Myosin filament appears dark under microscope due to :

Options

A. Dark colour
B. Melanin colour
C. Black colour
D. Double refractive index

Answer

**Step-by-Step Solution:**

1. **Understanding Myofilaments**: Myofilaments are the contractile proteins found in muscle fibers. There are two main types: myosin (thick filaments) and actin (thin filaments).

2. **Identifying Myosin Filaments**: Myosin filaments are primarily composed of myosin protein. They are thicker compared to actin filaments, which are mainly made of actin protein along with other proteins like tropomyosin and troponin.

3. **Overlapping of Filaments**: In muscle fibers, myosin and actin filaments overlap lengthwise. This overlapping creates a pattern known as striations, which is characteristic of striated muscles.

4. **Refractive Index**: The difference in thickness between myosin and actin filaments leads to a difference in their refractive indices. The refractive index is a measure of how much light is bent, or refracted, when it enters a material.

5. **Why Myosin Appears Dark**: Myosin filaments appear dark under a microscope due to their double refractive index, which is different from that of actin filaments. This difference in refractive index causes myosin to absorb more light, making it appear darker.

6. **Conclusion**: Therefore, the reason myosin filaments appear dark under the microscope is that they have a double refractive index.

**Final Answer**: Myosin filament appears dark under the microscope due to its double refractive index.

---