CAIE A Level Biology 9700 · Cell membranes and transport
A student prepared three agar cubes of side lengths 1 cm, 2 cm, and 3 cm. Each cube contained a pH indicator that changes from blue to yellow in acidic conditions. The cubes were placed in a beaker of hydrochloric acid. The acid diffuses into the cubes and the student recorded the time taken for the indicator to change colour throughout the entire cube. Describe the results the student would expect and explain why this occurs.
5 marks, so the mark scheme is looking for about 5 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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