Guard cells

• Have a kidney shape which opens and closes the stomata in a leaf
• When the plant has lots of water the guard cells fill with it and go plump and turgid. This makes the stomata open so gases can be exchanged for photosynthesis
• When the plant is short of water, the guard cells lose water and become flaccid, making the stomata close. This helps stop too much water vapour escaping
• Thin outer walls and thickened inner walls make the opening and closing work
• They're also sensitive to light and close at night to save water without losing out on photosynthesis
• More stomata is found on the undersides of leaves than on he top. The lower surface is shaded and cooler - so less water is lost through the stomata than if it were on the upper surface
• Guard cells are adapted for gas exchange and controlling water loss within a leaf