Osmosis

• Osmosis is a Special Case of Diffusion, That's All
• 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 tiny molecules (like water) to pass through, and bigger molecules (e.g. sucrose) can't
• Water molecules actually pass both ways through the membrane during osmosis
• There are more water molecules on one side than on the other, so there's a steady net flow of water into the region with fewer water molecules, i.e. into the stronger sugar solution
• The strong sugar solution gets more dilute


  The water acts like it's trying to "even up" the concentration either side of the membrane
• Osmosis


  A type of diffusion-passive movement of water particles from an area of higher water concentration to an area of lower water concentration
• Observing the Effect of Sugar Solutions on Plant Tissue

  1. Cut up a potato into identical cylinders

  2. Get beakers with different sugar solutions

  3. Measure the mass of the cylinders

  4. Leave one cylinder in each beaker for 24 hours

  5. Measure the mass of the cylinders again

  6. Calculate the percentage change in mass
• An increase in mass will give a positive percentage change and a decrease will give a negative percentage change
• The dependent variable is the chip mass and the independent variable is the concentration of the sugar solution
• All other variables (volume of solution, temperature, time, type of sugar used, etc.) must be kept the same in each case or the experiment won't be a fair test
• Errors may arise when carrying out the method, e.g. if some potato cylinders were not fully dried or if water evaporated from the beakers
• You can reduce the effect of these errors by repeating the experiment and calculating a mean percentage change at each concentration
• Osmosis is the reason why it's bad to drink seawater when dehydrated