Physiologically functional part of wood is

Options

A. Heart wood only
B. Sap wood only
C. Only primary wood
D. Both heart wood & sap wood

Answer

### Step-by-Step Solution:

1. **Understanding Wood Structure**: Wood is primarily composed of two types of xylem: primary xylem and secondary xylem. The secondary xylem is formed as trees grow older and is responsible for most of the wood's structure.

2. **Identifying Components of Wood**: In older trees, the secondary xylem undergoes changes due to the deposition of various organic substances such as tannins, resins, oils, gums, and aromatic compounds. These deposits contribute to the wood's hardness and durability.

3. **Distinguishing Between Types of Wood**: The secondary xylem can be divided into two parts:
- **Heartwood**: The inner part, which becomes dark brown due to the deposition of substances. It is highly lignified and provides mechanical support but does not conduct water or nutrients.
- **Sapwood**: The outer part, which is lighter in color and is responsible for the conduction of water and minerals.

4. **Function of Sapwood**: The sapwood is the physiologically functional part of the wood because it actively conducts water and minerals from the roots to the leaves of the plant.

5. **Conclusion**: Therefore, the physiologically functional part of wood is the **sapwood**.