Exchange Services

  • Created by: Abc312
  • Created on: 18-04-18 20:39
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  • Exchanging Substances
    • Surface area to volume ratio
      • How easy it is for an organism to exchange substances depends on the surface area to volume ratio
        • The bigger an organism the smaller the surface area compared to the volume.
      • A single-celled organism has a large surface area compared to the volume and substances can diffuse directly into the cell.
      • Multi-cellular organisms have a smaller surface area compared to the volume
        • This means specially adapted exchange surfaces are needed for efficient diffusion
    • Alveoli in the lungs
      • The  job of the lungs is to transfer oxygen into the blood and remove carbon dioxide from it.
      • The alveoli are air sacs where gas exchange takes place.
      • They are specialised to maximise diffusion
        • They have a very large surface area
        • A moist lining for dissolving gases
        • Very thin walls for a short diffusion path.
        • A good blood supply
    • Villi in the small intestine
      • The small intestine is covered in millions of villi.
      • They are adapted to absorb digested food quicker.
        • The cell walls are only one cell thick.
        • They have a very good blood supply.
      • The villi increase the surface area of the intestine to increase the surface area to volume ratio and speed up diffusion.
    • Structure of Leaves
      • The stomata are holes on the underside of the leaf.
        • They allow carbon dioxide to diffuse into the leaf.
        • Oxygen and water vapour diffuse out of the stomata
        • The stomata are controlled by guard cells which close the stomata if the plant loses too much water.
          • This stops the plant from wilting and dying.
      • The flat shape of the leaf increases the area.
      • The walls of the cells inside the leaf are also exchange surfaces.
        • The air spaces inside the cell increase the area of the surface so there is more chance for carbon dioxide to get into the cells.
    • Gills in fish
      • Gills are where gas exchange happens in fish
        • Water (containing oxygen) enters the fish through the mouth and passes out through the gills.
          • When this happens the oxygen diffuses from the water into the blood and carbon dioxide goes from the blood to the water.
      • Gills are made from thin plates called gill filaments.
        • This increases the surface area for gas exchange.
        • The gill filaments are covered in lamellae.
          • They increase the surface area even further,
          • They have lots of blood capillaries to speed up diffusion.
          • They have a thin surface layer to minimise the distance that the gases need to diffuse,
          • Blood flows across the lamellae in one direction and water in the opposite direction.
            • This maintains a large concentration gradient.


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