A-LevelBiologyCell membranes and transportMay/June 2025Paper 1 Q201 Mark
Some agar was coloured pink using a pH indicator. The pink agar was then used to make three agar cubes with different dimensions. [Figure 20.1 (three agar cubes of dimensions 2x2x2 cm, 4x4x4 cm, 5x5x5 cm)] The cubes were placed in a beaker and covered with 0.1 mol dm⁻³ hydrochloric acid. The temperature of the experiment was standardised at 20 °C. Hydrochloric acid diffused into the agar cubes causing the cubes to become colourless. What is the surface area to volume ratio of the agar cube that became colourless in the least amount of time?
A0.33:1
B0.83:1
C1.2:1
D3.0:1
✓ Correct Answer
The correct answer is D: 3.0:1
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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