Enzyme Lab #3: The Effect of pH on an Enzyme
SWBIC Educational Resources >> Activities & Materials >> Enzyme Unit Plan >> Lab 3
Theory:
An individual enzyme works well only over a small pH range. Although some, like stomach enzymes, work at low pH (pH 1-2) and others work at or near neutrality, enzymes do not tolerate a large pH swing. In this lab, you will investigate pH change on catalase, an enzyme which catalyses the decomposition of hydrogen peroxide into hydrogen gas and oxygen gas.
Materials:
- 1 red potato
- blender
- cheesecloth
- 3% hydrogen peroxide
- white vinegar
- small test tubes
- plastic cups
- 20 ml. graduated cylinder
- masking tape
- pen
- test tube rack
- transfer pipettes
- *optional- pH meter or pH paper
Procedure:
After preparing and filtering a red potato into a plastic cup, as previously described, set up five test tubes in a test tube rack; label them A-E. To each test tube, add 2 ml. hydrogen peroxide and the following:
- 4 drops vinegar
- 1 drop distilled water
- 2 drops vinegar, 2 drops distilled water
- 1 drop vinegar, 3 drops distilled water
- 4 drops distilled water
(At this point the students can take the pH of each test tube with some pH paper or a pH meter or the teacher can explain that the pH of test tube A is less than that of B, B is less than C, C is less than D, and D is less than E because of dilution.)
Now add 2 dropperfuls of catalase to each test tube. After a minute or two, measure the height of the foam produced in each test tube. Record these amounts.
Questions:
- With what vinegar-water mixture or at which pH did the catalase work best? (produce the most foam)
- Where was it least effective?
- Construct a line graph of test tube or pH vs. foam height.
- What does your graph say about the influence of pH on catalase activity? Be as specific as possible.
Conclusion:
Are enzymes equally effective at all pH levels? Explain your answer.
Teachers:
The potato, 3% hydrogen peroxide, 5% white vinegar, cheesecloth, and plastic cups are available at the grocery store and some pH strips in the swimming pool section of a local hardware store.
Developed for SWBIC by John Palmer, Gadsden High School.