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Questions............................................................................................................1
HKALE 1995 Biology Paper I...............................................................................1
HKALE 1996 Biology Paper I...............................................................................2
HKALE 1997 Biology Paper I...............................................................................4
HKALE 1998 Biology Paper I...............................................................................5
HKALE 1999 Biology Paper I B2.........................................................................5
HKALE 1995 Biology Paper I...............................................................................8
HKALE 1996 Biology Paper I.............................................................................10
HKALE 1997 Biology Paper I.............................................................................11
HKALE 1998 Biology Paper I.............................................................................11
Questions
HKALE 1995 Biology Paper IHKALE 1995 Biology Paper I8. (a) An experiment was conducted to investigate the effect of temperature on the
activities of amylases I and II. These enzymes were obtained from the same type
of tissue of vertebrate animals I and II respectively. Similar pH, enzyme
concentration and substrate concentration were used. The experimental data
obtained are recorded in the following table :
Temperature/℃ Time for complete digestion of 1 unit of substrate / minute
Amylase I Amylase II
10 2.0 5.0
15 1.6 3.5
20 1.5 2.5
25 1.6 2.0
30 2.0 1.6
35 4.0 1.4
40 10.0 1.5
(i) Plot a graph to demonstrate the effect of temperature on the activities of
amylases I and II.
(5 marks)
(ii) Explain the results for amylase I. (2 marks)
(iii) What are the optimum temperatures for amylase I and amylase II ? What
thermoregulatory ability would the data for amylase I suggest for vertebrate
animal I ? (2 marks)
(b) The graph below shows the effects of two chemicals, A and B, on the activity of
amylase I. Similar pH, temperature, enzyme concentration and chemical
concentration were used in the experiment.
(i) Compare and contrast the effects of chemical A and chemical B on the
activity of amylase I.
(3 marks)
(ii) Explain how each chemical, A and B, exerts its effect on amylase I. (3 marks)
(Total : 15 marks)
Suggested Solution…
HKALE 1996 Biology Paper IHKALE 1996 Biology Paper I10. (a) A student performed an experiment to monitor the progress of a simple enzyme-
catalysed reaction involving one substrate and one product. He prepared replicate
reaction tubes. In each tube, the concentration of only one reaction component,
either the substrate or product, was measured. The results of three selected tubes
are shown as curves A, B and C below :
(i) Identify which measured component, substrate or product, is represented by
each curve.
(1 marks)
(ii) It was realized that the reaction mixture in one of the three tubes had been
wrongly prepared. This resulted in a different reaction condition.
(1) State which curve represents the result of an error in the preparation.
Give a reason for your choice. Suggest two possible mistakes in the
student's preparation of this reaction mixture. (3 marks)
(2) What evidence shows that the other two curves represent identical
reaction conditions ? (2 marks)
(iii) With reference to curve C,
(1) calculate the rate of enzyme reaction at the 3rd minute, given that 100%
concentration is equivalent to 100 mmoles of the measured component
(Show the readings you take from the graph in your calculation.) ; (2
marks)
(2) compare and explain the difference in enzyme reaction rate at the 3rd
and 15th minute. (2 marks)
(iv) Curve A will finally level off and will not reach 100 %. Explain this
phenomenon. (11 marks)
(b) Explain what is meant by the 'active site' of an enzyme. (1 marks)
Total : 15 marks
Suggested Solution…
HKALE 1997 Biology Paper IHKALE 1997 Biology Paper I2. Compare and contrast the characteristics of competitive and non-competitive inhibitors
on enzyme activity.
(4 marks)
Suggested Solution…
HKALE 1998 Biology Paper IHKALE 1998 Biology Paper I6. Give one application of enzyme and explain its effect. (2 marks)
Suggested Solution…
HKALE 1999 Biology Paper I B2HKALE 1999 Biology Paper I B212. The following reaction is catalysed by the enzyme succinate dehydrogenase :
(a) State three parameters that can be used to determine the rate of this reaction. (3 marks)
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(b) The graph below shows the effect of succinate concentration on the rate of reaction under
optimum pH and temperature :
The curve flattens out at X. Give two explanations for this observation based on the
mechanism of enzymatic reaction. (2 marks)
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(c) Malate and succinate are metabolic intermediates in the Krebs cycle. They have the
following structural formulae :
(i) Suggest what effect malate might have on the rate of reaction catalysed by
succinate dehydrogenase. (1 mark)
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(ii) The positions of malate, succinate and fumarate in the Krebs cycle are shown in the
following flowchart :
Malate can play a role in regulating the rate of reactions in the Krebs cycle. Explain
the possible mechanism by which malate can achieve such a control. (4 marks)
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Total : 10 marks
HKALE 1995 Biology Paper IHKALE 1995 Biology Paper I8. (a) (i) Refer to the graph shown below
- title of graph
- properly scaled and fully labelled X and Y axes with correct units
1- 1 curve labelled or keyed
- correctly plotted points (correct conversion for 1/t) for the 2
curves (1 marks for each curve) (if students plot time VS
temp : title () properly scaled and fully labelled axis with
correct unit ().)
Deduct mark if 1-2 points are plotted wrongly, and if
extra points are shown. No mark if > 2 points are plotted
wrongly.
(Bonus : mark if student can distinguish 'reaction rate' and 'enzyme
activity'. Activities of enzyme can be expressed as arbitrary
unit- of substrate over time, to be indicated on Y axis.)
Effect of temperature on the activities of amylase I and II
(correct conversion for 1/t. For marker's reference in checking accuracy of
points)
Temperature /C Rate of react on 1/t / min-1
Amylase I Amylase II10 0.5 0.215 0.625 0.2920 0.67 0.425 0.625 0.530 0.5 0.62535 0.25 0.7140 0.1 0.67
(Possible Max. 5)
(ii) As temperature increases from 10 C to 20 C, the kinetic
energy () of the molecules increases and there is increased
collision () between enzyme and
1
substrate molecules (to form the enzyme substrate complex
which subsequently breaks down to form the products). As
temperature increases further, the active site of the enzyme is
progressively destroyed / the enzyme undergoes thermal
denaturation (1), and the reaction rate declines.
1
(2)
(iii) The optimum temperature for amylase I is around 20C ()
while that for amylase II is the value shown on the candidates
graph ().
1
It is possible that vertebrate animal I is poikilothermic / cold
blooded animal.
1
(2)
OR
The thermoregulatory ability cannot be deduced owing to
insufficient data.
Deduct mark for spelling
mistake.
(b) (i) Both chemicals A and B inhibit the activity of amylase I.
1
The inhibitory activity of A is competitive / can be overcome
by increasing the substrate concentration but the inhibitory
activity of B is non-competitive / cannot be overcome by
increasing substrate concentration.
2
(3)
OR
Contrast the effect at high substrate concentration (1) and at low
substrate concentration (1).
(ii) Chemical A competes with the substrate for the active site ()
on amylase I and produced inhibitory effect at low substrate
concentration (). Chemical A is structurally similar to the
substrate ().
max. 1
However, when substrate concentration increases, more
substrate molecules are available to compete for the active
site on amylase I.
1
Thus inhibitory effect is overcome at high substrate
concentration.
1
Chemical B binds with enzyme in such a way that it reduces
the catalytic properties of the enzyme.
(Total : 15 marks)
(Possible max. 15 marks)back to top
HKALE 1996 Biology Paper IHKALE 1996 Biology Paper I10. (a) (i) Curve A = product ()
Curve B = product ()
Curve C = substrate ()
(1)
(ii) (1) Curve B () because it indicates a slower rate of reaction ()
when compared to the reaction rates indicated by curves A
and C ()
Possible errors are : (any two, 1mark each)
(1)
- lower enzyme concentration was used / less enzyme
was added
- lower substrate concentration was used / less substrate
was added
- possible contaminant(s) / inhibitor(s) was introduced
into the reaction mixture (any other acceptable answer, do not
accept temperature difference as an answer)
(2)
(3)
(2) The remaining two curves / curves A and C show a
corresponding conversion to the product from the substrate
(1) according to (with respect to) their % concentration changes (1) at
various time points ().
(2)
OR Rate of formation of the product as shown in curve A is the
same as the rate of disappearance of the substrate as shown in curve C
(2) throughout the time points ().
(iii) (1) 8 mmoles min -1(1) N.B. No mark for no unit
Readings (1)
(2)
(2) At 3rd minute : faster rate of enzyme reaction (1) / or at 15th
minute : slower rate of enzyme reaction
(1)
At 3rd minute, substrate concentration is higher () / at 15th
minute, substrate concentration is lower, at 3rd minute
chance of collision between enzyme and substrate molecules is higher
() / at 15th minute chance of collision between enzyme and substrate
molecules is less, at 15th minute rate is limited by product inhibition ().
(1 )
(2)
(iv) The reaction is reversible (). End product effect pushes the
reaction backwards and equilibrium is reached (1)
(1)
(b) It is a special region on the enzyme molecule with a specific
configuration () that can bind with the substrate to form an enzyme - substrate complex (). Reaction occurs at the active site ()
(1)
(Total : 15 marks)
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HKALE 1997 Biology Paper IHKALE 1997 Biology Paper I2. Both lower the activity of enzymes () and their actions are reversible () / no
permanent damage to the enzyme.
1
Competitive inhibitor - inhibitor molecules have similar structure as the
substrate molecule (), compete with the substrate for the active sites on the
enzyme molecule (), inhibition effect overcome by increased substrate
concentration ().
1
Non-competitive inhibitor molecules attack the enzyme molecule not at the
active site (), but changes the conformation of the enzyme () prevents the
active site from catalyzing reactions, inhibition effect not overcome by
increased substrate concentration ().
1
Q2 = 4 marks
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HKALE 1998 Biology Paper IHKALE 1998 Biology Paper I6. meat tenderizer (1)
( accept correct alternatives)
contains protease () which breaks down protein in the meat(), renders the
meat more tender()
(2)
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