Gas Exhange in Plants

• Gas Exchange in Plants

  Plants use their leaves to exchange gases with the environment
• Stomata


  • Found on the outer tissue of plant's leaves
  • Allow gases (CO2(g), H2O(g) and O2(g)) to diffuse (passive transport) into and out of the leaf
  • Maximize gas exchange
• Gas exchange in leaves

  1. Gases diffuse through the cell membranes of the spongy tissue cells

  2. Gases circulate between the spongy and palisade tissue cells
• Gas exchange in plants

  • A small amount of gas exchange also occurs at the surface of the roots and in the stem of the plant
  • In bark covered plants, layers of dead cork cells and the waxy cuticle prevent direct gas exchange from occurring
  • Lenticels, a lens shaped opening found on the bark, allows for the exchange of gases with the environment
• Gas exchange in plants

  Causes loss of water (transpiration)
• Stomata


  Used by plants to retain water
• Stomata open


  CO2(g) can enter and O2(g) and H2O(g) can leave, therefore high rates of photosynthesis are observed
• Stomata closed


  Gas exchange and water loss are reduced
• Most plants open stomata during the day and close at night, except in very dry conditions like the desert where the stomata will open at night
• Stomata


  • Found in the epidermis on the top and underside of the leaf that open into air chambers that transport the gases to the ground tissue
  • Direction of gas movement into and out of the stomata is based on diffusion down concentration gradients
  • Guard cells form the tiny opening known as stomata
• Guard cells


  • The amount of water within the guard cells determines if they are open or closed
  • Water moves in and out of the guard cells by osmosis
  • The amount of turgor pressure within plant cells allows them to remain rigid
  • As the number of water molecules present increase in the guard cells this increases the turgor pressure or causes the guard cells to swell and open the stomata
  • As the number of water molecules present decrease in the guard cells causes the guard cells to go limp and close the stomata
• Environmental conditions


  The number of stomata present in a plant is sensitive to environmental conditions
• A plant in dry conditions doesn't want to lose water and therefore will have fewer numbers of stomata
• A plant in humid conditions will have many stomata as excess water loss is not an issue
• If there is a limit on carbon dioxide in the air plants will have more stomata or keep them open for longer to ensure all available CO2(g) is absorbed
• Stomata will only be found on the side of leaves open to the air