Reading a Graph of Enzyme Activity vs. Temperature with Missing Error Bars
A student measures the activity of an enzyme at 10, 20, 30, 40, and 50 °C. Activity rises from 5 to 30 units between 10 and 30 °C, peaks at 30 °C, then falls to 20 units at 40 °C and 4 units at 50 °C. She ran each temperature once. A classmate ran the same protocol and got values within about 3 units of hers at 10, 20, and 40 °C, but at 30 °C the classmate got 24 units and at 50 °C got 9 units. The student's graph has no error bars. She concludes the optimum is exactly 30 °C and that the enzyme is nearly inactive at 50 °C.
1. Assess the claim that the optimum is 'exactly 30 °C.'
Read the worked answer
The data only test 10-degree intervals, so the true optimum could lie anywhere between roughly 20 and 40 °C; the peak is bracketed, not pinpointed. The classmate's 24 units at 30 °C versus the student's 30 units shows substantial variability without replicates, so the peak value is uncertain. To claim an exact optimum, the student would need finer temperature intervals (e.g., every 2–5 °C) and replicates with error bars. The correct statement is that activity is highest among the tested temperatures at 30 °C.
2. Evaluate the claim that the enzyme is 'nearly inactive at 50 °C,' given the two students' results.
Read the worked answer
The claim is uncertain. The student got 4 units and the classmate got 9 units at 50 °C-a more than twofold difference. Without replicates, the uncertainty is unknown. Both values are lower than the peak, but 'nearly inactive' depends on the baseline and measurement noise. A defensible statement is that activity at 50 °C is much lower than at 30 °C in both trials, but the exact level is uncertain. Replicates and a zero-activity control would be needed to support 'nearly inactive.'