CAPE BIOLOGY - UNIT 1
Title: Investigating the Effect of Substrate Concentration on Enzyme Activity
Aim: To investigate the effect of hydrogen
peroxide (H2O2) substrate concentration on the
activity of the enzyme catalase.
The progress of an enzyme catalysed reaction can be
followed by testing for the substrates and/or products.
Whatever experiment you carry out it is probably
best to measure the initial rate of the reaction – that
is, the reaction over a short period of time, say 30
seconds. The rate of reaction declines with time, and
if you measure the rate of reaction over a longer time
than this, the effect of the decline of the reaction rate
becomes confused with the effect of the enzyme or
the substrate concentrations.
Catalase is an enzyme that occurs in many plant and
animal tissues. It breaks down toxic hydrogen
peroxide, formed as a by-product of various
biochemical reactions, into water and oxygen (see
equation below). In this experiment, you will
investigate the ability of potato tissue to catalyse the
decomposition of hydrogen peroxide in different
concentrations.
2H2O2 (l)
2H2O (l)
+
O2
(g)
Hydrogen peroxide
water
+ oxygen
Note: Hydrogen peroxide is corrosive. If any
should come into contact with your skin, wash
immediately under cold water.
Requirements: Razor blade/ knife

Cork borer

Ruler

Forceps

Boiling tube

Rubber bung and delivery tube

Test tube

Beakers

Measuring cylinder

Syringe (5cm³)

Stopclock

Potato tuber

H2O2 solutions (0.5, 1.0, 1.5 and 2.0 mol/dm³)
CAPE UNIT 1 BIOLOGY – ENZYMES 2
Procedure
1. With a cork borer, cut a cylinder of potato tuber
tissue about 1cm in diameter and at least 6cm
long. Slice the cylinder into discs 2mm thick and
place them under water in a Petri dish or beaker.
You would require at least 60 discs.
2. With a syringe, place 10cm³ of 0.5mol.dm³
hydrogen peroxide solution into a boiling tube.
Replace the bung on the boiling tube. Set up a
second tube with tap water at a depth where the
delivery tube would be about 2cm below the
surface of the water.
3. Count out 5 discs, and add all into the boiling
tube at the same time. Replace the bung
immediately, and gently shake the boiling tube to
separate the slices. Wait 10 seconds, and then
count the number of bubbles evolved in 1 minute.
4. Record this value in an appropriate table.
5. Discard the contents of the boiling tube, and rinse
it with cold water. Repeat the procedure using 5
fresh discs each time to obtain two further
readings for this concentration of hydrogen
peroxide.
6. Repeat this procedure using the three other
hydrogen peroxide solutions, taking three
readings each time and recording the results in
the appropriate table columns.
7. Calculate to the nearest whole number the mean
of the three readings for each concentration of
hydrogen peroxide.
Table 1 Number of bubbles evolved per minute from
decomposition of hydrogen peroxide (H2O2).
Bubbles per
minute
Concentration
of
hydrogen
peroxide
solution (mol/dm³)
0.5
1.0
1.5
2.0
Count 1
Count 2
Count 3
Mean count
8. Plot a graph of the average number of bubbles
evolved at different concentrations of hydrogen
peroxide.
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CAPE BIOLOGY - UNIT 1
For Consideration:
1. Identify the enzyme and the substrate in this experiment.
2. Account for the shape of your graph as fully as possible.
3. Theoretically what happens with varying substrate concentration on rate of reaction? What is happening in your
test tube?
4. Suggest explanations for each of the following aspects of the procedure you have carried out:
a. Using 5 discs each time?
b. Using discs rather than a single cylinder of potato tuber?
c. Renewing discs and solutions after each count, instead of taking three counts with each set of discs in
one 10cm³ sample of solution?
5. What additional information could you gain about the reaction if you used twice the number of potato discs in
the 2.0mol/dm³ hydrogen peroxide solution?
6. Suggest two ways by which the design of this investigation could be improved.
Skills to be Assessed: Observation, Recording and Reporting (ORR); Analysis and Interpretation (A&I)
A: Observation, Recording and Reporting
Logical report – named headings and correct content; in order
Method – accurate, clear and correct tense
Use of a table and a graph
Table – correct column headings and title given, drawn with ruler
Count measured in whole numbers and mean calc. correct
Graph – appropriate and stated title and scale
Labelled x axis (conc. of hydrogen peroxide mol/dm³)
Labelled y axis (average number of bubbles per minute)
Points plotted correctly and joined by a straight line
Grammar, spelling and punctuation correct throughout
Discussion – appropriate, relevant to topic, accounts for results
2 marks
2 marks
1 mark
0.5 mark
0.5 mark
0.25 mark
0.25 mark
0.25 mark
0.25 mark
2 marks
2 marks
B: Analysis and Interpretation




Background: 3 marks
Trends of the results: 2 marks
 From the graph – quote values also
Explanation of results: 3 marks
 Theoretically as substrate concentration increases the rate of enzyme catalysed reaction increases up to
a point called Vmax (1)….
 In the experiment carried out, it was observed that the rate of reaction…….This is because
Evaluation of procedure: 2 marks
 In the procedure, 10 discs were used………Discs of potato were preferred to a cylinder of potato…
Discs and substrate solution were renewed each time
 Sources of error – experimental error – due to competence of student
 Improvement of procedure
Conclusion: 2 marks
As the concentration of hydrogen peroxide increased from 0.5 to 2.0 mol/dm³, the rate of the reaction increased
from __ to __ bubbles per minute. There was an increasing rate of reaction, which became constant with Vmax at ___
bubbles per minute.
CAPE UNIT 1 BIOLOGY – ENZYMES 2
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