Question

Assertion (A): Stomata are generally open in the light and close in the dark.

Reason (R): Transpiration is enhanced by the heating effect of light.

Options

• Both A and R are true and R is the correct explanation of A.

• Both A and R are true but R is not the correct explanation of A.

• A is true but R is false.

• A is false but R is true.

Answer 1

Both A and R are true but R is not the correct explanation of A.

Explanation:

The assertion is true because light triggers a series of biochemical changes (like the potassium ion pump mechanism) that cause guard cells to swell and open stomata during the day and close them at night. The reason is also true because light introduces radiant energy that heats leaves, providing the latent heat required to speed up water evaporation. However, the reason is not the correct explanation of the assertion, as the heating effect of light on evaporation rates is a physical factor that accelerates water loss, rather than the biological mechanism that forces stomata to physically open or close.