Exchange Surfaces

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  • Exchange Surfaces
    • Living cells need oxygen and nutrients to survive, and removal of waste to avoid toxicity
    • Features of a good exchange surface
      • Large surface area
        • provides more space for molecules to move through = increased rate of diffusion
        • E.G root hair cells
      • Thin layer
        • E.G alveoli
        • Reduces the diffusion distance to increase the rate of diffusion
        • (barrier must be permeable)
      • Good blood supply/ventilation
        • Maintains steep concentration gradient so rate of diffusion is high
        • E.G gills
    • Factors that affect the need for an exchange system
      • Size
        • Small organisms (amoeba): cytoplasm close to external environment - diffusion is sufficient
        • Large organisms: several layers of cells - longer diffusion pathway, so diffusion is too slow to be sufficient
      • SA:V ratio
        • Small organisms: large SA:V ratio - area is large enough to supply all cells with sufficient O2
        • Large organisms: small SA:V ratio - area not large enough to supply all cells
      • Level of activity
        • Larger organisms (mammals, warm blooded) need more energy for their more active metabolism, and therefore more O2
  • the need for specialised exchange surfaces To include surface area to volume ratio (SA:V), metabolic activity, single-celled and multicellular organisms.  (b) the features of an efficient exchange surface To include, • increased surface area – root hair cells • thin layer – alveoli • good blood supply/ventilation to maintain gradient – gills/alveolus


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