Select a correct statement

Options

A. Blue light inhibits opening of stomata
B. PMA (Phenyl mercuric acetate ) is a fungicide as well as an antitranspirant
C. Transpiration does not perform evaporative cooling of leaf surface
D. Transpiration increase when the relative humidity is high

Answer

To solve the question of selecting the correct statement regarding plant transport, we will analyze each of the four statements provided:

1. **Blue light inhibits the opening of stomata.**
- This statement is incorrect. Blue light actually stimulates the opening of stomata. It promotes stomatal opening by suppressing the release of anions from guard cells and reducing the levels of abscisic acid, which is a hormone that promotes stomatal closure.

2. **PMA (Phenylmercuric Acetate) acts as a fungicide and anti-transpirant.**
- This statement is correct. PMA is indeed a chemical that acts as a fungicide, killing fungi, and it also functions as an anti-transpirant by promoting the closure of stomata, thereby reducing transpiration. Prolonged contact with PMA can damage guard cells and inhibit transpiration.

3. **Transpiration does not perform evaporative cooling of the leaf surface.**
- This statement is incorrect. Transpiration is the process of water loss from the aerial parts of the plant, primarily through leaves, and it does indeed provide a cooling effect through evaporative cooling. Therefore, this statement is false.

4. **Transpiration increases when relative humidity is high.**
- This statement is also incorrect. Transpiration is inversely related to humidity; when relative humidity is high, the rate of transpiration decreases because the air is already saturated with moisture, reducing the gradient for water vapor to leave the plant.

**Conclusion:**
The correct statement is **option B: PMA is a fungicide as well as an anti-transpirant.**