In transpiration, cavitation is

Options

A. Rise of water against gravity
B. Evaporation of water in internal spaces
C. Dissolution of air in water
D. Appearance of air bubbles in water.

Answer

**Step-by-Step Solution:**

1. **Understanding Transpiration**: Transpiration is the process by which water evaporates from the internal surfaces of leaves and other aerial parts of a plant. This process is crucial for the movement of water and nutrients from the roots to the leaves.

2. **Identifying Cavitation**: Cavitation refers to the formation of air bubbles within the water column in the xylem vessels. This can disrupt the continuous flow of water, which is essential for effective transpiration.

3. **Analyzing the Options**:
- **Option 1**: "Rise of water against gravity" - This describes the process of water transport but does not define cavitation.
- **Option 2**: "Evaporation of water in the internal space" - This is the definition of transpiration, not cavitation.
- **Option 3**: "Dissolution of air in the water" - While air can dissolve in water, this does not specifically relate to cavitation.
- **Option 4**: "Appearance of air bubbles in the water" - This accurately describes cavitation, as it involves the formation of air bubbles within the xylem vessels.

4. **Conclusion**: Based on the analysis of the options, the correct answer is **Option 4: Appearance of air bubbles in the water**, as this directly relates to the phenomenon of cavitation in the context of transpiration.