Liver and Let Liver
BACKGROUND
Many organisms can decompose hydrogen peroxide (H2O2) enzymatically. Enzymes are
globular proteins, responsible for most of the chemical activities of living organisms. They act as
catalysts, substances that speed up chemical reactions without being destroyed or altered during
the process. Enzymes are extremely efficient and may be used over and over again. One enzyme
may catalyze thousands of reactions every second.
At the start of the reaction, there is no product, and the concentration is the same as the
atmosphere. After a short time, oxygen accumulates at a rather constant rate. The slope of the
curve at this initial time is constant and is called the initial rate. As the peroxide is destroyed,
less of it is available to react and the O2 is produced at lower rates. When no more peroxide is
left, O2 is no longer produced.
OBJECTIVES

Use a computer and an Oxygen Gas Sensor to measure the production of oxygen gas as
hydrogen peroxide is destroyed by the enzyme catalase at various enzyme concentrations.
 Measure and compare the initial rates of reaction for this enzyme when different
concentrations of enzyme react with H2O2.
HYPOTHESIS
Write a 2-part hypothesis that predicts what you think will happen in this investigation and a
scientific reason.
MATERIALS
computer w/ Logger Pro software
Vernier computer interface - LabPro
Vernier O2 Gas Sensor
250 mL Nalgene bottle
2 pipettes
1.5% H2O2
liver enzyme suspension
10 mL graduated cylinder
clock or stopwatch
LABELED DIAGRAM OF PROCEDURE
to LabPro
O2 Gas Sensor
250 mL Nalgene bottle
H2O2 and liver enzyme suspension
Biology with Computers
6A - 1
Experiment 6A
PROCEDURE
1. Plug in the LabPro to an outlet, then connect the Oxygen Gas Sensor to the LabPro. Connect
the LabPro to a computer and prepare the computer for data collection by opening the file
“06A Enzyme (O2)” from the Biology with Computers folder of Logger Pro. (Macintosh
HDApplicationsLogger Pro 3ExperimentsBiology with Computers)
2. Add 6 mL of 1.5% H2O2 to the 250 mL Nalgene bottle.
3. Using a pipette, add 5 drops of enzyme suspension to the Nalgene bottle.
4. Begin timing with a stopwatch or clock.
5. Place the O2 Gas Sensor into the bottle as shown in the labeled diagram of procedure. Gently
push the sensor down into the bottle until it stops. The sensor is designed to seal the bottle
without the need for unnecessary force.
6. When 30 seconds has passed, Click
to begin data collection.
7. When data collection has finished, remove the O2 gas sensor from the Nalgene bottle. Rinse
the bottle with water and dry with a paper towel. Do not get the gas sensor wet.
8. Move your data to a stored run. To do this, choose Store Latest Run from the Experiment
menu.
9. Repeat steps 2-8 for 10 drops and 20 drops of enzyme suspension.
10. Repeat steps 2-9 three more times for a total of 4 trials. (Actually, you will get data from 3
other groups.)
ANALYZING THE DATA
11. Make sure you save the experiment file, using the naming convention:
period_groupletter_liverlab.cmbl. Create an archive of this file by holding down the Control
key on your keyboard. Send this to your lab partners and also drop an archived copy into the
teacher’s Classes folder for your class period on the staff server in order to receive copies to
be taped into your lab notebook.
12. Using the mouse, select the initial linear region of your data on the graph. Click on the Linear
Fit button, . Click
and a best-fit linear regression line will be shown for each run
selected. In Table 1, record the value of the slope, m, for each of the three solutions. (The
linear regression statistics are displayed in a floating box for each of the data sets.)
13. Label all three curves by choosing Text Annotation from the Insert menu, and typing “5
Drops” (or “10 Drops”, or “20 Drops”) in the edit box. Then drag each box to a position near
its respective curve. Adjust the position of the arrowhead.
14. Determine the rate of reaction for each of the time intervals listed in Table 2 using the
procedure outlined in Step 12. Record the rates for all three data runs in Table 2.
6A - 2
Biology with Computers
Liver and Let Liver
DATA
Table 1: # Drops of Enzyme vs. Slope, or rate
# Drops of
Enzyme
Slope, or rate (%/min)
Trial 1
Trial 2
Trial 3
Trial 4
Average
5
10
20
Table 2: # Drops of Enzyme vs. Rate During Time intervals
# Drops of
Enzyme
Rate During Time Intervals
0-0.5 min
0.5-1.0 min
1.0-1.5 min
1.5-2.0 min
2.0-3.0 min
5
10
20
ANALYSIS
1. How does changing the concentration of enzyme affect the rate of decomposition of H2O2?
2. What do you think will happen to the rate of reaction if one increases the concentration of
enzyme to twenty-five drops? Predict what the rate would be for 25 drops.
3. Explain how the rate changes during the time intervals. When is the reaction rate lowest?
When is the reaction rate highest? Give a possible reason for why the rate changes.
CONCLUSION
Write a conclusion for this investigation. Refer to the yellow Rubric for a Conclusion in your lab
notebook.
PLAN A NEW INVESTIGATION
Choose one of the following new questions and write up an investigative plan. Refer to the green
Rubric for Scoring a New Investigation in your lab notebook.
1. Presumably, at higher concentrations of H2O2, there is a greater chance that an enzyme
molecule might collide with H2O2. If so, the concentration of H2O2 might alter the rate of
oxygen production. How does changing the concentrations of the substrate hydrogen
peroxide affect the rate of enzyme activity?
2. Most organisms have a preferred temperature range in which they survive, and their enzymes
most likely function best within that temperature range. What is the effect of temperature of
the catalase on the rate of reaction?
Biology with Computers
6A - 3
Experiment 6A
3. If the environment of the enzyme is too acidic or too basic, the enzyme may irreversibly
denature, or unravel, until it no longer has the shape necessary for proper functioning. How
do environmental factors such as pH level affect the rate of enzyme-catalyzed reactions?
6A - 4
Biology with Computers