Silk is formed of

Options

A. Fibroin
B. Collagen
C. Elastin
D. myosin.

Answer

**Step-by-Step Solution:**

1. **Understanding Silk Composition**: Silk is primarily composed of proteins. The two main proteins found in silk are fibroin and sericin.

2. **Identifying the Proteins**: Among the options provided:
- **Fibroin**: This is the main structural protein in silk.
- **Collagen**: This is a protein found in connective tissues in animals, not in silk.
- **Elastin**: This protein provides elasticity to tissues, but is not related to silk.
- **Myosin**: This is a muscle protein involved in contraction and relaxation, not in silk formation.

3. **Source of Silk**: Silk is produced by the silkworm, specifically from the larva stage. The fibroin is secreted by the silkworm to form the cocoon.

4. **Amino Acid Sequence**: Fibroin is made up of a specific sequence of amino acids, including glycine and alanine, which contribute to its structural properties.

5. **Conclusion**: Based on the information, the correct answer to the question "Silk is formed of" is **fibroin**.

**Final Answer**: Silk is formed of **fibroin**.

---