Introduction
What would happen to your ceils ifthey made a poisonous chemical? You might think that they
would die. In fact, your cells are always making poisonous chemicMs. They do not die because
your ceils use enzymes to break down these poisonous chemicals into harmless subslances.
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 in the ceil.
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 speeds up a reaction which breaks down hydrogen
peroxide, a toxic chemical, into two harmless substances - water and oxygen.
Materials (per group)
safety goggles
small graduated cylinder
3 test tubes
3 hydrion (pH) papers
glass stirring md
0. I M hydrochloric acid
3% hydrogen peroxide
chicken liver (catalase)
forceps
2 small beakers
0.1 M sodium hydroxide
hot plates
ice bath
glass-marking pencil
PROCEDURE
1. Put on safety goggles. CAUTION:. Hydrogen peroxide can be irritating to skin and eyes. If
you spill any on yourself or your clothes, wash it off immediately.. Liver contains the enzyme
catalase, which breaks do~m the hydrogen peroxide formed in cells and bubbles of oxygen gas
are released..
Effect of.p~H on tara|use activity
Using the glass-marking pencil, number the test tubes from I to 3. Using a graduated
cylinder, measure out 2 mL of hydrochloric acid and add it to te~t tube I. CAUTIO~N:
When diluting an acid, &lways pour the acid into the water, Rinse out the gadumed
:cylinder. Put 2 mL of water into teat tube 2. Put 2 mL of sodium hydroxide into
test tube 3. Rinse out the graduated cylinder.
!.sing forceps, add a small piece of liver to each flask and mix well by swirling the flask.
Let iz sit for two minutes.
Using the clean graduated cylinder; add 5 mL of hydrogen peroxide to each flask. Look for
bubbles. Idemif> the amount of activity in each flask by assigning it a number from 0 to 3,
~hen 0 means no bubbles, 1 means few bubbles, and 3 means many bubbles.
6. Record all your observations in the data table on the next page.
Clean out flasks 1.2. and 3. DO NOT THROW LIVER DO\VN THE SINK DIL-~IN.
Effect of temperature on catal~se activity
Using the glass-marking pencil, number three test tubes from l to 3. With a clean medicine
dropper, put 10 drops of water into test tube 1. Add a small piece of liver to it. Place this
test tube in a boiling water bath for five minutes.
Put l 0 drops of water into test ~ube 2. Add a small piece of liver to it. Place this test tube
into an ice water bath for five minutes.
Put 10 drops of water into test tube 3. Add a small piece of liver to it. Place this test tube
into a room-temperature water bath for five minutes.
10. Remove t~t ~b~ L.from boiling water bath with test tube holder and place it in test tube
rack to cool. Remov,, te~t rai~ 2 aacl 3 from their water baths and place them in them
tube rack. Pour offwater from test tubes but leave the liver inside.
11. Using a graduated cylinder, add 2 mL of hydrogen peroxide to each test tube. Look for
bubbles. Identify the amount of activity in each flask by assigning it a number from 0 to 3,
when 0 means no bubbles, 1 means few bubbles, and 3 means many bubbles.
12. Record all your observations in the data table on the next page.
Numb~
I. What happened ~hen hydrogen peroxide was added to each flask (different pH’s)?
2. What happened when hydrogen peroxide was added to each test tube (different temperatures)?
3. In which flask was the bubble activity greatest? What was the pH of the solution?
.4. In which test tube was the-bubble activity greatest? What Was the temperat~e of the solution?
ANALYSIS AND CONCLUSIONS
1..At what pH does catalase function best? How do you know?
2. At what temperature does catalase function best? How do you know?
3. Ifa strong acid has a pH of ha strong base has a pH of 14; and water has a pH of 7 Does cata|ase work best in an acid, base, or neutral environment? Expla n
CRITICAL THINKING AND APPLICATION
1. What does the pH scale meas~e?
2. In the investi~ar.ion above, how can you tell thai: pH a~fec~s the chemical activity of the
en.~..Tne rather than the c~emical activity of the hydrogen peromde?
3. Water is the major component of cells. \~,~at does this tell you about the optimum pH
most en .zyrnes? Explain.
4. The stomach produces hydrochloric acid to help digest iood, How does this affect the pH ol
the stomach? How does the hydrochloric acid help the stomach-digest food?
would happen if cells had no en .zymes?
6. What would happen if cells did not keep internal conditions such as pH constant?
LAB: Catalase
Page 1 of 5
BIOLOGY LAB
CATALASE
Observing an enzyme
INTRODUCTION:
What would happen to yore cells if they made a poisonous chemical? You might
think that they would die. In fact, yore" 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 speeds up a reaction which
breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and
oxygen. The reaction is as follows:
2H202 ....>2H20 + O~
This reaction is important to cells because hydrogen peroxide (H202) 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. You will be using chicken
or beef liver. 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.
PRELAB REVIEW:
Before you begin this lab, review pH. Recall that pH is the measure of the acidity or
alkalinity of a solution. 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.
Recall that the substrate is the molecule that the enzyme acts on, and the products are the
molecules produced by the reaction. Review why enzymes are reusable.
http://www.geocities.com/CapeCanaveral/Hall/1410/lab-B-01 .html?20072
11/2/2007