Stomata (CIE A Level Biology)

• Plants carry out homeostasis – just like animals they need to maintain a constant internal environment
  • For example, mesophyll cells in leaves require a constant supply of carbon dioxide for photosynthesis

• Stomata (specifically the guard cells) control the diffusion of gases in and out of leaves
  • This means stomata control the entry of carbon dioxide into leaves

Response of guard cells & stomata table

• Regulation of stomatal aperture balances the need for carbon dioxide uptake by diffusion with the need to minimise water loss by transpiration

Advantages & disadvantages of stomatal opening & closure table

• Stomata open and close in a daily rhythm
  • Even when the plant is kept in constant light or constant darkness, the daily rhythm of opening and closing of the stomata continues

• 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