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, your cells are always making poisonous chemicals. Amazingly, they do not die because
your 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.
The enzyme is not altered by the reaction. You have 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
NOTES: On another sheet of paper take notes about enzymes.
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
Hydrogen peroxide (H2O2) is produced as a byproduct of many normal cellular reactions. If the cells did not
break down the hydrogen peroxide, they would be poisoned and die.
In this lab, you will study the catalase found in liver cells. 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.
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. A substrate is the molecule
that the enzyme acts on, and the products are the molecules produced by the reaction.
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 your stirring rod and test tubes between steps).
1. Write a hypothesis about the reuse of catalase on your lab answer sheet.
2. Using forceps, cut a small piece of liver and add it to the test tube. Push it into the hydrogen peroxide with a
stirring rod.
Estimate that 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 B proceeds at a rate of “4” and record the speed on the data
table as the rate at room temperature.
3. Recall that a reaction that absorbs heat is endothermic; a reaction that gives off heat is exothermic. Now,
feel the temperature of the test tube with your hand.
4. Pour off the liquid from tube 1 onto a spot plate with liver. Record results.
5. Add another 2 mL of 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.
Part 2 – Effect of Temperature on Catalase Activity
QUESTION: How does temperature effect catalase?
1. Write a hypothesis on your lab answer 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 distilled water.
4. Place this test tube in a boiling water bath (100o C) for 5 minutes.
5. Remove 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).
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).
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. Add 2 mL of hydrogen peroxide (that has been adjusted to the following pH) to each of 3 clean test
tubes:
Tube 1 – pH 4
Tube 2 – pH 7
Tube 3 – pH 10
4. Add one piece of liver to each tube.
5. Record the rates in Chart 3 of your data sheet.
6. 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 – 3 points)