Wood is

Options

A. primary xylem
B. secondary xylem
C. primary phloem
D. secondary phloem

Answer

### Step-by-Step Solution:

1. **Understanding Wood**: Wood is primarily composed of xylem tissue. In vascular plants, wood is formed as a result of secondary growth.

2. **Identifying Types of Xylem**: There are two types of xylem: primary xylem and secondary xylem. Primary xylem is formed during the initial stages of plant growth, while secondary xylem is produced later through the activity of the vascular cambium.

3. **Role of Vascular Cambium**: The vascular cambium is a layer of meristematic tissue that divides to produce secondary xylem (wood) towards the inside and secondary phloem (bark) towards the outside.

4. **Composition of Wood**: The secondary xylem consists mainly of dead cells that facilitate the transport of water and minerals. It also provides structural support to the plant.

5. **Differentiating Wood Types**: Within the secondary xylem, there are two types of wood:
- **Sapwood**: This is the active part of the wood that contains water and stores nutrients.
- **Heartwood**: As the plant ages, the inner part of the secondary xylem becomes inactive, losing its water and stored nutrients, and is referred to as heartwood.

6. **Conclusion**: Based on the information, wood is defined as secondary xylem, which is the result of secondary growth in xylem tissue.

### Final Answer:
Wood is secondary xylem.

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