# Osmosis

• 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.