Question 1Warm-upFoundation
A potato cylinder goes from 2.0 g to 2.4 g in a sugar solution. Calculate the percentage change in mass.
(final − initial) ÷ initial × 100.
Worked solution
- Change g
Answer:
GCSE & IGCSE biology practice
Osmosis questions and answers
Osmosis is the diffusion of water through a partially permeable membrane, from a dilute solution to a more concentrated one. In the classic practical, potato pieces gain mass in dilute solutions and lose mass in concentrated ones. Percentage change in mass .
15 questions · Foundation tier · Every answer is checked as you type it, with a full worked solution. Updated .
Where osmosis comes up
| GCSE (AQA) | Biology and Combined Science, Foundation and Higher: osmosis, and the required practical on the effect of salt or sugar solutions on plant tissue, using percentage change in mass. |
|---|---|
| Cambridge IGCSE (0610) | Core: water moves into and out of cells by osmosis; investigate the effects on plant tissues of solutions of different concentrations. Supplement: water potential, turgid, flaccid and plasmolysis. |
The method
- Change in mass = final − initial (negative if it lost mass).
- % change = change ÷ initial × 100.
- Gained mass: water moved in (the solution was more dilute than the cells).
- No change: the solution has the same concentration as the cells.
Osmosis questions
Try each one before looking at the hint. If you're stuck, the AI tutor can talk you through it step by step.
Warm-up
Question 2Warm-upFoundation
A potato cylinder goes from 4.0 g to 3.5 g. Calculate the percentage change in mass.
It lost mass, so the answer is negative.
Worked solution
- Change g
Answer:
Question 9Warm-upFoundation
A potato cylinder goes from 3.0 g to 3.3 g. Calculate the percentage change in mass.
Change ÷ starting mass × 100.
Worked solution
- Change g
Answer:
Question 10Warm-upFoundation
A potato cylinder goes from 2.5 g to 2.0 g. Calculate the percentage change in mass.
A loss in mass gives a negative percentage.
Worked solution
- Change g
Answer:
Exam-style
Question 3Exam-styleFoundation
A potato cylinder gains mass in a solution. Which way did the water move?
Water moves from dilute to concentrated.
Worked solution
- A mass gain means water moved in by osmosis, from the more dilute solution into the cells.
Answer: Into the cells: the solution was more dilute than the cell contents
Question 4Exam-styleFoundation
A cylinder goes from 5.0 g to 5.6 g. Calculate the percentage change in mass.
(5.6 − 5.0) ÷ 5.0 × 100.
Worked solution
Answer:
Question 5Exam-styleFoundation
A cylinder goes from 1.6 g to 1.2 g in a concentrated salt solution. Calculate the percentage change in mass.
Divide by the starting mass.
Worked solution
Answer:
Question 6Exam-styleFoundation
Why do students calculate percentage change in mass rather than just the change in mass?
Think about pieces of different sizes.
Worked solution
- A bigger piece would change more in grams; percentage change compares them fairly.
Answer: The pieces start with different masses, so percentages make the results comparable
Question 11Exam-styleFoundation
A cylinder goes from 8.0 g to 7.4 g. Calculate the percentage change in mass.
Divide by the starting mass.
Worked solution
- Change g
Answer:
Question 12Exam-styleFoundation
A red blood cell is placed in pure water. What happens?
Animal cells have no cell wall.
Worked solution
- Water moves into the cell by osmosis, from the dilute solution (pure water) to the more concentrated cytoplasm. With no cell wall, the cell can burst.
Answer: It swells and may burst
Question 13Exam-styleFoundation
A potato cylinder gained 0.6 g, a 15% increase in mass. What was its starting mass?
0.6 g is 15% of the starting mass.
Worked solution
- g
Answer: g
Challenge
Question 7ChallengeFoundation
Potato gained 10% mass in 0.2 mol/dm³ sugar and lost 5% in 0.4 mol/dm³. Assuming a straight line between these, estimate the concentration with no change in mass (to 2 decimal places).
The line falls 15% over 0.2 mol/dm³. How far until it falls 10%?
Worked solution
- From to is of the way from 0.2 to 0.4.
- mol/dm³
Answer: About mol/dm³
Question 8ChallengeFoundation
A plant cell is placed in a very concentrated salt solution. What happens?
Plant cells have a cell wall, so they can't burst.
Worked solution
- Water leaves the cell by osmosis; the cytoplasm shrinks and the membrane pulls away from the wall.
Answer: It loses water by osmosis and becomes plasmolysed
Question 14ChallengeFoundation
A cylinder goes from 4.20 g to 3.78 g in a salt solution. Calculate the percentage change in mass, and say which way water moved.
Loss in mass means water left the cells.
Worked solution
- Change g
- The solution was more concentrated than the cells, so water moved out by osmosis.
Answer: : water moved out of the potato cells
Question 15ChallengeFoundation
In the osmosis practical, why are the potato cylinders blotted dry before they are weighed?
Think about what extra water on the outside would do to the mass.
Worked solution
- Solution left on the surface would add mass that wasn't taken in by the cells, making the result inaccurate.
Answer: To remove surface water
Common mistakes
- Dividing by the final mass instead of the initial mass.
- Losing the minus sign for a mass loss.
- Saying salt or sugar moves (in osmosis it's water).
Stuck on one of these?
The TutorAura AI tutor works through it with you step by step, with the reason for each step, then gives you one like it to try. It checks your working too.
Try the AI tutor freeMore biology questions
Sources
The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:
Practise biology with your own AI tutor
Questions at your level, help when you're stuck, and a plan for your exams. Free for 3 days, no card needed.