Question

how do gaurd cells regulate opening and closing of stomata ?

Answer 1

there are many factors which regulate guard cell

Answer 2

When the plant needs carbon dioxide and sunlight for photosynthesis, the guard cells swell and open so that carbon dioxide and sunlight can enter it. However, if the guard cells remain open, huge amounts of water may be lost from it. So after taking in enough carbon dioxide and sunlight the guard cells shrink causing it to close.