Nebenkern sheath is restricted to

Options

A. Tail of sperm
B. Acrosome of sperm
C. Head of sperm
D. energy - chamber of sperm

Answer

### Step-by-Step Solution:

1. **Understanding Sperm Structure**: The sperm is composed of three main parts: the head, mid-piece (or middle piece), and tail. Each part has specific functions and structures.

2. **Identifying the Components**:
- **Head**: Contains the nucleus and the acrosome, which is important for penetrating the egg.
- **Mid-piece**: Characterized by the presence of abundant mitochondria that provide energy for sperm motility.
- **Tail**: Contains the axial filament (flagella) that aids in the movement of the sperm.

3. **Focus on the Mid-piece**: The mid-piece of the sperm is crucial because it houses the mitochondria, which are responsible for energy production.

4. **Mitochondrial Arrangement**: In the mid-piece, the mitochondria are not just randomly distributed; they are fused together to form a specific structure.

5. **Defining Nebenkern Sheath**: The fused mitochondria in the mid-piece create a spiral or aggregate structure known as the Nebenkern sheath.

6. **Evaluating the Options**:
- **Tail of Sperm**: Incorrect, as the Nebenkern sheath is not found here.
- **Acrosome of Sperm**: Incorrect, as this structure is located in the head of the sperm.
- **Head of Sperm**: Incorrect, as the Nebenkern sheath is not present in the head.
- **Energy Chamber of Sperm**: Correct, as this refers to the mid-piece where the Nebenkern sheath is located.

7. **Conclusion**: The Nebenkern sheath is restricted to the mid-piece of the sperm, which serves as the energy chamber due to the presence of the mitochondria.

### Final Answer:
The Nebenkern sheath is restricted to the **mid-piece of sperm** (also referred to as the energy chamber).

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