A student uses lipase to model the decay of milk at two temperatures. Fatty acids are produced, causing the pH to fall.
Both mixtures start at pH 8.0. At $20 ∘C\text{ }^{\circ}\text{C} ∘C$, the student records the time to reach pH 7.0. At $40 ∘C\text{ }^{\circ}\text{C} ∘C$, the student records the time to reach pH 6.0.
The student calculates a relative rate as $1 ÷\div÷ time\text{time}time$ for each temperature.
Which judgement is correct?
The comparison is valid because matching the initial pH makes the amount of change identical in both mixtures.
The comparison is valid because taking the reciprocal of time corrects for different amounts of change automatically.
The comparison is invalid because a greater decrease in pH always shows that the enzyme is working more slowly.
The comparison is invalid because the recorded times correspond to different endpoints in the two reaction mixtures.
40 exam-style questions on AQA GCSE Biology 7.2 Organisation of an ecosystem, covering 7.2.1 Levels of organisation, 7.2.2 How materials are cycled, 7.2.3 Decomposition, and 7.2.4 Impact of environmental change (HT only). Each one has a worked solution and a mark scheme showing where the marks go.