Materials:
Procedure:
1. Cut four cubes of potato approximately 1 cm on each side. Remove the skin from each cube.
2. Cut each cube into four slices.
3. Number small plastic cups 1, 2, 3, and 4 using a permanent marker.
4. Place the four slices of potato into each of the four cups.
5. Cover the potato slices in cup 1 with water.
6. Cover the potato slices in cup 2 with vinegar.
7. Cover the potato slices in cup 3 with 0.1 M NaOH.
8. Cover the potato slices in cup 4 with detergent.
9. Cover the potato slices in cup 5 with soda.
10. Determine the pH of the solution in each cup by holding a piece of pH paper with forceps and dipping it into the liquid. Use a new piece of pH paper for each solution. Record the pH in Table 1.
11.Measure exactly 5 ml of hydrogen peroxide in a graduated cylinder and add it to each container.
12.Observe each container for three minutes before you record your observations in Table 1. You are making qualitative measurements for this activity. Positive (+) indicates that a reaction is observed; negative (-) means that a reaction is not observed.
Observations:
Table 1: Results of a study of the effects of pH on enzyme behavior.
Analysis:
1. Enzymes are reaction specific. That is, they catalyze a specific chemical
reaction. Which lab observations permit you to infer that catalase acted
on the hydrogen peroxide and not on the other solutions that were used
in the lab?
Bubbles did not form when the solutions were added. Bubbles formed
only after the hydrogen peroxide was added.
2. The shape of a protein can be changed by environmental factors such as
pH and temperature. Which laboratory observation permits you to infer
that catalase contains a protein?
The tests at the extreme pH values (acetic acid and sodium hydroxide)
produced negative results while the other tests were positive.
Application of principles
Conclusions:
1. State the pH range in which catalase can decompose hydrogen peroxide.
The damaged cells around the wound release catalase (or some similar
enzyme). The unbroken skin around the wound does not release catalase.
2. What environmental factors affect the rate at which an enzyme
functions?
Since catalase is present at the site of a skin wound, hydrogen peroxide is being decomposed rapidly. Surfaces do not have enzymes and so the
hydrogen peroxide lasts longer and can more effectively kill any bacteria
in the area.
3. How does the protein portion of an enzyme affect the behavior of the enzyme?
Enzyme action is affected by the pH of the environment. The result of the acetic acid test shows that a low pH prevents an enzyme from
functioning.