Osmosis

• Osmosis


  The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
• Partially permeable membrane


  • Has very small holes that only allow water molecules to pass through, but not larger molecules like sucrose
• Osmosis


  1. Water molecules move both ways through the membrane

  2. More water molecules on one side than the other, so there is a net flow of water into the region with fewer water molecules (the stronger sugar solution)

  3. The strong sugar solution gets more dilute as the water acts to "even up" the concentration on both sides of the membrane
• Osmosis


  A type of diffusion - the passive movement of water particles from an area of higher water concentration to an area of lower water concentration
• Experiment to observe the effect of sugar solutions on plant tissue

  1. Cut potato into identical cylinders

  2. Place cylinders in beakers with different sugar solution concentrations (pure water, high concentration, and some in between)

  3. Measure mass of cylinders before and after 24 hours

  4. Cylinders that gained water will have increased in mass, those that lost water will have decreased in mass

  5. Calculate percentage change in mass and plot graphs
• Experiment variables


  • Dependent variable: chip mass
  • Independent variable: concentration of sugar solution
  • Other variables must be kept the same (volume of solution, temperature, time, type of sugar) for a fair test
• Errors may arise in the experiment, e.g. from incomplete drying of cylinders or evaporation of water from beakers. Repeating the experiment and calculating mean percentage change can reduce the effect of these errors.
• Experiment variations


  • Use different salt solutions instead of sugar solutions and observe the effect on potato chip mass