Question

The increase in rate of transpiration, increases the transpirational pull

• A. Due to increased solute potential in guard cell.
• B. Due to decreased solute potential in epidermal cell.
• C. Due to increased water potential in guard cell.
• D. None of these

Answer 1

Answer: (A)

Due to increased solute potential in guard cell.

Transpiration (evaporation) from the surface of leaves generates a negative pressure in the xylem that pulls water from the roots or soil. This is called the transpirational pull.

The rate of transpirational pull is directly proportional to the rate of transpiration. Guard cells are involved in the regulation of the rate of transpiration by opening and closing of stomata. An increase in solute potential decreases the water potential and water moves from higher potential to lower water potential.

When the potassium level increases in the guard cell, the water potential decreases and promotes the entry of water into guard cells. As a result of which, the cells become turgid (swollen) and the opening of stomata becomes large.

When stomata are open, transpiration increases. In contrast, when cells become flaccid or shrunken (due to decreased level of potassium in guard cell), the stomata close and the rate of transpiration decreases.

So, the correct option is A.