A-LevelBiologyCell structureFeb/Mar 2023Paper 1 Q21 Mark
A student calibrated an eyepiece graticule using a stage micrometer. • Each division of the stage micrometer was 0.01 mm. • With a ×10 magnification objective lens, 10 eyepiece graticule units matched 10 divisions on the stage micrometer. The same microscope was used with a ×40, instead of a ×10, magnification objective lens to measure the diameter of an alveolus. The diameter of the alveolus was found to be 96 eyepiece graticule units. The eyepiece lens was not changed. What is the best estimate for the diameter of the alveolus?
A0.960 mm
B3.84 mm
C240 μm
D384 µm
✓ Correct Answer
The correct answer is C: 240 μm
📋 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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