guard cells

• guard cells are adapted to open and close stomata
• they 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 water and go plump and turgid - this makes the stomata open so gases can be exchaned for photsynthesis
• 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 are also sensitive to light and close at night to save water without losing out on photosynthesis
• stomata are usually on the underside of leaves - this is because the underside is shaded and cooler, so less water is lost through the stomata than if they were on the top surface
• guard cells are therefore adapted for gas exchange and controlling water loss within a leaf