plants

• when the guard cell is full with water, it becomes TURGID which opens the stomata, letting in CO2 and O2.
• when the guard cell is empty, it becomes FLACCID, which closes the stomata letting nothing inside the plant.
• the stomata are open during the day, and closed at night.
• Opening of stomata during the day

  • Maintains the inward diffusion of carbon dioxide and the outward diffusion of oxygen
  • Allows the outward diffusion of water vapour in transpiration
• Closing of stomata at night when photosynthesis cannot occur


  • Reduces the rate of transpiration
  • Conserves water by closing stoma
• Transpiration

  The loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers)
• Transpiration

  • Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells
  • Diffusion of water vapour through the stomata