.

4. **Conclusion:**
- Since the filament is the longest portion of the bacterial flagellum, the correct answer is **A. Filament**.