Question

The rate of transpiration is high when

• A. The atmosphere is saturated with water vapour.
• B. Light is very dim.
• C. The temperature is low.
• D. The atmosphere is dry and the temperature is high.

Answer 1

The correct option is D The atmosphere is dry and the temperature is high.

The light affects indirectly the atmosphere. The rate of transpiration is always higher in light than in darkness. The main reason is that the stomata remain open in the presence of light or in the day time, and the transpiration takes place through them. In the absence of light or in the night, the stomata remain closed, and the transpiration is checked. During night, only lenticular and cuticular transpiration takes place. The leaves receive heat from the sun, which accelerates the rate to some extent.
As the atmospheric temperature rises, the rate of transpiration also rises. With high temperature the water evaporates from the leaf surface quite rapidly. In dry and hot air the rate of transpiration rises further.