When do the stomata close?

According to the proton transport theory,which ion plays an important role in the opening and closing of stomata?

Out of the following, which one is the most common type of transpiration?

More water is lost from which surface of a dorsi-ventral leaf?

The stomatal apparatus consists of:

$A-$ The inner wall of each guard cell,towards the pore or stomatal aperture,is thick and elastic.
$R -$ Cellulose microfibrils are oriented longitudinally in the cell walls of the guard cells.