AQA Osmosis Required Practical: GCSE Biology Guide

The AQA osmosis required practical tests whether students can investigate how sugar concentration affects the mass of potato cylinders and explain the results using osmosis. To gain full marks, students need to understand variables, percentage change, graph interpretation and water movement through a partially permeable membrane.

Osmosis is one of the required practicals students should fix before Year 11 because it combines method, calculations, graph skills and explanation. KayScience helps students practise this properly through structured GCSE Science revision.

What the Examiner Expects You to Know

Osmosis is the movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane.

In the GCSE osmosis method, students typically:

• Cut equal-sized potato cylinders

• Measure their initial mass

• Place them in different sugar concentrations

• Leave for a set time

• Remove, dry and reweigh

• Calculate percentage change in mass

Examiners are looking for precision. Simply listing steps is not enough. You must show understanding of control variables and why they matter.

Variables and Calculations (Where Marks Are Lost)

Independent variable: concentration of sugar solution
Dependent variable: change in mass
Control variables: size of potato pieces, volume of solution, temperature, time left in solution

Students often forget to mention drying the potato before reweighing. That costs marks.

Percentage change formula:

Percentage change = ((final mass – initial mass) / initial mass) × 100

In Edexcel and OCR papers, calculation accuracy is assessed strictly. Show full working.

For more core topic coverage, click on Videos and Quizzes at https://www.kayscience.com.

How to Secure Marks on a 6 Mark Question

Most osmosis 6 mark questions ask you to:

• Explain results

• Evaluate the method

• Suggest improvements

A strong answer includes:

• Clear scientific reasoning (water moves by osmosis due to concentration gradient)

• Reference to control variables

• Specific improvements (repeat experiment, calculate mean, use more concentrations)

For structured practice, explore https://www.kayscience.com/exam-questions.

Example GCSE-Style Question

A student investigated osmosis using potato cylinders placed in different sugar solutions. Explain how the results show osmosis has occurred and evaluate the method. (6 marks)

Exam Technique Tip

When evaluating, always link improvements to reliability or validity. For example: “Repeating each concentration and calculating a mean reduces the effect of anomalies and increases reliability.” Generic statements like “make it more accurate” do not gain credit.

For structured support with required practicals and exam technique, see https://www.kayscience.com/tuition-timetable.

Common Osmosis Mistakes That Lose Marks

• • saying “water moves from high to low concentration” without saying water concentration
  • not mentioning partially permeable membrane
  • forgetting percentage change
  • confusing mass gain and mass loss
  • not identifying control variables

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