Biology 20I Catalase Lab
Name: _____________________________________
Date/s lab was done: ______________________________
Teacher instructions: Read the lab and follow the instructions.
Title: The Effect of Different Concentrations of a Substrate on the Rate
of an Enzymatic Reaction.
I.B. Marking rubric
Conclusion and evaluation
Levels/marks
Aspect 1
Aspect 2
Aspect 3
Concluding
Evaluating procedure(s)
Improving the investigation
Complete/2
States a conclusion, with justification,
based on a reasonable interpretation of
the data.
Evaluates weaknesses and
limitations.
Suggests realistic improvements
in respect of identified
weaknesses and limitations.
Partial/1
States a conclusion based on a
reasonable interpretation of the data.
Identifies some weaknesses and
limitations, but the evaluation is
weak or missing.
Suggests only superficial
improvements.
Not at all/0
States no conclusion or the conclusion
is based on an unreasonable
interpretation of the data.
Identifies irrelevant weaknesses
and limitations.
Suggests unrealistic
improvements.
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BIOLOGY 20
THE EFFECT OF DIFFERENT CONCENTRATIONS OF A
SUBSTRATE ON THE RATE OF AN ENZYMATIC REACTION.
SAFETY NOTES:
1. Hydrogen peroxide can damage your clothes. Rinse any spills with water immediately.
2. Keep hydrogen peroxide out of your eyes.
3. Report any accidents or spills to your teacher.
INTRODUCTION: Enzymes are biological catalysts. They are generally large proteins made up of several
hundred amino acids. Enzymes speed up thousands of chemical reactions that occur in living cells. Enzymes
are highly specific. This means that one form of an enzyme generally works on only one type of reaction.
Thus, there must be many different types of enzymes in a cell to help out the many different reactions.
Although an enzyme may change slightly as it performs its job with a substrate, it returns back to its original
state and can then work on another substrate. Therefore, there needs to be only a small amount of an enzyme
present in any cell which will be used over and over again.
This fact leads us to question how quickly an enzyme can process the substrate. In other words, if more
substrate is added, will the enzyme work more efficiently to complete the reaction?
Actually, several factors are known to affect the action of enzymes: salt concentration, pH, temperature,
enzyme poisons, radiation, the concentration of enzymes, and the concentration of the substrate. This
lab will investigate only how an enzyme is affected by different concentrations of substrate – specifically
what effect different concentrations of a substrate (H2O2) have on an enzyme (catalase in potato juice).
Catalase accelerates the breakdown of hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2). Catalase
is found in both plant and animal tissues. It is especially abundant in plant storage organs such as potatoes
and the fleshy parts of fruits.
Hydrogen peroxide is a strong oxidizing agent, which tends to disrupt the delicate balance of cell chemistry.
If too much hydrogen peroxide accumulates, it will kill the cell.
PROBLEM:
MATERIALS: (per group)
PROCEDURES:
100 mL graduated cylinder
60 mL hydrogen peroxide solution
knife
2 pairs of forceps
2 vials
1 glass stirring rod
5 filter paper circles
potato slice
stop watch
paper towels
50 mL beaker
distilled water
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PROCEDURE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Prepare the concentrations of hydrogen peroxide (0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30,
0.35%, 0.40%, 0.45%) according to the instructions in the lab.
Fill the graduated cylinder to the 10 mL mark with the prepared H2O2 and add to a vial.
Lay the potato half on a paper towel and use the knife to cut a slice approximately ½ cm. thick.
Use forceps to pick up just one paper circle and lay it on the potato slice where you see the juice.
Allow the circle to soak in the juice for 5 seconds so that it is completely saturated. Choose only
complete circles.
Using the forceps, move the paper circle to a clean paper towel and allow it to drain for 10
seconds.
Dip the glass stirring rod into the H2O2 solution in the graduated cylinder and then touch it
quickly to the clean paper towel to remove MOST of the liquid. The glass stirring rod should
now be just moist enough to pick up the paper circle by touching the end of the rod to the circle.
Move the circle to the vial.
Set the stopwatch to zero.
QUICKLY BUT GENTLY push the paper circle to the bottom of the vial with the glass rod and
start the stopwatch.
Note the amount of time from the moment the paper circle reached the bottom of the cylinder
until it rises and reaches the surface of the solution.
Record this time in Table I.
Repeat steps 2 – 10, for all your trials. Be sure to use fresh H2O2 solution and a new paper circle
for each trial.
Find the average of the five trials and record it in Table II.
Gather the average times for each concentration of H2O2 from the other groups and record in
Table II.
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PREDICTION:
Indicate a reasonable prediction of a graph of the data. Ensure that the graph is complete.
Rate of reaction
/sec
0 0.05
0.10 0.15 0.20 0.25 0.30
Concentration of the Substrate
(% of H2O2)
OBSERVATIONS:
Data:
Table I: ____________ % H2O2
Times Recorded for Reaction – throw out any “bad” data
Trial
Time (seconds)
1
2
3
4
5
6
7
8
9
10
Avg. Time
Table II: Group Data: Average Times
Concentration of
Time (seconds)
Substrate (%)
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
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Avg.
0.35
0.40
0.45
ANALYSIS: Prepare a properly labeled and titled graph.
ANALYSIS QUESTIONS:
1.
Using your knowledge of the reactants and products, explain why the paper circle floats to the
surface.
2.
What is the relationship between substrate concentration and time of the reaction as shown by the
data? How does this compare with your hypothesis?
3.
What effect do you think catalase enzyme would have on a different substrate such as starch?
Explain.
4.
Form a hypothesis as to why catalase is found in potato cells.
5.
Studying the graph of the reaction, estimate the time in which the reaction will occur if the
concentration of the hydrogen peroxide is 1%.
Conclusion and Evaluation:
On a separate page prepare a complete Conclusion and Evaluation according to your Process
Skills Sheet.
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