Read the statement regarding myofibril and choose the correct option
1. Each myofibril has alternate dark and light bands.
2. In the centre of each 'A' band is an elastic fibre called 'Z' -line 3. 'A' and 'I' bands are arranged alternately throughout the length of myofibril
4. Sarcomere is the functional unit of contraction
5. Central part of thick filament not overlapped by a thin filament is the 'M' line

Options

A. 1,3 and 5 alone are correct
B. 2 and 5 alone are correct
C. 2 and 3 alone are correct
D. 1,3 and 2 alone are correct.

Answer

To solve the question regarding myofibrils and determine which statements are correct, we will evaluate each statement one by one.

### Step-by-Step Solution:

1. **Evaluate Statement 1**:
- The statement claims that "each myofibril has alternate dark and light bands."
- **Analysis**: This is true. Myofibrils consist of alternating dark bands (A bands) and light bands (I bands). The dark bands are primarily composed of myosin filaments, while the light bands consist of actin filaments.
- **Conclusion**: Statement 1 is correct.

2. **Evaluate Statement 2**:
- The statement claims that "in the center of each 'A' band is an elastic fibre called 'Z' line."
- **Analysis**: This is false. The center of the A band contains the M line, not the Z line. The Z line is actually found at the center of the I band.
- **Conclusion**: Statement 2 is incorrect.

3. **Evaluate Statement 3**:
- The statement claims that "'A' and 'I' bands are arranged alternately throughout the length of myofibril."
- **Analysis**: This is true. The arrangement of A and I bands alternates along the length of the myofibril, contributing to the striated appearance of skeletal muscle.
- **Conclusion**: Statement 3 is correct.

4. **Evaluate Statement 4**:
- The statement claims that "sarcomere is the functional unit of contraction."
- **Analysis**: This statement is somewhat misleading. While the sarcomere is indeed the structural and functional unit of muscle contraction, the phrase "functional unit of contraction" can be seen as incomplete without mentioning its structural role.
- **Conclusion**: Statement 4 is misleading and can be considered incorrect.

5. **Evaluate Statement 5**:
- The statement claims that "the central part of thick filament not overlapped by a thin filament is the 'M' line."
- **Analysis**: This is incorrect. The central part of the thick filament that is not overlapped by thin filaments is referred to as the H zone, while the M line is the line that runs down the center of the A band.
- **Conclusion**: Statement 5 is incorrect.

### Final Conclusion:
- The correct statements are **1 and 3**. Therefore, the correct option is the one that includes these statements.