Prokaryotic flagellum consists of

Options

A. Fibre enclosed by protein membrane
B. Fibre enclosed by unit membrane
C. Helically arranged protein molecules
D. Membrane enclosed 9+2 microtubular structure.

Answer

### Step-by-Step Solution:

1. **Understanding the Flagellum**:
- A flagellum is a long, thread-like structure that extends from certain cells or unicellular organisms. It functions primarily as an organ of locomotion, helping the organism to move.

2. **Structure of Prokaryotic Flagellum**:
- The prokaryotic flagellum consists of three main parts:
- **Filament**: This is the longest part of the flagellum, extending from the cell surface to the tip.
- **Hook**: This connects the filament to the basal body.
- **Basal Body**: This anchors the flagellum to the cell wall and membrane.

3. **Composition of the Filament**:
- The filament is a hollow, rigid cylinder made up of a single type of protein known as **flagellin**.

4. **Arrangement of Protein Molecules**:
- The protein molecules (flagellin) in the filament are arranged in a **helical** (spiral) manner.

5. **Identifying the Correct Option**:
- Given the options provided:
- Option 1: Fiber enclosed by protein membrane
- Option 2: Fiber enclosed by unique membrane
- Option 3: Helically arranged protein molecules
- Option 4: Membrane enclosed 9 + 2 microtubular structure
- The correct answer is **Option 3: Helically arranged protein molecules**, as this accurately describes the structure of the prokaryotic flagellum.