Basically, guard cells are cells surrounding
each stoma and they help to set the rate of transpiration by opening and
closing the stomata. Some guard cells are turgid or swollen and the stomatal
opening is large. Hence ths turgidity is caused by the accumulation of the
potassium ions in the guard cells. Thus, when the potassium ions or K+ levels happen
to increase in the guard cells the water potential of the guard cells drops and
water enters the guard cells. Some guard cells have lost water which causes the
cells to become flaccid and the stomatal opening to close. This may occur when
the plant has lost an exessive amount of water. Moreover guard cells function
are the stomatal closing and the stomatal opening of the plant.
