gas exchange in plants

• Dicotyledonous leaf structure


  • Lower side has most stomata
  • Spongy mesophyll has space for gas diffusion
  • Palisade mesophyll has cells packed with chloroplasts for photosynthesis
  • Vascular bundle contains xylem and phloem
• Stomata


  Pores formed by guard cells that allow gas exchange
• Gas exchange in leaves

  1. Carbon dioxide diffuses in

  2. Oxygen diffuses out
• Concentration gradient of carbon dioxide and oxygen

  • Lower concentration of carbon dioxide in spongy mesophyll compared to atmosphere, so carbon dioxide diffuses in
  • Higher concentration of oxygen in spongy mesophyll compared to atmosphere, so oxygen diffuses out
• Photosynthesis mainly occurs during the day when stomata are open
• Stomata close at night to reduce water loss
• Xerophytic plants


  • Curled leaves to trap moisture
  • Hairy structures to trap evaporated water
  • Sunken stomata to reduce evaporation
  • Thicker cuticle to prevent evaporation
  • Longer root network to access water
• Marine grass is an example of a xerophytic plant found in sand dunes near the sea