Required practical - investigating osmosis

• 2 ways to investigate the effects of osmosis on living cells

  1. Observe (with a microscope), cells or tissues placed in solutions of different concentrations
  2. Measure changes in cylinders or discs of fresh potatoes or beetroot.
• Aims of potato experiment

  • to investigate the effects of a range of sucrose solutions, on the mass of potato cylinders
  • to determine the concentration of the cell sap of potato cells
  • IV = the concentration of the sucrose solutions
  • DV = the change in mass of the potato cylinders
  • CV = the time that each cylinder is left in the sucrose solutions, and the size of each cylinder
• Apparatus

  • boiling tubes
  • beakers
  • distilled water
  • sucrose solution
  • potato cylinders (or potato and cork borer)
  • electronic balance
• Method

  1. Set up 6 boiling tubes, containing same volume of one of the sucrose solutions. Label tubes
  2. Prepare 6 potato cylinders using borer & cut cylinders to same length. Dry each potato cylinder using paper towel to remove excess liquid & record its mass before placing it into one of the tubes
  3. Leave potato cylinders in tubes for 40 mins
  4. Remove each potato cylinder from its tube, gently remove excess liquid from surface of cylinder with paper towel & record its mass
  5. Repeat experiment to obtain multiple values of mass change for each solution. Identify anomalous results & calculate mean
• Risk

  • Make sure that the potato is placed on a ceramic tile when using the cork borer - do not cut the potato cylinders towards your hand
  • Care must be taken when using the scalpel
  • Wear eye protection when using chemical solutions
• • the experiment shows the effects of osmosis on plant tissues
  • the cylinders will decrease or increase in mass if they lose or gain water by osmosis