The opening and closing of stomata is controlled by the activity of

Transpiration increases by

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?

$A$ are structures present in the epidermis of leaves. They regulate the process of transpiration and $B$ exchange. It is composed of two bean-shaped cells known as $C$ cells.
Choose the correct combination of $A, B$ and $C$ from the following options:

Of the processes which occur in leaves,the one which may lower their temperature (cooling effect) is

In which of the following situations would the transpiration rate be least affected by changes in humidity or temperature?