Gas Exchange in Plants

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Gas Exchange in Plants
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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)

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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

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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
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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

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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 GCs

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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

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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

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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

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Lenticels
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Overall

• Gas exchange in plants is completed by diffusion
• No specific organ involved