Question

How can it be that as the guard cells swell up the stomata opens. If both the guard cells will swell up then the stomata must close and not open and if the guard cells shrink they must open according to me.

But why is it not so??

Answer 1

When guard cells swell the turgor pressure in the guard cell increases and opens the stomata pore. When water moves out of the guard cell the cell becomes flaccid as the turgor pressure inside the guard cell decreases. This leads to closure of stomata. In flaccid condition they shrink so stomata gets close but when guard cells are swollen they become inflated which uncovers the stomatal pore.