Question 19M.3.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.HL.TZ1.b |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Lipase was extracted from the fungus Aspergillus niger and used to hydrolyse one of its substrates. This was repeated for an immobilized form of lipase. The graph shows how the enzyme activity varied at different pH and temperature levels.
[Source: adapted from Zdarta, J.; Klapiszewski, Ł.; Wysokowski, M.; Norman, M.; Kołodziejczak-Radzimska, A.; Moszyński, D.;
Ehrlich, H.; Maciejewski, H.; Stelling, A.L.; Jesionowski, T. Chitin-Lignin Material as a Novel Matrix for Enzyme Immobilization.
Mar. Drugs 2015, 13, 2424–2446.]
The graph of the effect of pH on immobilized lipase activity does not allow for the determination of optimum pH precisely. Explain how a more exact value for the optimum pH could be determined.
[2]
a. the experiment is repeated with smaller increments of pH ✔
b. «repeated» within the range of the optimum pH
OR
between pH 6/7 and 8 ✔
c. the pH that gives the highest enzyme activity is optimum ✔
Candidates found this question to be challenging. Students were asked to “explain how a more exact value for the optimum pH could be determined.” Students who completed practical 3 and were also taught the second skill listed in the subject guide in topic 2.5 (Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes) should have been able to achieve the marks. Common incorrect answers suggested using better graphs or different calculation methods. Students should be instructed to understand the difference between experimental methods and data-processing tools.
