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 is the central, non-living part of a tree trunk, formed from the secondary xylem. It is typically darker in color compared to the outer sapwood.

2. **Composition of Heartwood**: The durability and resistance of heartwood to microbes and insects are primarily due to the deposition of various organic compounds within it. These compounds include resins, tannins, oils, gums, and aromatic substances.

3. **Properties of Organic Compounds**:
- **Resins**: These are sticky substances that can help seal wounds and deter insects.
- **Tannins**: These compounds can inhibit the growth of fungi and bacteria.
- **Oils and Aromatic Substances**: These can have antimicrobial properties and can repel insects.

4. **Evaluating Options**:
- Option 1 (secretion of antibiotics) is incorrect because heartwood does not secrete antibiotics.
- Option 3 (living nature) is incorrect as heartwood is non-living.
- Option 4 (presence of highly lignified cells with dense protoplasm) is also incorrect as it does not specifically explain the resistance to microbes and insects.

5. **Conclusion**: The correct answer is that heartwood is durable and resistant to the attacks of microbes and insects due to the deposition of organic compounds.

### Final Answer:
Heartwood is durable and resistant to the attacks of microbes and insects due to the deposition of organic compounds.

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