Substances are always moving in and out of cells: oxygen into red blood cells, water into root hairs, glucose out of the gut into the blood. GCSE Biology asks you to explain three ways this happens (diffusion, osmosis and active transport) and to use them in unfamiliar examples.
This free quiz mixes recall with the kind of thinking exam questions ask for: comparing concentrations, working out a percentage change in mass and reading a graph from the osmosis practical. Every answer comes with a short explanation, so a wrong answer still teaches you something.
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A potato cylinder has a mass of 2.50 g before it goes into a solution and 2.30 g afterwards. What is the percentage change in mass?
Answer: B, −8.0%
Change in mass = 2.30 g − 2.50 g = −0.20 g. Percentage change = (change ÷ starting mass) × 100 = (−0.20 ÷ 2.50) × 100 = −8.0%. The minus sign shows the potato lost mass.
A piece of potato is left in a very concentrated sugar solution for an hour. What happens to its mass, and why?
Answer: C, It decreases, because water moves out of the potato cells by osmosis
The sugar solution is more concentrated than the cytoplasm and sap inside the potato cells. Water therefore moves out of the cells by osmosis, into the solution, and the potato loses mass.
Diffusion and osmosis are both passive: particles spread out from where they are more concentrated to where they are less concentrated, and the cell spends no energy. Osmosis is simply the special case for water crossing a partially permeable membrane.
Active transport is the odd one out. It moves particles the other way, from a more dilute solution into a more concentrated one, so the cell has to pay for it with energy from respiration. That is why cells that do a lot of active transport, such as root hair cells, have many mitochondria.
Start by comparing the two solutions: which side has more water and less solute? Water moves by osmosis towards the more concentrated solution. Then say what happens to the cell: an animal cell can swell and burst or shrink, while a plant cell becomes turgid or flaccid because its cell wall stops it bursting.
In the practical, always calculate the percentage change in mass rather than comparing raw masses, because the pieces never start at exactly the same mass. Divide the change by the starting mass and multiply by 100, and keep the minus sign when the mass goes down.
It is written to fit all of them. Diffusion, osmosis and active transport appear in the GCSE Biology specifications of all three boards, although the wording and the details of the required practical vary a little between boards. Check your own specification for the exact names your board uses.
Yes. The questions in this set are suitable for both tiers. Higher tier papers ask more application and calculation questions on the same ideas, so the harder questions here are good practice for that.
No. Each attempt picks a set of questions from a larger bank and shuffles the order of the answers, so you cannot learn the answers by position. You can also retry only the questions you missed.
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These practice questions were written by Cloudia Tutoring. They are not official AQA, Pearson Edexcel or OCR material, and Cloudia Tutoring is not affiliated with or endorsed by any exam board or the Department for Education. Always check your own exam board's specification.
Reviewed by Claudia Edwards on 19 October 2026 Last updated .
