Core practical - Investigating osmosis in potatoes

Scientists investigate the effects of osmosis on living cells.

  • They observe, with a microscope, cells or tissues placed in solutions of different concentration.
  • They also measure changes in cylinders or discs of fresh potato or beetroot. Cylinders will have a larger mass than discs, so scientists will have larger measurements to work with.

The following experiment investigates the effect of different concentrations of sucrose on potato tissue. It could also be carried out using salt solution instead of sucrose.

Aims of the experiment

  • To investigate the effect of a range of sucrose solutions on the mass of potato cylinders.
  • To determine the concentration of the cell sap of potato cells.

Method

curriculum-key-fact
A 1.0 mol dm−3 solution of a substance contains one mole of the substance per dm3.
  1. Prepare a range of sucrose solutions eg 0%, 20%, 40% and 100%.
  2. Set up a series of boiling tubes with each of these solutions. The 0% sucrose solution will act as the control in the experiment. Make sure each tube is labelled with the concentration.
  3. Prepare a blank results table before you begin. Make sure when weighing the potato cylinders, that their masses are not mixed up when recording them. Each cylinder will have a different mass before and after the investigation.
  4. Dry a potato strip using a paper towel. Measure the mass of the potato cylinder.
  5. Place the potato strip into the 0% solution for 20 minutes.
  6. Remove the potato strip, dry it carefully using paper towel. Measure and record the mass of the potato strip.
  7. Repeat for each sucrose concentration.
  8. For each sucrose concentration, repeat the investigation for several potato cylinders. This allows you to check the precision of your results (results that are close together for the same concentration suggest that the results are precise). The potato cylinders might not all behave in the same way. Making a series of repeat experiments means that any anomalous results can be identified and ignored when a mean is calculated.

Risks

  • Make sure that the potato is placed on a ceramic tile when using the cork borer – do not cut the potato cylinders.
  • Care must be taken when using the scalpel.
  • Wear eye protection when using chemical solutions.

Results

This experiment shows the effect of osmosis on plant tissue. The cylinders will decrease or increase in mass if they lose or gain water by osmosis.