Equal enzyme samples are kept at 55 ∘C55\,^{\circ}\mathrm{C}55∘C without substrate. One sample is kept there for two minutes and the other for ten minutes.
Both are then cooled to 30 ∘C30\,^{\circ}\mathrm{C}30∘C and mixed with equal fresh substrate samples. The initial rates are 8 and 2 arbitrary units, respectively.
Which explanation best accounts for the lower rate after ten minutes?
More substrate molecules were used up during the longer heat treatment without substrate.
The enzyme molecules had less kinetic energy when both samples reached the same temperature.
The substrate molecules had less kinetic energy when both samples reached the same temperature.
More enzyme molecules lost their active-site shape during the longer heat treatment.
44 exam-style questions on Edexcel GCSE Biology 1.3 Enzymes, covering 1.3.1 Mechanism of enzyme action, 1.3.2 Denaturation of enzymes, 1.3.3 Factors affecting enzyme activity, and 1.3.4 Measuring energy in food by calorimetry. Each one has a worked solution and a mark scheme showing where the marks go.