Specialised Exchange Systems

  • Created by: Jasmine
  • Created on: 19-02-16 19:38
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  • Specialised Exchange Systems
    • Surface Area to Volume Ratio (SA:V)
      • Smaller organisms have bigger surface area: volume ratios than bigger organisms
    • Specialist Exchange Surfaces
      • Single-celled Organisms
        • Substances can diffuse directly into or out of the cell across the cell surface membrane
        • The diffusion is quick as there is a short distance to travel as they have a very high SA:V
      • Multicellular Organisms
        • Slow for 3 reasons
          • 1) Some cells are deep within the body- big distance to travel
          • 2) Larger animals have a smaller SA:V- cannot exchange enough substances to supply a large volume when the SA is small
          • 3) Multicellular have a higher metabolic rate compared to single-celled so they use O2 and glucose up faster
        • Need specialised exchange surfaces eg alveoli in lungs
    • Special Features of Exchange Surfaces
      • 1) A large SA- increases their efficiency eg root hair cells
        • Roots have a large SA so it increases the rate of absorption of water by osmosis
      • 2) They are thin- decrease distance of travel for exchange- one cell thick eg alveoli
        • Alveolus have a single layer of cells called epithelium- decreases distance for O2 and CO2 to diffuse across- quicker diffusion
      • 3) A good blood supply/ventilation-
        • Alveoli have a large capillary network so each alveolus has their own blood supply- constantly takes O2 and gives CO2- helps maintain the concentration gradient


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