The structural and functional unit of myofibrill which contracts to cause movement is called

Options

A. Sarcolemma
B. Sarcomere
C. Fascia
D. Myosin

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the structural and functional unit of myofibril that contracts to cause movement.

2. **Identifying Key Terms**:
- Myofibril: These are the basic rod-like units of a muscle cell.
- Contract: Refers to the shortening and thickening of muscle fibers to produce movement.

3. **Exploring Myofibril Structure**:
- Myofibrils are made up of repeating units called sarcomeres.
- Each sarcomere contains thick and thin filaments which are responsible for muscle contraction.

4. **Defining Sarcomere**:
- The sarcomere is defined as the structural and functional unit of a myofibril.
- It is the segment between two Z lines and is responsible for the contraction of muscle fibers.

5. **Understanding the Components**:
- The sarcomere consists of:
- A bands (dark bands) which contain thick filaments (myosin).
- I bands (light bands) which contain thin filaments (actin).
- Z lines that bisect the I bands and anchor the thin filaments.

6. **Conclusion**:
- Since the sarcomere is the unit that contracts and causes movement in muscle fibers, the answer to the question is **"sarcomere."**

---