2.43B Role of Stomata in Gas Exchange (Edexcel IGCSE Biology)

• Stomata are spaces found between two guard cells predominantly on the lower epidermis of the leaf
• The guard cells are responsible for the opening and closing of the stomatal pore which controls gas exchange and water loss
• Stomata open when water moves (by osmosis) into the guard cells causing them to become turgid
  • This allows gases to diffuse in and out of the leaf through the stomatal pore
  • Stomata tend to open when there is plenty of water and sunlight

• Stomata close when the guard cells lose water (by osmosis) to the neighbouring epidermal cells and they become flaccid
  • This prevents any diffusion into or out of the leaf
  • Stomata tend to close due to low water availability or low sunlight

The guard cells control the opening and closing of the stomata