Required Practical: Osmosis (AQA GCSE Biology)

• Aim: To investigate the range of concentrations of salt or sugar solutions on the mass of plant tissue
• You will:
  • Prepare samples of potato and place them in different concentrations of sugar or sodium chloride (salt) solution
  • Make measurements of mass and length of your samples before and after soaking them in solutions
  • Calculate the percentage change in mass of plant tissue
  • Plot, draw and interpret appropriate graphs

• In this practical, you should take care to prepare your samples of potato carefully and record your measurements accurately
• This practical can be carried out with either salt or sucrose solutions of at least five different concentrations
• The length of time that the potato cylinders are left will vary
  • This experiment can be carried out in a water bath at 30℃ in 30 minutes

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You will need to use apparatus appropriately to measure out the volumes of your solutions and record your measurements

• You should measure both the mass and the length of each potato cylinder before and after it has been submerged in solution - these measurements are your dependent variables from which you will calculate the percentage change in mass and length
• The independent variable is the concentration of salt or sucrose solution in mol dm³
• Important control variables are type and volume of solute in solution, temperature, and time

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A positive percentage change in mass indicates that the potato has gained water by osmosis (net movement of water from the solution into the potato) meaning the solution is more dilute, a negative percentage change suggests the opposite