In vertebrates , laying down of bone is often preceded by

Options

A. Cartilage
B. Chitin
C. Platelets
D. Starch.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks what precedes the laying down of bone in vertebrates. This means we need to identify the material or structure that is formed before bones are developed.

2. **Evaluating the Options**:
- **Cartilage**: This is a type of specialized connective tissue found in various parts of the body, including joints and between bones.
- **Chitin**: This is a polysaccharide that makes up the exoskeleton of arthropods and is not found in vertebrates.
- **Platelets**: These are small cell fragments in the blood involved in clotting, not related to bone formation.
- **Starch**: This is a carbohydrate used for energy storage in plants and is not involved in bone formation.

3. **Identifying the Correct Answer**: Among the options, cartilage is the only structure that is directly involved in the process of bone formation in vertebrates. During the development of bones, especially in the embryonic stage, cartilage serves as a precursor to bone tissue.

4. **Conclusion**: Therefore, the correct answer is **cartilage** (Option A). It is the material that precedes the laying down of bone in vertebrates.

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