Biology 9700 · AS & A Level · Testing for biological molecules
Testing for biological molecules — practice question
Trypsin is an enzyme that catalyses the hydrolysis of casein, which is a protein present in milk.
Milk that contains casein looks cloudy and white. When casein is hydrolysed by trypsin, the milk changes into a clear (transparent), colourless solution.
A student did an experiment to find out how enzyme concentration affects the rate at which trypsin hydrolyses casein.
The student added a solution of trypsin to a milk sample and measured how long it took for the milk to become transparent. The student repeated the experiment using different concentrations of trypsin. All other variables were kept constant.
Fig. 5.1 shows the results from the experiment.
(a(i))[1]
When the concentration of trypsin rises from $2.0\%$ to $4.0\%$, the time taken for the milk to become transparent falls by $48\%$.
Calculate the percentage decrease in the time taken for milk to become transparent when the concentration of trypsin rises from $0.25\%$ to $0.5\%$.
Write your answer to the nearest whole number.
(a(ii))[5]
Explain the patterns shown in Fig. 5.1.
(b(i))[1]
State a reason for the difference in percentage of maximum activity between immobilised trypsin and trypsin free in solution at $25\,^{\circ}\text{C}$.
(b(ii))[2]
Suggest and explain why the percentage of maximum activity of immobilised trypsin at $55\,^{\circ}\text{C}$ is higher than the percentage of maximum activity of trypsin free in solution at $55\,^{\circ}\text{C}$.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “34%” …