Transpiration is unavoidable evil because of

Options

A. Structure of leaf and harmful effect
B. Beneficial and harmful effect
C. Maintenance of turgidity for growth
D. Gaseous exchange for photosynthesis and respiration

Answer

**Step-by-Step Text Solution:**

1. **Understanding Transpiration**: Transpiration is the process where water vapor is lost from the aerial parts of plants, primarily through small openings called stomata. It is a natural and essential process for plants.

2. **Identifying the Role of Stomata**: Stomata are small pores located mainly on the underside of leaves. They play a crucial role in gas exchange, allowing carbon dioxide to enter for photosynthesis and oxygen to exit as a byproduct.

3. **Linking Transpiration to Photosynthesis and Respiration**: While stomata facilitate essential gas exchange, they also allow water vapor to escape. This loss of water is a necessary trade-off for the plant to maintain its metabolic functions, including photosynthesis and respiration.

4. **Considering the Consequences of Transpiration**: Although transpiration is vital for nutrient uptake and cooling the plant, excessive water loss can lead to wilting and stress, especially in conditions of water scarcity. This highlights the dual nature of transpiration as both beneficial and potentially harmful.

5. **Evaluating the Options**:
- Option A suggests that transpiration is harmful due to the structure of the leaf, which is not entirely accurate.
- Option B mentions both beneficial and harmful effects, but does not pinpoint the primary reason for transpiration being unavoidable.
- Option C states that it is necessary for maintenance of turgidity, which is true but does not encompass the broader implications of gas exchange.
- Option D emphasizes the importance of gaseous exchange for photosynthesis and respiration, which is a fundamental reason why transpiration is unavoidable.

6. **Conclusion**: The correct answer is option D, as it encapsulates the essential role of transpiration in facilitating gas exchange necessary for photosynthesis and respiration, despite its potential drawbacks.