• Created by: Josh13579
  • Created on: 04-04-15 17:51
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  • Gas And Solute Exchange
    • The structure of leaves lets gases diffuse in and out of cells.
      • Carbon dioxide diffuses into the air spaces in the leaf, then it diffuses into cells where photosynthesis happens.
        • The underneath of the leaf is an exchange surface. it is covered in tiny holes called stomata which the carbon dioxide diffuses through.
          • Water (produced by photosynthesis) and water vapour also diffuse out through the stomata.
            • The guard cells (these control the size of the stomata) close the stomata if the plant is losing water faster than it is being replaced by the roots.
              • The flattened shape of the leaf increases the area of the exchange surface so it is more effective.
                • The walls of the cells inside the leafform another exchange surface. The air spaces in side the leaf increase the area of this surface so there is more chance of carbon dioxide to get into the cells.
    • Substances move by Diffusion, Osmosis and active transport.
      • Life processes need gases and other dissolved substances before they can happen.
        • For example, for photosynthesis to happen, carbon dioxide and waterhave to get into plant cells. And for respiration glucose and oxygen both have to get inside cells
          • Waste substances need to move out of the cells. They move to where they need to be by diffusion, osmosis and active transport.
            • In life processes, the gases and dissolved substances have to move through an exchange surface. The exchange surface must allowenough of the necessary substances to pass through.
              • Exchange surfaces are adapted to maximise effectiveness -They are thin, so substances only have a short distance     to travel.     -Large surface area, so lots of a substance can diffuse at           once.
                • Exchnaging substances gets more difficult in bigger, more complex organisms- the place where the substances need to be (or the waste is made) ends up being a long way from exchange surfaces.
  • Water vapour  evapourates from the cells inside the leaf. then it escapes by diffusuion becaus ethere is alot of it inside the leaf and less of it in the air outside. Evapouration is quickest in hot, dry, windy conditions.


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