Core practical: osmosis in potatoes

Key concepts in biology · Transport in cells · note 4 of 5

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Core practical: osmosis in potatoesSpec 1.16

In short

In this core practical, potato cylinders are weighed, left in different concentrations of sugar or salt solution, then blotted dry and weighed again. A gain in mass means water moved in by osmosis because the solution was more dilute than the cell contents; a loss means it was more concentrated. Where the graph crosses 0% change, the concentrations are equal.

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.

Core practical:

Blot each cylinder dry before you weigh it. Wet cylinders have extra mass that is not from osmosis.

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.

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

How does osmosis differ from diffusion?

Osmosis is the diffusion of water only, through a partially permeable membrane, from a dilute solution to a more concentrated solution. Diffusion is the net movement of any particles, such as oxygen or carbon dioxide, from a higher to a lower concentration. Both are passive processes, so neither needs energy from respiration.

Why does osmosis not require energy?

Osmosis does not require energy because it is a passive process. Water diffuses from a dilute solution to a more concentrated solution through a partially permeable membrane, so no energy from respiration is needed. Active transport is different: it moves substances against a concentration gradient, so it does need energy from respiration.

Why is active transport important in root hair cells?

Active transport lets root hair cells take in mineral ions from the soil even when the concentration of ions is higher inside the cell than in the soil. This movement is against the concentration gradient, so diffusion cannot do it. Active transport uses energy from respiration to move the ions into the cell.

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