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:

  1. 4 drops vinegar
  2. 1 drop distilled water
  3. 2 drops vinegar, 2 drops distilled water
  4. 1 drop vinegar, 3 drops distilled water
  5. 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:

  1. With what vinegar-water mixture or at which pH did the catalase work best? (produce the most foam)
  2. Where was it least effective?
  3. Construct a line graph of test tube or pH vs. foam height.
  4. 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.