Practise 32 exam-style questions on Osmosis for AQA GCSE Biology. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
32 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
2 marks
In an osmosis graph, the student sees a non-linear curve. State two biological reasons why the plot of percentage mass change vs. sucrose concentration may be non-linear.
Model answer
Cell walls limit swelling causing plateau; variable tissue composition (different cells/tissues) causes non-uniform response; plasmolysis threshold leads to sudden mass loss at certain concentrations.
Explanation
Physical constraints (cell wall) and biological thresholds (plasmolysis, tissue heterogeneity) cause deviations from a straight line.
A student wants to use percentiles to show where an individual potato piece result falls among replicate data. Briefly explain how percentiles help in data interpretation.
Model answer
Percentiles show the relative position of a value within the distribution (e.g. 75th percentile means the value is greater than 75% of results). They show how typical or unusual a result is compared with replicates.
Explanation
Percentiles help assess whether a result is near the middle or extreme of the experimental distribution.
Mark scheme
1 mark
percentiles give relative position within dataset (e.g. % below)
1 mark
indicates how typical/unusual the value is versus replicates
Question 3
3 marks
Calculate the percentile rank (as a percentage) of a potato piece with mass change equal to the median when 11 replicates are ordered. Give the formula and final percentile.
Model answer
Median position for n = 11 is (n+1)/2 = 6th value. Percentile ˜ (rank / n) × 100 = (6 / 11) × 100 ˜ 54.5% (˜55%).
Explanation
Median corresponds to the middle ranked item; percentile formula gives the relative standing as a percent.
Mark scheme
1 mark
median position (n+1)/2 = 6
1 mark
formula percentile = (rank / n) × 100
1 mark
˜54.5% (˜55%)
Allow 54%–55%
Question 4
4 marks
A plant tissue piece has mass 3.20 g before placing in a sucrose solution and 2.88 g after 30 minutes. Calculate the percentage change in mass. Show working. Give your answer to 2 significant figures and state whether the tissue has lost or gained mass.
Model answer
Percentage change = ((2.88 - 3.20) / 3.20) × 100 = (-0.32 / 3.20) × 100 = -10.0% ? -10% (loss). Tissue lost mass by 10.0% (10% loss).
Explanation
Percentage change = (change in mass ÷ original mass) × 100. The negative sign shows a loss; 0.32/3.20 = 0.10 = 10% loss.
Mark scheme
1 mark
correct change in mass calculated (-0.32 g)
Award if subtracts final - initial or initial - final with sign
1 mark
correct percentage calculation (-10.0% or -10%)
Allow 1 or 2 d.p.; final rounding to 2 s.f. required
1 mark
states loss
Must say lost mass or decrease
1 mark
working shown
Shows formula: (change / original) × 100
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