Catalase – How Do Enzymes Work in Living Tissues?
Classroom Copy
Introduction: What would happen to your cells if they made a poisonous chemical? You might think they
would die. In fact, mammalian cells are always making poisonous chemicals. Amazingly, they do not die
because cells use enzymes to break down these poisonous chemicals into harmless substances.
Enzymes are protein catalysts that speed up the rate of reactions that would otherwise happen more slowly.
There are hundreds of different, yet very specific, enzymes in each of your cells. Each of these enzymes is
responsible for one particular reaction that occurs in the cell. For example, sucrose breaks down sucrose
(disaccharide) into glucose and fructose (monosaccharides). The enzyme sucrase will only react on sucrose. A
substrate is the molecule that the enzyme acts on, and the products are the molecules produced by the reaction.
In this example sucrase is the enzyme, sucrose is the substrate and the products are glucose and fructose.
In this lab, you will study an enzyme found in the cells of many living things. The name of the enzyme is
catalase. Catalase speeds up a reaction which breaks down hydrogen peroxide, a toxic chemical, into 2
harmless substances – water and oxygen. The reaction is as follows: 2 H2O2  2 H2O + O2
The catalase we will use is found in high concentration in liver. Thus, we will use beef liver that has been
frozen. It might be strange to use dead cells to study the function of enzymes. This is possible because when a
cell dies, the enzymes remain intact and active for several weeks, as long as the tissue is kept refrigerated or
frozen.
You must wear safety goggles and aprons at all times during this lab.
Part 1 – Normal Catalase Activity QUESTION: Is Catalase Reusable?
(Note: Be sure to clean the probe and test tubes between steps. DO NOT USE THE PIPETTE EXCEPT TO
PUT THE2 H2O2 INTO THE TEST TUBE.
1. Write a hypothesis about the reuse of catalase on your lab answer sheet.
2. Use forceps to get a piece of liver from Mrs. Thennis. Place this liver into a clean test tube. Push the liver
down into the test tube with a stirring rod.
3. Estimate the rate of the reaction (how rapidly the solution bubbles) on a scale of 0 – 5 (0 = no reaction, 1 =
slow, 5 = very fast). Assume the reaction in step 2 proceeds at a rate of “4” and record the speed on the data
table in the first row.
4. Pour off the liquid from tube 1 into another clean test tube. Add a new piece of liver to the liquid. Record
results as a 0 to 5 reaction rate.
5. Add hydrogen peroxide to the liver remaining in the first test tube. Record results
6. Clean each test tube well.
7. Answer the questions from part 1 the answer sheet and move to part 2.
Note: Reactions that absorbs heat is endothermic; a reaction that gives off heat is exothermic. Feel the
temperature of the test tube with your hand. Is it endothermic or exothermic?
Part 2 – Effect of Temperature on Catalase Activity
QUESTION: How does temperature effect catalase?
1. Write a hypothesis on your lab sheet about how temperature effects catalase.
2. Write an experimental design: independent variable, dependent variable, experimental group, control group
and control variables on your lab answer sheet.
3. Put a piece of liver into the bottom of a clean test tube and cover it with a small amount of water.
4. Place this test tube in a boiling water bath (100o C) for 5 minutes.
5. Use a test tube holderRemove the test tube from the hot water bath, allow it to air cool, then pour out the
water. Add 1 mL of hydrogen peroxide CAUTION: Use a test tube holder when handling the hot test
tubes.
6. Record 0-5 results on in table 2 of your lab worksheet.
7.
Put equal quantities of liver into 3 clean test tubes and one mL of H2O2 into 3 other test tubes. Put one test
tube of liver and one of H2O2 into each of the following water baths: Ice bath (0o C), room temperature
water bath (about 22o C), and a warm water bath (37o C). YOU WILL HAVE A TUBE OF LIVER AND A
TUBE WITH H202 IN EACH OF THE WATER BATHS.
8. After 3 minutes, pour each tube of H2O2 into the corresponding tube of liver and observe the reaction.
9. Record the reaction rates (0 – 5) in Chart 2 of your data sheet.
10. Make a graph of the estimated reaction rate as a function of temperature. You should have 4 points: 0o C
(ice water), room temperature (in degrees Celsius); 37o C (human body temperature) and 100o C (boiling).
Review: An acidic solution has many hydrogen ions (H+) and a pH below 7. An alkaline, or basic solution,
has very few hydrogen ions and a pH above 7. A neutral solution has a pH of 7. Most biological systems
operate at a pH close to neutral.
Part 3 – Effect of pH on Catalase Activity:
QUESTION: HOW DOES PH EFFECT CATALASE
CAUTION: Do not let acids or bases contact your skin or clothing.
1. Write a hypothesis about how pH effects catalase activity on your lab answer sheet..
2. Record independent variable, dependent variable, experimental group, control group and control
variables on your lab worksheet.
3. Label one pH 4, pH 7 and pH 10.
4. Add one piece of liver to each tube.
5. Cover the liver with each of the corresponding pH solutions and soak for 1 minutes.
6. Empty the liquid into the sink.
7. Add H2O2 into each of the test tubes.
8. Record the rates in Table 3 of your data sheet.
9. Make a bar graph of the estimated reaction rate as a function of pH. Be sure to include a title.
Part 4: EXTENSION: Catalase is present in many kinds of living tissues. You will now test for the presence
of catalase in tissues other than liver. Place 2 mL of hydrogen peroxide in each of 4 clean test tubes. To
separate tubes, add a small piece of potato, carrot, liver, and chicken. As you add each test substance, record
the reaction rate (0 – 5) for each test tube in Chart 1 of your data table. (Extra Credit – 5 points) Must include a
hypothesis, experimental design, data table, results summary, and a conclusion (quick research about why
certain foods have greater amounts of catalase)