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Potato Enzyme Lab
Background Information:
The compound hydrogen peroxide, H2O2, is a by-product of metabolic reactions in most living things. However, hydrogen
peroxide is damaging to delicate molecules inside cells. As a result, nearly all organisms contain the enzyme peroxidase, which
breaks down H2O2 as it is formed. Potatoes are one source of peroxidase. Peroxidase speeds up the breakdown of hydrogen
peroxide into water and gaseous oxygen. This reaction can be detected by observing the oxygen bubbles generated.
Preparation:
Problem:
Does the enzyme peroxidase work in cold temperatures? Does peroxidase work better at higher temperatures?
Does peroxidase work after being frozen or boiled?
Hypothesis:
Make a hypothesis regarding how you think temperature will affect the rate at which the enzyme peroxidase
breaks down hydrogen peroxide. Consider both low and high temperatures.
Hypothesis: I think that boiling the potato at different temperatures will make the rate of reaction of the peroxide….
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I think that cooling the potato at different temperatures will make the rate of reaction of the peroxide….
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Possible Materials:
Thermometer
Ice
Beaker, 400 ml
Hot Plate
Potato slices, ~5mm thick
Kitchen Knife
Waxed paper/ paper towels
3% hydrogen peroxide
Clock or timer
Large tweezers
Name _______________________________________________ Pd. __________________ Date __________________
READ THROUGH ALL THE PROCEDURES AND THEN ANSWER THE PRE-LAB QUESTIONS.
Pre-lab & Procedure Questions:
1. What is your control in this experiment? __________________________________________________
2. How many total slices of potato do you need? _____________________________________________
3. What is the purpose of so many slices of potato? Wouldn’t 3 be enough?
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4. What is the independent variable in the experiment?
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5. What is the purpose of timing the rate of reaction?
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6. What is the substrate in the experiment? What is the enzyme? Which is catalyzing which?
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Procedures:
1. Slice your potato- you will need 21 slices. Please pick a responsible person from your group to slice the potato.
No trips to the nurse please!!
2. While 1 person is slicing your potato, another member(s) of your group should be collecting materials needed
and setting up your lab station.
a. Make sure to cover the desk with paper towels.
b. Set up 1 beaker with water, thermometer, and a hot plate but don’t turn it on until you are ready!
c. You will also need a beaker with water, thermometer, and ice, but don’t get the ice and add it to the
water until you are ready.
d. you will also need large tweezers to get the potato out of the hot water. (DON’T USE YOUR FINGERS!
THE WATER WILL BURN YOU)
WHEN YOU ARE READY TO TEST3. At room temperature, test for peroxidase activity on your potato. Add 2 drops of hydrogen peroxide to 1
potato slice and observe what happens. TIME the reaction time of the peroxide on the potato (you will see a
bubbling, white foam). Repeat this step 2 more times on new potato slices for a total of 3 observations.
NOTE: It is important at this step to test only 1 slice at a time to make sure you have accurate data.
Name _______________________________________________ Pd. __________________ Date __________________
HEATING THE POTATO4. You are going to heat 3 potato slices at a time.
a. Put the potato slices in a small amount of water in a beaker. THEN you are going to heat the beaker
slowly so that the temperature of the water and the temperature of the potato are always the same. Heat the
first three slices to a temperature at least 10 degrees above room temperature.
b. TURN OFF THE HOT PLATE. Record temperature on data sheet, Carefully remove the three slices, pat
slightly dry(just enough to remove any excess water), and drop 2 drops of hydrogen peroxide on each slice and
time EACH slice and record time of reaction. (NOTE: you should each time a different slice of potato!)
c. You are going to repeat steps (a) and (b) but this time heat the water to at least 10 degrees above last
recorded temperature.
d. Repeat steps (a) and (b) but this time heat the water to at least 10 degrees above last recorded
temperature from step (c).
NOTE: You can pick any three temperatures that you want but you have to start with room temperature
water and raise it slowly to the next temperature each time! And each temperature has to be at least 10
degrees Celsius apart.
EXAMPLES:
Slices 1-3 Room Temp
21C
Slices 4-6
(hot)
31C
Slices 7-9
(hot)
45C
Slices 10-12 (hot)
67C
COOLING THE POTATO5. You are now going to cool a potato slice to below room temperature using ice and water in a small beaker.
AGAIN, you are going to cool THREE slices of potato at a time, just like you did when heating the potato.
a. Place three slices of potato into a beaker of water and add a small amount of ice. Wait until the
thermometer stops changing temperatures, record temperature, remove the potato, pat slightly dry.
b. Drop 2 drops of hydrogen peroxide on each slice of potato and record reaction time for each slice.
c. Now add 3 more slices of potato to the ice water. ADD MORE ICE and watch the temperature drop.
Wait until the thermometer stops moving, record temperature, and test all three slices of potato (steps a
& b)
d. Again, add three more slices of potato to the ice water. Add MORE ICE! If you have to pour out some
of the water that is ok but be sure to leave some of the water in the beaker. This allows for an even
distribution of temperature over the potato. Repeat testing steps.
6. Once you have recorded three slices of potato for six different temperatures, clean up your station. Make sure
to wash your beakers and knives, put all materials back where you found them. Potato slices and paper towels
should be thrown away IN THE TRASH.
Name _______________________________________________ Pd. __________________ Date __________________
Slice #
Temperature
1-3
Room Temp.
4-6
(hot)
7-9
(hot)
10-12
(hot)
13-15
(cold)
16-18
(cold)
19-21
(cold)
Conclusion:
Time for reaction to occur.
ON YOUR OWN!! Remember Lab Reports are not a group effort!!
Answer the pre-lab & Procedure Questions. Make sure your data table is fully filled out. You should have a
temperature recorded for each set of slices of potato. Complete post lab questions.
Name _______________________________________________ Pd. __________________ Date __________________
Post Lab Question: (In COMPLETE SENTENCES!)
1. Checking you Hypothesis: Does your data support or reject your hypothesis? Explain your results using information obtained in
class lectures and notes.
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2. Analyzing Data: At what temperature did peroxidase work best? Why? Why didn’t the peroxidase work at all the temperatures?
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3. Identifying variables: What factors did you need to control in your experiment? (Note: there is more than 1!)
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4. Recognizing Cause and Effect: If you have ever used hydrogen peroxide as an antiseptic to treat a cut or scrape, you know that it
foams as soon as it touches an open wound. How can you account for this observation? (Do research on your own!)
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Name _______________________________________________ Pd. __________________ Date __________________