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  • Osmosis
    • What Is It?
      • Type of diffusion
      • Movement of water molecules across a partially permeable membrane.
      • Goes from a high concentration to a low concentration.
    • Partially Permeable Membrane
      • Membrane with very small holes
      • Only let's tiny molecules such as water pass through.
      • Big molecules can't pass through (e.g. Sucrose)
    • What Happens?
      • Water molecules pass both ways through the membrane. This is because they move about randomly all the time.
      • More water molecules on one side so steady net flow of water in to the region with fewer water molecules.
      • The stronger the solution becomes more dilute as the water is trying to "even up" the concentration of the solutions on both sides of the membrane.
    • What Happens In Cells?
      • Tissue fluid surrounds the cells in the body.
      • Tissue fluid will usually have a different  concentration to the fluid inside the cells. This means water will move in to or out of the cell.
      • If the cell is short of water it is more concentrated which means the outside is more dilute so water will go in to the cell.
        • This makes the cell increase in size.
      • If the cell has lots of water it is more dilute which means the outside is more concentrated so water will be drawn out of the cell.
        • This makes the cell decrease in size.
    • Other Information
      • Tissue fluid is water with oxygen, glucose and stuff dissolved in it. It is squeezed out of the blood capillaries to supply the cells with everything they need.
      • An experiment you can do to show osmosis is cut up potato cylinders and measure them and put  some in a beaker of pure water and some in a beaker with a lot of sugar mixed with water. Leave it for about half an hour and measure them again.
        • The one in pure water should have increased in size and the one in the sugar solution should have decreased in size.


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