When does the stomatal aperture open?

The amount of water transpired by a beech tree in summer is:

Assertion : Light is a very important factor in transpiration.
Reason : Light induces stomatal opening and darkness closing of stomata. Therefore,transpiration increases in light and decreases in dark.

If the rates of transpiration and water absorption of a flowering plant are measured over a period of $24$ hours,it is found that the rate of transpiration reaches its peak at about mid-day and then declines,whereas the peak for water absorption is reached approximately two hours later. Which one of the following statements provides the best explanation of these results?

Transpiration is possible only when the atmospheric factor is...

The loss of water in the form of vapour from aerial plant parts is known as