Heartwood is durable and resistant to the attacks of microbes and insects due to

Options

A. Secretion of antibiotics
B. Deposition of organic compounds
C. Living nature
D. Presence of highly lignified cells with dense protoplasm

Answer

**Step-by-Step Solution:**

1. **Understanding Heartwood**: Heartwood, also known as duramen, is the central part of a tree trunk. It is typically darker and denser than the surrounding wood (sapwood) and is composed of dead cells.

2. **Characteristics of Heartwood**: Heartwood is known for its durability and resistance to decay, insects, and microbial attacks. This is crucial for the longevity of the tree and its structural integrity.

3. **Reasons for Durability**:
- **Secretion of Antibiotics**: While some plants may produce antibiotics, heartwood itself does not primarily rely on this mechanism for its durability.
- **Deposition of Organic Compounds**: Heartwood contains various organic compounds such as tannins, resins, and gums. These compounds contribute to its hardness and resistance to pests and pathogens.
- **Living Nature**: Heartwood is not living tissue; it is composed of dead cells, so this option is incorrect.
- **Presence of Highly Lignified Cells with Dense Protoplasm**: While heartwood does contain lignified cells, the term "dense protoplasm" is misleading as the cells are dead and do not have protoplasm.

4. **Conclusion**: The primary reason heartwood is durable and resistant to attacks from microbes and insects is due to the deposition of organic compounds, which provide mechanical support and resistance.

5. **Final Answer**: The correct answer is the second option: "deposition of organic compound."

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