Download catalytic activity of enzymes – the liver lab

Name: ________________________________ Date: ________________ Block: _____
The Liver Lab
BIOLOGY
OBJECTIVES:
1. To observe the effect of catalase on the chemical breakdown of hydrogen
peroxide.
2. To observe the effects of temperature and pH, on catalase activity.
BACKGROUND INFORMATION:
Hydrogen peroxide is a highly reactive chemical, often used for bleaching and for
cleaning minor wounds. It is also formed continually as a by-product of chemical reactions in
living cells, but is poisonous, and must be immediately removed or broken down by the cells.
In living cells, hydrogen peroxide is converted into two harmless substances, oxygen and
water.
For nearly every chemical reaction in organisms, enzymes are present which greatly
speed up the rate of the reaction. In this experiment, you will see the effect of an enzyme
called catalase, which speeds up the breakdown of hydrogen peroxide. Catalase can be found
in the liver of chickens and cows. The breakdown of peroxide can be detected by bubbles of
oxygen that are released and by using the glowing splint test for oxygen. You will have an
opportunity to investigate the effect of temperature, and pH on catalase activity.
MATERIALS:
3% hydrogen peroxide (H2O2)
liver
candle
wood splints
acid (HCl, 0.1M)
base (NaOH, 0.1M)
test tube holder
hot water bath
matches
tube
forceps
HYPOTHESIS: How will changing the temperature and pH of an enzyme affect its activity?
__________________________________________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
PROCEDURE - For A Glowing Splint Test:
1. Light the end of a wood splint with a match or lit candle.
2. Gently blow out the flame on the end of the wood splint so that the wood is glowing
orange.
1
3. Place the glowing splint into the test tube to test for the presence of oxygen gas. If the
wood split re-lights, then there is oxygen present. If the wood split does not re-light by
goes out, then oxygen is not present.
PROCEDURE:
Part A: Temperature Test
1. Pour 3% hydrogen peroxide into a test tube to a depth of about one centimeter (the
width of your pinky finger.
2. Liver is an organic material, which contains the enzyme catalase. Pick up a small
piece of fresh liver and drop it into the tube. Place your thumb over the mouth of the
tube and shake gently. Observe the reaction and test with a glowing splint. Record
your results. Rinse your test tube.
3. Place a small piece of boiled liver of the same size you used before in a test tube. Repeat
steps 1 & 2. Record your results. Rinse your test tube.
Part B: Acid Test
4. Pour about one cm of acid (HCl) into a test tube. Pour about one cm of hydrogen
peroxide into the test tube. Use a glowing splint to test for the catalytic activity of the
acid. Record your results. Rinse your test tube.
5. Place a small piece of fresh liver in a test tube. Carefully pour in just enough acid
solution to cover the liver. Let the liver soak in acid for three minutes. After three
minutes, pour the acid into the proper waste beaker and rinse the liver with water a
few times.
6. Repeat steps 1 & 2 using the liver soaked in acid. Record your results. Rinse your test
tube.
Part C: Base Test
7. Pour about one cm of base (NaOH) into a test tube. Pour about one cm of hydrogen
peroxide into the test tube. Test for the catalytic activity of the base with a glowing
splint. Record your results. Rinse your test tube.
8. Place a small piece of fresh liver in a test tube. Carefully pour in just enough base
solution to cover the liver. Let the liver soak in base for three minutes. After three
minutes, pour off the solution into the proper waste container and rinse the liver with
water a few times.
9. Repeat steps 1 & 2 using the liver soaked in base. Record your results. Rinse your test
tube.
Wrap Up
2
10. While you remember the reactions, fill in the fourth column of your data chart,
estimating the relative activity of each catalyst on a scale of 0-10 (0 = no catalytic
activity; 10 = very strong catalytic activity).
11. Carefully clean all the glassware you have used.
DATA:
Record your observations in the chart below. Record the amount of bubbles released,
whether or not the glowing splint indicated the presence of oxygen. (Did it relight? Once?
More?) In the column on the right, estimate of the different rates of catalytic activity, using a
scale of 0 to 10 (0 = no detectable activity; 10 = extremely high activity).
Catalytic Activity of Various Substances
Substance
Activity Measured By
Amount of Bubbling
Lots Some Little None
Amount of
Activity
Rated by
Number
(0-10)
Additional DETAILED
Observations
Glowing Splint Test
Lights!
Nothing
Liver (whole)
Liver (boiled)
Acid
pH=________
Liver soaked in
acid
Base
pH=________
Liver soaked in
3
base
ANALYSIS QUESTIONS:
A. What was the enzyme in this lab?
B. What was the substrate?
C. What were the products?
D. What did the glowing splint test show and how is that related to the enzyme’s
activity?
E. Describe what you saw when fresh liver was placed into hydrogen peroxide.
F. What effect does boiling the liver have on catalase’s activity?
G. What effect does acid have on the catalytic activity of catalase?
H. What effect does base have on the catalytic activity of catalase?
EXTENSION QUESTIONS:
4
I. Why is it important that your body carefully control the temperature and pH of its
tissues?
J. Why was it necessary to test the acid and base for catalytic activity?
5