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CAIE A Level Biology 9700 · Cell membranes and transport

Cell membranes and transport: describe question

Describe4 marksStandard

A student prepares three agar cubes containing a pH indicator, with side lengths of 1 cm, 2 cm, and 3 cm. The cubes are placed in a solution of hydrochloric acid. The acid diffuses into the cubes from all surfaces, causing the indicator to change colour. The student records the time taken for the colour change to reach the centre of each cube.

Describe how the surface-area-to-volume ratio changes with increasing cube size, and how this affects the time taken for the acid to diffuse to the centre.

0 words · 4 marks

No account needed for your first marks. Your answer is used only to mark it.

How this question is marked

4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.

Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.

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