Unit 1 section 3 Exchange Surfaces

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  • Exchange Surfaces
    • exchange of substances with the environment
      • every organism, whatever its size needs to exchange things with its environment
      • Cells need to take in oxygen and nutrients
      • they also need to excrete waste products like carbon dioxide and urea
      • how easy it is to exchange substances depends on the organisms surface area to volume ratio
    • Specialist exchange organs
      • an organism needs to supply every one of its cells with substances like glucose and oxygen
      • it also needs to remove waste products from every cell to avoid damaging itself
      • single celled organisms exchange substances differently to multicellular organisms
        • Single celled Organisms
          • substances can diffuse directly into or out of the cell across the cell membrane
          • the diffusion rate is quick because of the short distance the susbstance has to travel
          • single celled organisms have a relatively high surface area to volume ratio
        • Multicellular Organisms
          • diffusion across the outer membrane is too slow
            • some cells are deep within the body
            • larger animals have a low surface area to volume ratio


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