Using potato tissue
Plant tissue can be placed in solutions with different water potentials and the resulting changes in the tissue measured. Potato cylinders are commonly used for this investigation.
A dilution series of sucrose solutions provides a range of concentrations and therefore a range of water potentials. Several concentrations are needed so that a calibration curve can be produced and the point of no net water movement can be estimated. Distilled water provides the 0 mol dm−3 treatment.
Method
- Prepare a dilution series containing several different sucrose concentrations, including distilled water as the zero-concentration solution.
- Add the same volume of each solution to separate boiling tubes.
- Cut potato cylinders of the same diameter and length.
- Blot each cylinder to remove surface moisture, then record its initial mass. Length may also be recorded.
- Place a potato cylinder into each solution.
- Leave every cylinder immersed for the same fixed period while keeping temperature constant using a water bath.
- Remove the cylinders and blot their surfaces again.
- Measure the final mass and, if required, final length.
Variables
| Variable | In this investigation |
|---|---|
| Independent variable | Sucrose concentration, giving solutions with different water potentials |
| Dependent variable | Change in potato mass; change in length may also be measured |
| Controlled conditions | Potato-cylinder dimensions, volume of solution, immersion time and temperature |