(AQA GCSE B3.1.1) Osmosis

An overview of osmosis for the AQA B3 spec including examples. 

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  • Created by: Em
  • Created on: 16-04-13 16:06
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  • Osmosis
    • Partially permeable membrane
      • Smaller particles can fit through the membrane, the larger particles cannot
    • THE DIFFUSION OF WATER FROM A MORE CONCENTRATED SOLUTION THROUGH A PARTIALLY PERMEABLE MEMBRANE
    • Examples
      • Plant cells
        • In a concentrated solution, water moves out but due to the thick cell wall it does not collapse fully, but wilting plants are due to this.
        • In a dilute solution, the cell will swell up and become TURGID. It won't burst due to the cell wall. This helps keep plants supported and upright since they are packed full.
      • Red blood cells
      • Experiments
        • Concentrated solution with red food dye in a visking tube (partially permeable membrane), placed in distilled water (pure water).
          • Over time the water moves in and the red food colouring moves up the tube.
        • Cut up pieces of potato and add to test tubes. Add different concentrations of sucrose solution (distilled water  - 0.3m).
          • The mass before and after can then be calculated and the mean change in mass can be calculated.
            • Some will gain mass i.e. +0.5g some will lose i.e. -0.5g.  This can be plotted onto a graph and the point where the line meets the x axis shows the concentration inside the cell because the two concentrations are even and osmosis is not occurring.

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