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Date May 2019 Marks available 1 Reference code 19M.3.HL.TZ1.1
Level Higher level Paper Paper 3 Time zone Time zone 1
Command term Suggest Question number 1 Adapted from N/A

Question

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.]

State the effect immobilization of lipase has on its optimum temperature.

[1]
a.

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]
b.

Based on these experimental results, suggest one advantage of immobilizing lipase.

[1]
c.

Markscheme

it is increased ✔

a.

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 ✔

b.

a. it increases the range of temperature/pH that give high activity ✔ 

b. allows for commercial use in detergents ✔

c.

Examiners report

This question was handled well by most students, who were able to see that immobilization increased the optimum temperature. Some candidates did miss the mark by only stating numerical values or commenting on the range of temperatures used, and therefore not the optimum temperature.

a.

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.

b.

Most candidates saw that the enzymes could work at a higher temperature and a broader range of temperature and pH values and were therefore able to achieve 1 mark. Few students could connect this to the industrial uses for enzymes. This was one of many instances in the paper where students’ inability to use precise language affected their scores. Specifically, students should be reminded that terms like “affect” and “change” do not communicate differences in data as well as words like “increase” and “decrease.”

c.

Syllabus sections

Core » Topic 2: Molecular biology » 2.5 Enzymes
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