Same size, blot dry, weigh again. Then find where the line crosses zero.
Osmosis in potato or carrot tissue is one of the most common IGCSE Biology Paper 6 experiments. Here potato cylinders, all cut with a 10 mm cork borer and trimmed to 30.0 mm, are blotted and weighed, then left for 45 minutes in six sucrose solutions from 0.0 to 1.0 mol per dm³, made by diluting a stock with distilled water. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Past-paper referenceOriginal experiment, wording and figures, written in the style of Cambridge IGCSE Biology 0610 Paper 6 (Alternative to Practical). It is not copied from a past paper. The “what the examiners said” notes are our paraphrase of the Principal Examiner Reports for Teachers.
Practise next: 0610/61 May/June 2023, (Question 2(b): carrot cubes in salt solutions, constant variables, why blot, graph with negative values, percentage change) · official past papers
Practise next: 0610/62 May/June 2025, (Question 1(a): potato discs in salt solutions made by dilution, results table, why use ten discs, a safety precaution) · official past papers
Practise next: 0610/61 October/November 2024, (Question 1: osmosis in dialysis tubing, naming a measuring cylinder, the control, repeats) · official past papers
Examiner reports used: 0610 June 2023 (Paper 61), June 2025 (Papers 61, 62 and 63), November 2024 (Paper 61), March 2023 and March 2024 (Paper 62), with the June 2023 Paper 61, June 2025 Papers 61 and 62 and March 2024 Paper 62 mark schemes.
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What a full-mark diagram shows
Same starting size
Cylinders cut with one cork borer from one potato, skin removed, and trimmed to the same length with a scalpel on a white tile.
Solutions by dilution
Stock and distilled water measured with a measuring cylinder, the two volumes adding up to the same total, the same volume in each labelled beaker.
Blot, weigh, time
Blotted with paper towel and weighed on a balance before and after, every cylinder covered, left for a stated time such as 45 minutes.
Results and graph
A table with units in the headings, percentage change worked out from the initial mass, and a graph read where the line crosses zero change.
Habits the examiner reports keep asking for
Say the mass of the potato cylinders, not just “mass”, when you name the dependent variable.
Blot before every weighing: solution left on the surface adds to the mass. “More reliable” is not an explanation.
Divide by the initial mass when you work out a percentage change, and keep the minus sign for a loss.
State constant variables in full: “the time left in the solution”, not “time”; the initial size, not the size or the initial mass.
Cut on a tile, away from your body. Gloves and “be careful” were not credited as precautions for cutting.