1. Enzymes are biological catalysts that change the activation energy of chemical reactions.

(a) Explain the meaning of the terms biological catalyst and activation energy.

Biological catalyst ......................................................................................................

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Activation energy .......................................................................................................

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(4)

(b) The graph below shows the results of an investigation into the effect of enzyme
concentration on the initial rate of this reaction.
 Explain why it is necessary to measure the initial rate of reaction when investigating
the effect of enzyme concentration on the rate of reaction.

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(2)

(c) In this investigation, the substrate concentration was a factor that was kept constant.
Suggest two other factors that should be kept constant. For each factor, state how it
can be kept constant.

Factor 1 .......................................................................................................................

How the factor can be kept constant ...........................................................................

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Factor 2 .......................................................................................................................

How the factor can be kept constant ...........................................................................

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(Total 10 marks)
2. (a) Explain what is meant by each of the following terms.

(i) Allele

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(2)

(ii) Phenotype

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(b) Manx cats have no tails and have the genotype Mm. Cats with normal tails have the
genotype mm. The genotype MM is an example of a lethal genotype and the embryo
with this genotype does not develop.

In the space below, draw a genetic diagram to find the probability that a kitten
produced by crossing two Manx cats will have a normal tail.

(3)
(c) Siamese cats have light-coloured fur, but with dark-coloured faces, ears, tails and
paws. This is due to a temperature-sensitive mutation. As a result of this mutation, the
enzyme responsible for the production of the pigment is easily denatured.

A Siamese cat Suggest an explanation for the distribution of dark-coloured fur in a

Siamese cat.

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(Total 10 marks)
3. The graph below shows the results of an investigation into the effect of substrate
concentration on the initial rate of an enzyme-controlled reaction.

0 .2 0
B C

In itia l 0 .1 5
rate o f
rea ctio n
/ m g of
p ro d u cts s –1
0 .1 0

0 .0 5

0
0 10 20 30 40 50 60
Su b strate co n c en tratio n / m g c m –3

(a) Suggest two conditions, apart from temperature, that should be kept constant in this
investigation.

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(2)

(b) Explain why changes in the substrate concentration cause an increase in the rate of
reaction between points A and B on the graph.

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(2)
(c) Suggest why the curve levels off between points B and C.

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(2)

(d) On the graph on page 6, sketch a curve to show how the results for the investigation
would change if it were repeated at a lower temperature.

Explain any differences between the two curves.

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(3)
(Total 9 marks)
4. The graph below shows the results of an experiment to investigate the effect of amylase
Leave concentration on the rate of starch breakdown.

90

80 –
R ate o f sta rc h
b rea k d o w n 70 –
/ m g m in 1
60 –

50 –

40 –

30 –

20 –

10 –

0–
0 50 100 150 200 250
3
C o n ce n tra tio n o f a m y lase / m g c m

(a) Outline a procedure that could have been used to produce these results.

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(4)
(b) Explain the effect of amylase concentration on the rate of starch breakdown.

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(c) Suggest reasons why the points on the graph do not lie on a straight line.
(3)

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(3)

(d) Cellulase is another enzyme that breaks the bonds between glucose molecules in a
polymer. Explain why adding this enzyme in addition to amylase would have no effect
on the rate of starch breakdown.

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(2)
(Total 12 marks)
5. The enzyme pectinase can be used in the commercial process of peeling oranges. In this
process, the waxy (lipid) surface of the oranges is first removed. The oranges are then
submerged in a solution of pectinase. This enzyme hydrolyses the polysaccharide pectin that
holds the cells in the peel together.

After about 12 hours in the solution of pectinase, the orange peel falls off the oranges leaving
clean segments.

(a) (i) Suggest why the waxy surface of the oranges is removed before they are
submerged in pectinase.

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(2)

(ii) Explain why pectinase does not hydrolyse the cellulose found in the orange peel
cell walls.

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(2)

(b) (i) Suggest why chopping up the oranges could speed up hydrolysis.

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(2)
 (ii) The pectinase shows a small increase in concentration over the 12 hours of the
hydrolysis. Suggest why the concentration of the pectinase increases slightly.

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(2)
(Total 8 marks)

6. Read through the following passage about enzymes, then write on the dotted lines the most
appropriate word or words to complete the passage.

Enzymes can be described as biological .............................................. as they reduce

the .......................................... needed for a metabolic reaction to occur.

The ........................................... combines with the enzyme at a specific region of

the molecule called the ........................................ . The shape of this region can

be altered by a change in pH or ................................................ which will

............................................... the rate of the metabolic reaction.

(Total 6 marks)

7. The diagram below illustrates part of a glycogen molecule.

 C H 2O H C H 2O H C H 2O H C H 2O H C H 2O H C H 2O H

C O H H C O H H C O H H C O H H C O H H C O
H H
H H H H H H
C C C C C C C C C C C C
OH H OH H OH H OH H OH H OH H
HO O O O O O OH
C C C C C C C C C C C C

H OH H OH H OH H OH H OH H OH
(a) State the role of glycogen in the human body.

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(1)

(b) An enzyme is used to break the bonds holding the monomers (glucose molecules)
together.

(i) In the space below draw one of the monomers that would result from this
reaction.

(2)

(ii) Explain why this enzyme will not break the bonds in a protein molecule.

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(3)
 (c) Explain the advantages, to living organisms, of using enzymes in biological reactions.

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(2)
(Total 8 marks)

8. Proteins are chains of amino acids and have a wide range of functions in living organisms.

(a) (i) The diagram below shows part of the general structure of two different amino
acids.

Complete the diagram to show how these two amino acids can be joined
together.

R R
H O
N— C— — C— C
H OH
H H
(1)

(ii) Name the bond that is formed between the two amino acids.

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(1)

(b) Explain how the specific sequence of amino acids in a protein determines its three-
dimensional structure.

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(2)
(c) Enzymes are proteins that speed up chemical reactions within living organisms. The
graph below shows the effect of changing enzyme concentration on the rate of
reaction.

R a te of
re ac tio n

X
E n z y m e co n c en tratio n

(i) Explain why increasing the enzyme concentration above point X on the graph
does not increase the rate of the reaction further.

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(2)
 (ii) Outline the practical procedures that could have been used to obtain the results
shown on the graph.

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(4)
(Total 10 marks)

9. With reference to enzyme activity, explain the meaning of the following terms:

Catalyst ...........................................................................................................................

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Activation energy .............................................................................................................

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(Total 4 marks)
10. (a) Describe the structure of a plant cell wall.

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(3)

(b) An experiment was carried out to determine the effect of two enzymes, enzyme A and
enzyme B, on the yield of apple juice.

An apple was cut into small pieces and blended in a food processor to produce apple
pulp.

Four samples of apple pulp of equal mass were mixed with various combinations of
enzyme A, enzyme B and water, as detailed in the table below. Both enzyme solutions
were at the same concentration.

Sample number Mixture

3 3
1 Apple pulp + 5 cm enzyme A + 5 cm water
3 3
2 Apple pulp + 5 cm enzyme B + 5 cm water
3 3
3 Apple pulp + 5 cm enzyme A + 5 cm enzyme B
3
4 Apple pulp + 10 cm water

The samples were incubated at 30 °C for 15 minutes.

Each sample was then placed in a separate filter funnel and the apple juice collected
into a measuring cylinder. The volumes of the apple juice collected from each sample
are shown in the bar chart below.

40

Vo lu m e o f ap p le ju ice co llected / cm 3
30

20

10

0
1 2 3 4
S a m p le n um b e r

(i) Suggest why the apple pulp incubated with water only (sample 4) yielded some
apple juice.

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(1)
(ii) Describe the effect that enzymes A and B have on the yield of apple juice in
samples 1, 2 and 3.

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(2)

(iii) Suggest how these enzymes increase the yield of apple juice.

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(4)
(Total 10 marks)