gas exchange in plants

• key layers of a leaf for gas exchange:

  • stomata - the gap between 2 guard cells which is the exact site of gas exchange
  • spongey mesophyll - once gases diffuse in they go into the air spaces which helps maintain a concentration gradient
  • palisade mesophyll - where most photosynthesis occurs as its closest to top surface so will receive most sunlight
• gas exchange at the stomata:

  • oxygen diffuses out
  • CO2 diffuses in
  • to reduce water loss by evaporation, stomata close at night when photosynthesis wouldn't be occurring
• xerophytic plants are adapted to survive in environments with limited water, so have structural features to enable efficient gas exchange to occur whilst also limiting water loss
• adaptations of xerophytes:

  • curled leaves - trap moisture to increase local humidity, therefore decreasing water potential gradient so less evaporation
  • hairs - trap moisture to increase local humidity
  • sunken stomata - trap moisture to increase local humidity
  • thicker cuticle - reduce evaporation
  • longer root network - reach more water