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 is 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 fast its products are formed. In
this laboratory you will use an oxygen (O2) Gas Sensor
and the Vernier LoggerPro data-logging software program
to measure the formation of oxygen. The sensor measures
the amount of oxygen gas produced and plots it on a graph
similar to the one at the left.
After combining an enzyme with hydrogen peroxide
you can measure the oxygen gas (O2) produced to
determine how quickly the reaction proceeds. At the start
of the reaction, the amount of oxygen will be the same as
the air in the room. After a short time, oxygen accumulates
at a rather constant rate. The slope of the curve at this
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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. 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
LoggerPro software and the oxygen (O2) gas 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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Materials
computer
Vernier computer interface
LoggerPro software
Vernier O2 gas sensor
10 mL graduated cylinder
250 mL Naglene bottle
distilled water
1.5% H2O2 solution
enzyme sources
dropper
three 18 x 150 mm test tubes
test tube rack
stopwatch
Optional Items
warming plates
ice bath
thermometer
test tube holders
pH buffers
etc.
Skill Builder Procedure
1. Obtain and wear goggles.
2. Connect the Oxygen Gas Sensor to the computer interface.
3. Prepare the computer for data collection. Click on the LoggerPro 3.8 icon on the desktop 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 “06A Enzyme (O2)”
4. Place three test tubes in a rack and label them 1, 2, and 3. Fill the test tube 1 with 6 mL of
distilled water. This will be your control. Fill test tubes 2 and 3 with 6 mL of 1.5% H2O2
each.
5. Begin the enzyme catalyzed reaction.
a. Using a clean dropper, add 5 drops of enzyme suspension to test
tube 1.
b. Begin timing with a stopwatch or clock.
c. Cover the opening of the test tube with a finger and gently invert
the test tube two times.
d. Pour the contents of the test tube into a clean 250 mL
NalgeneTM bottle.
e. Place the O2 Gas Sensor into the bottle as shown in Figure 2.
Figure 2: O2 gas
Gently push the sensor down into the bottle until it stops. The
sensor assembly
sensor is designed to seal the bottle without the need for
unnecessary force.
f. When 30 seconds has passed, Click
to begin data collection.
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6. When data collection has finished, remove the O2 gas sensor from the Nalgene bottle. Rinse
the bottle with water and dry the inside with a paper towel.
7. Move your data to a stored run. To do this, go to the Experiment menu. Choose Store
Latest Run.
8. Repeat steps 5 through 7 for test tubes 2 and 3 with the following changes to part 5a:
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Add 5 drops of the enzyme suspension to test tube 2.
Add 10 drops of the enzyme suspension to test tube 3.
9. 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 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: Trial 1 may not show this.) Using the mouse, select and measure the slope of
this initial straight-line portion of your first stored run on the graph. To do this:
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Click on the line at the bottom left where it just begins to rise.
Drag the dark shaded region to the upper right to the part of the line that begins to level.
Click on the Linear Fit button,
(marked with a line and an ‘R”).
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.
In Data Table 1, record the value of the slope, m, for each of the three runs.
Table 1:
The Effect of an Enzyme on a Chemical Reaction
Trial
Test Tube Contents
1
5 Drops w water
2
5 Drops w H2O2
3
10 Drops w H2O2
Slope, or rate (%/min)
10. To print a graph of “Volume of O2 gas produced vs. Time” showing all three data runs:
a. Label all three curves by choosing Text Annotation from the Insert menu, and typing
“Trial 1” (or “Trial 2”, or “Trial 3”) in the edit box. Then drag each box to a position near
its respective curve. Adjust the position of the arrow head.
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.
11. Answer the Skill Builder Questions on the next page.
Page 5 –Enzyme Concentration
Skill Builder Questions –Answer these questions to check your understanding.
1. Compare the slopes of trial 1 and trial 2. How do you know that the enzymes initiate a chemical
reaction with hydrogen peroxide?
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2. Compare the slopes of trial 2 and trial 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 20 drops of enzyme suspension to 6mL of 1.5%
H2O2? (Give an educated guess for a slope value here.)
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Now that you understand how the Vernier LoggerPro software and the O2 gas sensor work, you will
research, design, and conduct your own experiment. Your teacher will assign you to an experimental
question. Write the question below.
Question
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Hypothesis
If __________________________________________________________________________________,
then ________________________________________________________________________________
because _____________________________________________________________________________.
continued on next page
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Procedure
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continued on next page
Page 7 –Enzyme Concentration
Data & Results
Create a data table that summarizes the results of your experiment. You may also attach a graph to this
packet. Be sure that the lines on the graph are clearly labeled.
Analysis
1. Examine your graphed data or data table. As you changed your variable (i.e. temperature, pH, enzyme
source), what happened to the rate of this chemical reaction? Explain how you know?
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2. Compare your results to other groups. Under what set of conditions does the enzyme that breaks down
H2O2 seem to work best?
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continued on next page
Page 8 –Enzyme Concentration
3. Catalase enzyme is normally produced in a person’s liver.
The liver, shown in Figure 3 to the right, “serves a wide
variety of body functions, including detoxifying blood and
producing bile that aids in digestion.” What might happen to
a person’s liver if they produce a lower-than-normal amount
of catalase enzyme?
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Figure 3: The liver
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4. What errors or inconsistencies might have occurred in your experiment?
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How might this have interfered with your results?
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Conclusion
Do you agree or disagree with your hypothesis? Why or why not?
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References:
“catalase. ” Wikipedia, the Free Encyclopedia. Accessed on November 7, 2004. <http://en.wikipedia.org/wiki/Catalase>
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.