Page 1 – Enzyme Concentration
The Effect of Enzymes on Reaction Rate
Group Leader: ____________________
Computer Technician: _____________________
Recorder: ________________________
Materials Technician: ______________________
Problem:
H2O2
How do enzymes work best?
Background
Catalase
Enzymes are special proteins that control most of the
chemical reactions that occur in living organisms. They act as
biological catalysts. A catalyst is a substance that speeds up
or slows down a chemical reaction without being destroyed or
changed during the reaction. One enzyme may catalyze, or
start, thousands of reactions every second.
Enzymes may be affected by many factors. The
temperature, pH, and concentration (amount) of an enzyme
can affect how well the enzyme speeds up a certain reaction.
In this laboratory, you will investigate how enzymes can affect
chemical reactions.
The chemical reaction that you will investigate in this
experiment is the breakdown of hydrogen peroxide (H2O2).
Hydrogen peroxide is toxic to many cells. It is sometimes
created whenever cells use sugars for energy. Many organisms
can breakdown hydrogen peroxide (H2O2) using enzymes. The
enzymes destroy the H2O2 before it can do much damage. The
chemical equation below shows the chemical reaction.
Catalase
H2O
O2
Catalase
Figure 1: Hydrogen peroxide enters the active
site of the enzyme catalase where it is broken
down into water and oxygen.
2 H2O2  2 H2O + O2
This chemical reaction is a decomposition reaction because H2O2 breaks down, or decomposes, into
oxygen and water. While this reaction will occur spontaneously, enzymes increase the rate, or speed, of
the reaction. At least two different enzymes are known to catalyze this reaction: catalase, found in
animals, and peroxidase, found in plants.
It is possible to measure the rate of this chemical
reaction by measuring how quickly its products are
formed. In this laboratory you will use a Gas Pressure
Sensor and the Vernier Logger Pro data-logging software
program to measure the formation of gas, namely oxygen,
from this reaction. The sensor measures the amount of
pressure in a sealed vessel and plots it on a graph similar
to the one at the left.
After combining an enzyme with hydrogen peroxide
you can measure the pressure change in a sealed reaction
chamber to determine how quickly the reaction proceeds.
At the start of the reaction, the pressure in the chamber
will be the same as the pressure in the room. After a short
Page 2 –Enzyme Concentration
time, oxygen accumulates in the chamber at a rather constant rate and the pressure in the sealed chamber
increases. The slope of the curve at this initial time is constant and is called the initial rate. This is the
time during which oxygen is being produced rapidly. As the hydrogen peroxide is destroyed by the
enzyme, less of it is available to react. As this happens, O2 is produced at lower rates. When no more
hydrogen peroxide is left, O2 is no longer produced. Since no more gas is being produced, the pressure
will change little and the graph appears flat at this time.
In this laboratory you will first complete a skill builder in which you will learn how to use the Vernier
Logger Pro software and gas pressure sensor. Next, you will be assigned a question to research with your
laboratory group. Using the equipment provided, your group will design and conduct an experiment to
test your question. Finally, your group will write a laboratory report that summarizes your experiment and
your research findings.
Pre-Lab Questions –Answer these questions to check your understanding.
1. What is an enzyme?
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2. List three factors that can affect how well an enzyme works?
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3. What chemical reaction will you be investigating in this laboratory? What is the reactant? What are
the products?
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4. Why is this reaction important to organisms?
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5. What enzymes catalyze this reaction in organisms?
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6. How will you measure the speed, or rate, of this chemical reaction in this laboratory?
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Page 3 –Enzyme Concentration
Materials
computer
Vernier computer interface
LoggerPro software
Vernier Gas Pressure Sensor
1-hole rubber stopper assembly
10 mL graduated cylinder
1.5% H2O2 solution
enzyme suspension
dropper
four 18 x 150 mm test tubes
test tube rack
distilled water bottle
Optional Items
warming plates
ice bath
thermometer
test tube clamp
pH buffers
Skill Builder Procedure
1. Obtain and wear goggles.
2. Connect the Gas Pressure Sensor to the computer interface.
3. Connect the plastic tubing to the valve on the Gas Pressure Sensor.
4. Prepare the computer for data collection. Open the Logger Pro 3.8.4 program from the
Vernier Software folder of the computer. When the program opens…

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
Go to the “File’ menu.
Open the file Biology with Computers.
Open the file “06B Enzyme (Pressure)”
5. Place three test tubes in a rack and label them ‘Control’, 1, 2, and 3. Fill the Control test tube
with 6 mL of distilled water. This will be your control. Fill test tubes 1, 2, and 3 with 6 mL of
1.5% H2O2 each.
6. Begin the enzyme catalyzed reaction.
a. Using a clean dropper, add 1 drop of enzyme suspension to the control test tube. Be sure
to not let the enzyme fall against the side of the test tube.
b. Stopper the test tube and gently swirl to thoroughly mix the contents.
c. Connect the free-end of the plastic tubing to the connector in the rubber stopper. Twist
gently to lock the tubing in place.
d. Click
to begin data collection. Data collection will end after 3 minutes.
NOTE: If the pressure exceeds 130 kPa, the pressure inside the tube will be too great and the
rubber stopper is likely to pop off. Disconnect the plastic tubing from the Gas Pressure
sensor if the pressure exceeds 130 kPa.
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7. When data collection has finished, disconnect the plastic tubing connector from the rubber
stopper. Remove the rubber stopped from the test tube and discard the contents into the sink.
Rinse the test tube with distilled water and place on the test tube rack to dry.
8. Move your data to a stored run. To do this, go to the Experiment menu. Choose Store
Latest Run.
9. Repeat steps 6 through 8 for test tubes 1, 2, and 3 with the following changes to part 5a:



Add 1 drop of the enzyme suspension to test tube 1.
Add 2 drops of the enzyme suspension to test tube 2.
Add 3 drops of the enzyme suspension to test tube 3.
10. Analyze the three lines that you have stored. In the first trial you did not add any hydrogen
peroxide; therefore, no reaction occurred. The shape of the line can be used for comparison
to trials 1, 2, and 3 to determine what effect the enzyme had on hydrogen peroxide.
Each trial should have an almost straight portion that goes up quickly then levels at some
point. (Note: The control may not show this.) Using the mouse, select and measure the slope
of this initial straight-line portion of each graph. To do this:
a. Click on the line at the bottom left where it just begins to rise.
b. Hold down the mouse button and drag the dark shaded region to the upper right to the
part of the line that appears to no longer increase.
c. Click on the Linear Fit button,
(marked with a line and an ‘R”).
d. Click
and a best-fit line will be shown for each run selected. A floating text box
will show you the slope, m, for each line.
e. In Data Table 1, record the value of the slope, m, for each of the four runs.
Data Table 1:
The Effect of an Enzyme on a Chemical Reaction
Trial
Test Tube Contents
1
1 Drop w water
2
1 Drop w H2O2
3
2 Drops w H2O2
4
3 Drops w H2O2
Slope, or rate (%/min)
11. To print a graph of “Gas Pressure vs. Time” showing all three data runs:
a. Label all three curves by choosing Text Annotation from the Insert menu, and typing
“Control” (or “Trial 1”, or “Trial 2”, etc.) in the edit box. Then drag each box to a
position near its respective curve. Adjust the position of the arrow head.
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b. Print a copy of the graph with all three data sets and the lines of best fit displayed. Enter
your name(s) in the dialogue box before you print the graph. Attach this graph to your
final laboratory report to be handed in.
12. Answer the Skill Builder Questions below.
Skill Builder Questions –Answer these questions to check your understanding.
1. Compare the slopes of the Control and Trial 1. How do you know that the enzymes initiate a chemical
reaction with hydrogen peroxide?
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2. Compare the slopes of Trials 1, 2, and 3. What happens to the rate of the reaction if you add more
enzyme?
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3. Predict the rate of the chemical reaction if you added 4 drops of enzyme suspension to 6mL of 1.5%
H2O2? (Give an educated guess for a slope value here.)
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References:
“catalase. ” Wikipedia, the Free Encyclopedia. Accessed on November 7, 2004. http://en.wikipedia.org/wiki/Catalase ( I know!)
Contolini, N. “An Inquiry Laboratory Activity for Biology” Access Excellence. National Health Museum. Accessed 3 Nov, 2009.
<http://www.accessexcellence.org/AE/AEC/AEF/1994/contolini_inquiry.php>
“liver.” Medline Plus. U.S. National Library of Medicine. 29 Oct. 2009. Accessed 3 Nov. 2009.
<http://www.nlm.nih.gov/medlineplus/ency/imagepages/8850.htm>
Masterman, D. & S. Holman. Biology with Computers, 3rd Ed. Vernier Software & Technology, Beaverton, OR, 2003.