Exchange Surfaces

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  • Molecules on the Move - Exchange Surfaces
    • Organisms EXCHANGE SUBSTANCES with their ENVIRONMENT
      • Cells can use DIFFUSION to TAKE IN substances they NEED and GET RID of WASTE PRODUCTS, e.g. OXYGEN and CARBON DIOXIDE are transferred between CELLS and the ENVIRONMENT during GAS EXCHANGE.
        • How EASY it is for an organism to exchange substances with its environment depends on its SURFACE AREA TO VOLUME RATIO
    • Surface area to volume ratios
      • Surface area - outer part of the shapeVolume - Amount of space occupied by an object
    • MULTICELLULAR ORGANISMS need EXCHANGE SURFACES
      • In a SINGLE-CELLED ORGANISM, gases and dissolved subtances can diffuse DIRECTLY INTO or out of the cell across the membrane, because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell.
        • Surface area to volume ratios
          • Surface area - outer part of the shapeVolume - Amount of space occupied by an object
        • MULTICELLULAR ORGANISMS have a SMALLER SURFACE AREA compared to their VOLUME - NOT ENOUGH substances can diffuse from their outside surface to supply their entire volume. This means they need some sort of EXCHANGE SURFACE for efficient diffusion. They have to allow ENOUGH of the necessary substances to pass through.
    • Adaptions of exchange surfaces: Thin membrane so substances only have a short distance to diffuse, Large surface area so lots can diffuse at once, lots of blood vessels to get stuff in and out of blood quickly, gas exchange surfaces are ventilated too-air moves in and out.
      • MULTICELLULAR ORGANISMS have a SMALLER SURFACE AREA compared to their VOLUME - NOT ENOUGH substances can diffuse from their outside surface to supply their entire volume. This means they need some sort of EXCHANGE SURFACE for efficient diffusion. They have to allow ENOUGH of the necessary substances to pass through.
      • Villi provide a big surface area so digested food is absorbed more quickly into the blood, they have thin wall and a very good blood supply for quick absorption
  • Gas exchange happens in the lungs. The job of the lungs is to transfer oxygen to the blood and remove waste carbon dioxide from it, they contain air sacs called alveoli where gas exchange takes place, they are specialised to maximise the diffusion.
    • Large surface area
    • Thin walls
    • Good blood supply
    • Adaptions of exchange surfaces: Thin membrane so substances only have a short distance to diffuse, Large surface area so lots can diffuse at once, lots of blood vessels to get stuff in and out of blood quickly, gas exchange surfaces are ventilated too-air moves in and out.
      • Villi provide a big surface area so digested food is absorbed more quickly into the blood, they have thin wall and a very good blood supply for quick absorption

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