Diffusion and Osmosis

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  • Diffusion and Osmosis
    • Diffusion
      • It is how gas exchange occurs in the lungs and the leaves of plants
      • The movement of molecules from an area where they are in a high concentration to an area where they are in a lower concentration along a concentration gradient
    • Osmosis
      • A special type of diffusion involving the movement of water molecules through a selectively permeable membrane
        • A selectively permeable membrane allows small molecules such as water through but not larger molecules such as sugar
          • Visking tubing is an example of an artificial selectively permeable membrane
          • Cell membranes are selectively permeable
      • Solution
        • Dilute solution - lots of water
        • Concentrated solution - less water
        • If the concentrations of the solutions inside and outside the cell are different - osmosis will occur
      • How osmosis affects living organisms
        • The cell wall prevents the cell taking in too much water
        • the cell can become plasmolysed - the cells lose so much water that the membrane pulls away from the cell wall
      • Osmosis in animals
        • Cells are usually in carefully controlled conditions and they do not take in or lose too much water
        • A red blood cell will shrivel up in a strong sugar solution or burst if placed in pure water

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