Gas and Solute exchange

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  • Created by: Jo Wells
  • Created on: 07-04-13 11:03
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  • Gas and Solute exchange
    • substances move by DIFFUSION, OSMOSIS and ACTIVE TRANSPORT
    • exchange surfaces are adapted to maximise efficiency
      • have a large surface area
        • = lots of substances can diffuse at once
      • are thin
        • = short distance for substances to diffuse
      • (in animals) are often ventilated
        • = air moves in and out
      • (in animals) have lots of blood vessels
        • = get substances into and out of the blood quickly
    • structure of leaves lets gases diffuse in and out of cells
      • underneath the leaf is covered in holes called stomata
        • which let carbon dioxide diffuse through
        • oxygen and water vapour also diffuse out through the stomata
          • water vapour is lost from all over the leaf, but mainly via the stomata
            • the water vapour evaporates from the cells inside the leaf
              • it then escapes via diffusion as there's a lot of it inside the leaf and less outside
              • evaporation is fastest in hot, dry and windy conditions
        • the size of the stomata is controlled by guard cells
          • these close the stomata if the plant is losing water faster than it's being replaced by the roots
          • without the guard cells the plant would quickly wilt
      • the flattened shape of the leaf increases the area of this exchange surface so it's more effective
      • the walls of the cells inside the leaf form another exchange surface
        • the air spaces inside the leaf increase the area of this surface so there's more chance for CO2 to get into the cells


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