(iii) What conclusions can be drawn from the
graph about the effect of temperature on
(iv) If you want to store the mixture of
crushed grains and water with minimal
reaction so that it can be used several days
later, what temperature would you choose?
(v) Suggest another method to estimate the
amylase activity for this investigation.
5. A kind of Chinese dessert is made by mixing
milk with ginger juice so that the milk becomes
coagulated. The coagulation of milk is due to
the conversion of a soluble milk protein into an
insoluble form. To find out the conditions for
milk coagulation, a person mixed milk at
different temperatures with some fresh ginger
juice. The mixtures were observed for 15
minutes to see if coagulation would occur. The
results are shown in the table below:
The results of the experiment are shown
(i) Explain why the paper discs rose to the surface
of the solution in some of the tubes. (2 marks)
(1) Work out the rate of reaction from the
value of T for each tube. Tabulate your
(i) Referring to the above results, describe the
effect of milk temperature on the rate of milk
coagulation by ginger juice.
(2) Using the data obtained in (1), plot a
graph on graph paper to show the effect
of pH on catalase activity.
(ii) How would you explain the action of fresh
ginger juice in bringing about the
coagulation of milk? Give evidence to
support your answer.
(1) Based on your graph, estimate the
optimum pH of catalase.
(iii) Milk protein also coagulates at low pH. In
which part of the alimentary canal does this
coagulation occur? Based on your biological
knowledge, suggest why the coagulation of
milk protein can facilitate its digestion in that
part of the alimentary canal.
(2)In order to get a more accurate estimate of
the optimum pH, what further work would
you carry out in this experiment?
(iv)A sample of bean extract was refrigerated
C and then allowed to warm to room
temperature. If the experiment was repeated
using this sample, would the catalase
activity be different from that of the
previous experiment? Explain your answer.
6. The following shows the procedure of an
experiment to study the effect of pH on the
activity of catalase extracted from bean
One day, when Keith and Jane walked past
a fresh fruit juice shop, Keith noticed that
some pears were cut into pieces and stored
in a tank of water before use.
Keith thought that the shopkeeper
stored the cut pears in water in order
to extract more juice. Explain the
Past HKCEE Questions
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