Exchanging Substances

  • Created by: India.02
  • Created on: 12-05-19 11:30
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  • Exchanging Substances
    • Exchange with Environment
      • Organisms take in substances they need and get rid of waste products through diffusion
      • Oxygen and CO2 are transferred between cells and the environment during gas exchange
      • In humans, urea diffuses from cells into the blood plasma for removal from the body by the kidneys
      • The ease of gas exchange depends on the organisms surface area to volume ration (SA : V)
    • Exchange Surfaces
      • In single-celled organisms - gases and substances can diffuse directly into or out of the cell across the cell membrane
        • Large surface area compared to volume so enough substances can be exchanged across the membrane to supply the volume of the cell
      • Multi-cellular organisms have a smaller surface area compared to their volume - not enough substances can diffuse from their outside surface to supply their volume
        • Need an exchange surface for efficient diffusion - structures must allow enough of the necessary substances to pass through
      • Thin membrane so that substances only have a short distance to diffuse
      • Large surface area s lots of a substance can diffuse at once
      • Exchange surfaces in animals have lots of blood vessels to get things in and out of the blood quickly
      • Gas exchange surfaces in animals are often ventilated - air moves in and out
    • SA : V
      • The large the organism, the smaller its surface area compared to its volume


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