The secondary wall is chiefly composed of

Options

A. lignin
B. pectin
C. murein
D. chitin

Answer

**Step-by-Step Solution:**

1. **Understanding the Cell Wall Structure:**
- The cell wall of plants is composed of two main layers: the primary wall and the secondary wall. The primary wall is formed first and is flexible, allowing for cell growth.

2. **Identifying the Components of the Secondary Wall:**
- The secondary wall is formed after the primary wall and is thicker and more rigid. It is primarily responsible for providing structural support to the plant.

3. **Key Components of the Secondary Wall:**
- The secondary wall is chiefly composed of **lignin**, which is a complex organic polymer that adds rigidity and impermeability to the cell wall.

4. **Eliminating Other Options:**
- **Pectin** is primarily found in the primary cell wall, providing flexibility and adhesion between cells.
- **Murine** is a component of the bacterial cell wall and does not pertain to plant cells.
- **Chitin** is found in the cell walls of fungi and in the exoskeletons of arthropods, not in plant cell walls.

5. **Conclusion:**
- Therefore, the secondary wall is chiefly composed of **lignin**.

**Final Answer:**
The secondary wall is chiefly composed of **lignin**.

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