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Gas Exchange in Plants - PowerPoint

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					Gas Exchange in Plants
Reactions that involve gasses
   Photosynthesis
       Occurs in the chloroplast
       Energy produced (glucose)
       Greater volumes of gasses exchanged in
        photosynthesis
   Cellular respiration
       Occurs in the mitochondria
       Energy produced (ATP)
    Where does the diffusion of
      gasses occur?
   Between the environment and the plant
       Diffusion through the stomata
   Within the plant
       Gasses move in and out of the the
        intercellular spaces (spongy tissue)
       Passive transport
Stomata
   Where diffusion of
    gasses occurs
       O2 net movement out
       CO2 net movement in
   Underside of leaves
   Guard cells control
    whether they are open or
    not (to leave them open
    would be inefficient.


    Link to other pictures
Guard Cells (GC)
   Kidney bean shaped
   Take in potassium by active transport –
    stimulated by light on the leaf
       Increases the particles in the cell therefore
        water enters by osmosis and GC swell
        opening the stomata (because outer wall is
        thinner making it bulge out)
       Allow minerals out of GC and thus H2O leaves
        via osmosis and the stomata closes
Close the gates the water is
getting out!
   Why not leave the stomata open?
     For gasses to pass across the cell
      membrane they must be dissolved in
      water
     Thus a film of water must surround the
      GC’s
Why not leave the stomata
open?
  So plants are constantly losing water
  This loss of water is called Transpiration

  Without closing GC the plants would
   become very dehydrated
Sensitivity of Stomata
   Number and appearance depend on
    environment conditions
       Hot, dry climates with low humidity have fewer
        stomata
       High humidity = more stomata
       Low CO2 levels = stomata open
       Normal levels of CO2 = stomata relaxed
Beyond the Leaf
   In the roots and stem gas
    exchange occurs in the
    outer layer of cells
   Lenticels break though
    the bark (on woody
    plants) and allow air to
    diffuse though
   Within the plant diffusion
    is used in the spongy
    tissue
Lenticels
Overall
   Gas exchange in plants is completed by
    diffusion
   No specific organ involved

				
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