Core practical: osmosis in potatoesSpec 1.16
Potato cells gain or lose water by osmosis depending on the concentration of the solution around them. You can measure this as a change in mass.
- Use a cork borer to cut cylinders from one potato, and trim them to the same length.
- Measure and record the mass of each cylinder.
- Put each cylinder in a different concentration of sugar (or salt) solution, including pure water, using the same volume of solution each time.
- Leave them for the same length of time at the same temperature.
- Remove the cylinders, blot them dry with paper towel and measure their final mass.
- Calculate the percentage change in mass for each cylinder and plot a graph of percentage change against concentration.
| Result | Explanation |
|---|---|
| Mass increases | The solution is more dilute than the cell contents, so water moves into the potato by osmosis |
| Mass decreases | The solution is more concentrated than the cell contents, so water moves out of the potato by osmosis |
| No change in mass | The solution has the same concentration as the cell contents, so there is no net movement of water |
Where the graph line crosses the x-axis (0% change), the concentration of the solution equals the concentration of the potato cell contents. Control the potato, the size of the cylinders, the volume of the solution, the time and the temperature. Repeat the experiment and calculate a mean. Cut on a tile away from your fingers, because cork borers and scalpels are sharp.