LAB #3: An Enzyme in Plant and Animal
Tissues
BACKGROUND INFORMATION
Liver and other living tissues contain the enzyme catalase. This enzyme breaks down hydrogen peroxide (H2O2), which is a harmful by-product of cellular respiration if it builds up in cells. In this lab, you will perform reactions with the enzyme catalase.

OBJECTIVES:
1. Investigate the enzyme catalase in various tissues.
2. Measure the effect of changes in temperature on reaction rates of an enzyme-catalyzed reaction in a controlled experiment.

INTRODUCTION:
What would happen to your cells if they made a poisonous chemical? You might think that they would die. In fact, your cells are always making poisonous chemicals. They do not die because your cells use enzymes to break down these poisonous chemicals into harmless substances. Enzymes are proteins 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 enzymes in each of your cells. Each of these enzymes is responsible for one particular reaction that occurs in the cell. In this lab, you will study an enzyme that is found in the cells of many living tissues. The name of the enzyme is catalase (KAT-uh-LAYSS); it speed up a reaction that breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and oxygen.

The reaction is as follows: 2H2O2 à 2H2O + O2
This reaction is important to cells because 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 build up toxic levels of this chemical and potentially die. In this lab, you will study the catalase found in plant and animal cells. It might seem 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.
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MATERIALS:

10 test tubes, test tube rack, hydrogen peroxide solution, forceps, a variety of animal and plant tissues (liver, hotdog, potato, carrot, apple) boiled and unboiled, 2 pieces of paper towel, beaker, medicine dropper.

PROCEDURES/OBSERVATIONS:
1. On the lab cart are slices of various plant and animal tissues. DO NOT
TOUCH the samples at any time with your fingers. Use the appropriate forceps to take a piece of each of the unboiled tissues and place it on a piece of paper toweling. Keep each piece away from the others on the towel, and LABEL the towel for their identification.
2. Use the appropriate forceps to take a piece of each of the boiled tissues and place it on a separate piece of paper toweling. Keep each piece away from the others on the towel, and LABEL the towel for their identification.
3. Take 2 clean test tubes and pour 5 ml of fresh hydrogen peroxide solution into each tube.
(CAUTION: Hydrogen peroxide, if spilled on clothing, will produce discoloration).
4. Select an unboiled and a boiled sample of the same tissue. With CLEAN forceps place one of them in each tube. Observe and record the results in DATA TABLE #1.
5. Empty the tubes (DO NOT ALLOW ANY FOOD DOWN THE SINK DRAIN!), rinse them, and again pour 5 ml of fresh hydrogen peroxide into each test tube. Proceed as before with another tissue pair. Record your results in DATA TABLE #1. Continue in this manner until you have tested all tissue pairs and recorded the rest of your results in DATA TABLE #1.

Analysis & Conclusions:
1. How did each sample tissue you tested indicate the presence or absence of catalase in the tissue? ______________________________________________________________________________
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2. Which of the tissues is most active in catalase activity? ______________________________

3. Which of the tissues is least active in catalase activity? Why do you think this is so?
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4. What does your data indicate about catalase activity in boiled and unboiled tissues?
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5. Hydrogen peroxide is frequently used as an antiseptic. When poured on an open wound, hydrogen peroxide begins to bubble. What does this indicate to you about human tissues?
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5. In the terms of a lock and key explain how the enzyme catalase works and why the key appears broken in boiled tissue.
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DATA TABLE #1 - AN ENZYME IN PLANT AND ANIMAL TISSUES

SAMPLE

PLANT or ANIMAL

UNBOILED or BOILED

OBSERVATIONS
ON A SCALE
(0 – 5)

CATALASE
(Yes/No)

LIVER
LIVER
HOT DOG

HOT DOG

CARROT

CARROT

POTATO

POTATO

APPLE

APPLE

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