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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
What this skill means
Place equal potato cylinders in a range of solution concentrations, measure initial and final mass, calculate percentage change, repeat and plot mean percentage change against concentration. Zero change estimates equal water potential.
The potato-cylinder investigation combines variables, percentage change, graph interpretation and osmosis explanation, which makes it one of the most useful Paper 5 and 6 practicals to master.
A controlled method
Cut cylinders of the same potato, length and diameter. Blot and measure initial mass, place them in equal volumes of several sugar or salt concentrations for the same time and at the same temperature, then blot consistently and measure final mass.
Why percentage change is better
Even carefully cut cylinders may start at slightly different masses. Percentage change = (final − initial) ÷ initial × 100 allows fair comparison. Use repeats and mean percentage change for each concentration.
Explain gains and losses
In a solution with higher water potential than the cells, water enters by osmosis and mass increases. In a solution with lower water potential, water leaves and mass decreases. The zero-change concentration estimates the solution with equal water potential to the tissue.
Evaluate the method
Control surface area and source tissue, standardise blotting, use sufficient time, prevent evaporation and use more concentrations around the zero-change point. A cork borer and ruler improve sample consistency.
Use this before submitting your answer
A complete answer is specific enough for another person to repeat or assess.
✓Same potato source, cylinder diameter and length.
✓Same solution volume, time and temperature.
✓Consistent blotting before weighing.
✓Percentage change rather than raw change.
✓Repeats and mean for each concentration.
✓Graph and interpolation of zero change.
Try the skill in a question (2 marks)
A potato cylinder changes from 4.00 g to 4.60 g. Calculate the percentage change in mass.
Show the answer and marking guidance
Change = 4.60 − 4.00 = 0.60 g.
Percentage change = 0.60 ÷ 4.00 × 100 = 15%.
Original practice content written for this site. It is not an official Cambridge question.