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About This Drill
AP Biology — Unit 3 — Enzymes — Drill 9 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
Interpret enzyme activity data across a pH gradient to identify optimal conditions, explain the molecular basis of pH effects on enzyme function, and evaluate how changing conditions alters catalytic efficiency.
Passage
A student investigated the effect of pH on the activity of the enzyme amylase, which catalyzes the breakdown of starch into maltose. Amylase was incubated with starch at 37C for 10 minutes at seven different pH values. Enzyme activity was measured as the percentage of starch hydrolyzed. The experiment was repeated three times; mean values are reported.
Table 1. Mean percent starch hydrolyzed by amylase at varying pH (37C, 10 min).
| pH | % Starch Hydrolyzed |
|---|
| 3.0 | 2 |
| 4.0 | 8 |
| 5.0 | 22 |
| 6.0 | 61 |
| 7.0 | 88 |
| 8.0 | 47 |
| 9.0 | 11 |
A second trial used the same protocol but substituted the protease enzyme pepsin (optimal pH ~2.0) for amylase.
Questions in This Drill
- Based on the data in Table 1, at what pH is amylase activity greatest, and what does this represent?
- Why does amylase activity decrease significantly at pH 3.0 compared to its activity at pH 7.0?
- A second trial used pepsin instead of amylase, with the same starch substrate and the same pH range. Pepsin is a protease with an optimal pH of approximately 2.0. What would the data table most likely show?
- A student proposes that increasing the concentration of amylase at pH 3.0 would restore enzyme activity to levels comparable to pH 7.0. Is this prediction supported by biological reasoning?
- The data show that amylase activity at pH 8.0 (47%) is substantially lower than at pH 7.0 (88%), but substantially higher than at pH 3.0 (2%). What does this pattern suggest about the effect of pH on amylase?