Enzyme Activity in a School Laboratory
Students investigate how temperature affects the activity of catalase from potato. They cut potato cylinders, add them to hydrogen peroxide, and measure the volume of oxygen collected in 60 seconds at 10, 20, 30, 40, 50 and 60 degrees Celsius. One group reports: 10 C: 4 mL; 20 C: 9 mL; 30 C: 16 mL; 40 C: 20 mL; 50 C: 14 mL; 60 C: 2 mL. Another group using the same method reports 40 C: 12 mL. The teacher asks the class to interpret the results and explain the discrepancy.
1. Describe the trend shown by the first group's data and explain it biologically.
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Activity rises from 10 to 40 C, peaks near 40 C, then falls sharply at 50 and 60 C. The rise reflects increasing kinetic energy of enzyme and substrate molecules, so more successful collisions and more product per unit time, up to the optimum. Above the optimum, heat breaks bonds holding the enzyme's tertiary structure, denaturing the active site so substrate no longer fits; activity falls, and at 60 C most enzyme is denatured. The peak at 40 C is the optimum for potato catalase under these conditions.
2. The second group obtained 12 mL at 40 C. Give at least three plausible reasons for the difference and say how the method could be improved.
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Possible reasons: different potato batch or variety with different catalase content; different cylinder size or surface area; different hydrogen peroxide concentration or volume; different time-keeping or gas collection method; temperature not actually held at 40 C (water bath vs. room). Improvements: standardise cylinder mass and surface area, use a fixed peroxide concentration and volume, hold temperature in a water bath with a thermometer, use the same collection apparatus, and repeat each temperature several times and average. The point is that a single reading cannot distinguish biological variation from methodological error.
3. A student concludes 'catalase is destroyed at 60 C'. Is this conclusion supported? Refine it.
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Partly. The low volume at 60 C shows activity is greatly reduced, consistent with denaturation, but 2 mL is not zero, so some activity remains or gas is still being released. Also, the experiment measures activity, not the amount of enzyme present. A better conclusion: at 60 C most catalase has been denatured and activity is greatly reduced compared with the optimum at 40 C. To claim destruction, one would need to show no activity on re-testing at the optimum temperature.