During contraction of a skeletal muscle :

Options

A. A - band shortens
B. I - band remain same
C. I - band shortens
D. Z - line is stretched

Answer

### Step-by-Step Solution:

1. **Understanding Muscle Contraction**:
- Skeletal muscles contract to facilitate movement, which is essential for locomotion. When a muscle contracts, it generates force and shortens in length.

2. **Structure of the Sarcomere**:
- The sarcomere is the basic functional unit of a skeletal muscle. It consists of:
- **I-band**: Contains actin filaments and is lighter in color.
- **A-band**: Contains myosin filaments and is darker.
- **Z-line**: The boundary between adjacent sarcomeres.

3. **Changes During Contraction**:
- When a skeletal muscle contracts:
- The **I-band** shortens as the actin filaments slide over the myosin filaments.
- The **A-band** remains the same length because the myosin filaments do not change in length.
- The **Z-lines** move closer together as the muscle contracts, but they do not become straight; they remain in place.

4. **Analyzing the Options**:
- **Option A**: A-band shortens - Incorrect. The A-band does not shorten during contraction.
- **Option B**: I-band remains the same - Incorrect. The I-band shortens during contraction.
- **Option C**: I-band shortens - Correct. This is the hallmark of muscle contraction.
- **Option D**: Z-line is straight - Incorrect. The Z-line does not become straight; it moves closer together.

5. **Conclusion**:
- The correct answer is that during the contraction of a skeletal muscle, the **I-band shortens**.