Osmosis

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  • Osmosis
    • Osmosis is the movement of water molecules across a partially permeable membrane from an area of higher water concentration to a region of lower water concentration.
      • Partially permeable is just one with very small holes in it. So only tiny molecules like water can pass through and bigger molecules e.g. sucrose can't.
        • The water molecules pass both ways during osmosis because they move about randomly all the time.
          • Because there are more water molecules on one side then the other there's a steady net flow.
          • Osmosis is a type of diffusion.
            • Osmosis
              • Osmosis is the movement of water molecules across a partially permeable membrane from an area of higher water concentration to a region of lower water concentration.
                • Partially permeable is just one with very small holes in it. So only tiny molecules like water can pass through and bigger molecules e.g. sucrose can't.
                  • The water molecules pass both ways during osmosis because they move about randomly all the time.
                    • Because there are more water molecules on one side then the other there's a steady net flow.
                    • Osmosis is a type of diffusion.
                • Investigating osmosis using potatoes
                  • Dilute solution
                    • Lots of solvent and not much solute
                  • Concentrated solution
                    • Lots of solute and not much solvent
                    • Hypertonic: more sugar then cell so less free water moleculesHypotonic: has less sugar then the cell so more free molecules. Isotonic: Same sugar as in the cell so same number of free water molecules then the cell.
                  • Cut up potato into identical cylinders, get beakers with different sugar solutions in them. One should be pure and one concentrated.
                  • Measure mass then leave in beaker
                    • Take them out and dry and measure again
                      • If they've drawn in water they'll have increased in mass, if drawn out they'll have decreased in mass. Calculate percentage change and plot graph.
                        • Percentage change = Final value - original value/original value x 100.
                        • Dependent variable - chip massIndependent variable - concentration of sugar solution.Control variables - Volume of solution, temperature, time, type of sugar used must be kept the same or won't be a fair test.
                          • Errors - may occur carrying out method, if some potato wasn't dried the excess water would give a higher mass or if water evaporated from the beakers the concentration of the sugar solutions would change. You can deduce the effect by repeating and calculating a mean percentage change.
      • Investigating osmosis using potatoes
        • Dilute solution
          • Lots of solvent and not much solute
        • Concentrated solution
          • Lots of solute and not much solvent
          • Hypertonic: more sugar then cell so less free water moleculesHypotonic: has less sugar then the cell so more free molecules. Isotonic: Same sugar as in the cell so same number of free water molecules then the cell.
        • Cut up potato into identical cylinders, get beakers with different sugar solutions in them. One should be pure and one concentrated.
        • Measure mass then leave in beaker
          • Take them out and dry and measure again
            • If they've drawn in water they'll have increased in mass, if drawn out they'll have decreased in mass. Calculate percentage change and plot graph.
              • Percentage change = Final value - original value/original value x 100.
              • Dependent variable - chip massIndependent variable - concentration of sugar solution.Control variables - Volume of solution, temperature, time, type of sugar used must be kept the same or won't be a fair test.
                • Errors - may occur carrying out method, if some potato wasn't dried the excess water would give a higher mass or if water evaporated from the beakers the concentration of the sugar solutions would change. You can deduce the effect by repeating and calculating a mean percentage change.

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