Biology – Movement into and out of cells | e-Consult

Control Variable: Ensure all potato cylinders are of the same length and have similar diameter to minimise variations in surface area to volume ratio. Also, ensure the temperature of the solutions is kept constant throughout the experiment.

Method to Estimate Water Potential: The principle used is that water will move from a region of high water potential to a region of low water potential across a semi-permeable membrane (the potato cell membrane). The rate of water movement is directly proportional to the difference in water potential. By measuring the mass change of the potato cylinders in each solution over a fixed time period, we can infer the relative water potentials. A higher mass gain indicates a lower water potential in the potato tissue. The mass change can be calculated by subtracting the initial mass of the potato cylinder from the final mass after the immersion period.

Diagram:

1. Potato cylinders of equal length are cut.
2. The cylinders are weighed and recorded (Initial Mass).
3. The cylinders are immersed in solutions of different water potentials (e.g., 0 MPa, -0.1 MPa, -0.2 MPa) for a fixed time (e.g., 24 hours).
4. After the immersion period, the cylinders are removed and re-weighed (Final Mass).
5. The mass change is calculated for each cylinder.

The water potential of the potato tissue can be estimated by comparing the mass change in each solution. A graph of mass change versus water potential can then be plotted to determine the relationship.