3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
The enzyme sucrase catalyses the breakdown of the glycosidic bond in sucrose. A student investigated the effect of increasing the concentration of sucrose on the rate of activity of sucrase. Ten test-tubes were set up with each containing 5 cm3 of different concentrations of a sucrose solution. The test-tubes were placed in a water bath at 40 °C for ten minutes. A flask containing a sucrase solution was also put into the water bath. After ten minutes, 1 cm3 of the sucrase solution was added to each test-tube. The reaction mixtures were kept at 40 °C for a further ten minutes. After ten minutes, the temperature of the water bath was raised to boiling point. Benedict’s solution was added to each test-tube. The time taken for a colour change was recorded and used to calculate rates of enzyme activity. The results are shown in . concentration of sucrose / g dm–3 rate of enzyme activity / arbitrary units Name the type of reaction catalysed by sucrase. Explain why the temperature of the water was raised to boiling point. Describe and explain the results shown in .
9700_s11_qp_21
THEORY
2011
Paper 2, Variant 1
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Catalase is an enzyme that catalyses the conversion of hydrogen peroxide into water and oxygen. Two students investigated the effect of enzyme concentration on the rate of reaction of the enzyme catalase. The students predicted their results would show the same trend. The graphs show the rates obtained by each student. initial rate of reaction / cm3 oxygen min–1 enzyme concentration student 1 initial rate of reaction / cm3 oxygen min–1 enzyme concentration student 2 Which statement explains the different trend shown...
9700_s12_qp_11
MCQ
2012
Paper 1, Variant 1
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Catalase is an enzyme that catalyses the conversion of hydrogen peroxide into water and oxygen. Two students investigated the effect of enzyme concentration on the rate of reaction of the enzyme catalase. The students predicted their results would show the same trend. The graphs show the rates obtained by each student. initial rate of reaction / cm3 oxygen min–1 enzyme concentration student 1 initial rate of reaction / cm3 oxygen min–1 enzyme concentration student 2 Which statement explains the different trend shown...
9700_s12_qp_13
MCQ
2012
Paper 1, Variant 3
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The enzyme, catechol oxidase, causes a brown colour to develop when slices of many fruits, such as apples, are exposed to air. The enzyme catalyses the following reaction: catechol oxidase catechol + oxygen quinone + water Quinone is then immediately further oxidized in air to a brown-coloured substance. Catechol and quinone are colourless. A student investigated the rate of this reaction under different conditions. State how the student could follow the progress of this reaction. In the first investigation, the student measured the initial rate of the reaction in varying concentrations of catechol. The results are shown in . concentration of catechol / mM initial rate of reaction / arbitrary units Explain the results shown in . In a second investigation, the student repeated the experiment, but this time added a competitive inhibitor, para-hydroxybenzoic acid (PHBA), to each reaction mixture. Sketch on the results that would be obtained for this second investigation. Explain the effect that PHBA will have on the action of phenoloxidase. Lemon juice contains citric acid. Adding even a small amount of diluted lemon juice to apple slices slows the appearance of the brown colour. Suggest an explanation for this observation.
9700_s13_qp_23
THEORY
2013
Paper 2, Variant 3
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Lipase is an enzyme with many commercial uses. Some species of bacteria are of great interest as they produce large quantities of lipase. Complete to show the hydrolysis of triglyceride by lipase. lipase triglyceride + Researchers carried out investigations into lipase extracted from a bacterium found in hot springs. To measure the activity of the bacterial lipase during their investigations, the researchers used a method based on the biological test for triglycerides. Outline a biological test that could be carried out to show the presence of triglyceride in a liquid mixture and describe the positive result for this test. The researchers investigated the effect of pH values between pH 2.0 and pH 10.5 on the activity of bacterial lipase in hydrolysing triglyceride at a temperature of 37 °C. The results are shown in . 2.0 1.0 4.0 3.0 6.0 pH percentage activity 5.0 8.0 7.0 10.0 9.0 12.0 11.0 With reference to , describe the effect of pH on the activity of bacterial lipase. A separate investigation into the effect of pH on the same bacterial lipase compared the enzyme free in solution with the enzyme immobilised by physical attachment to a stable polymer. At a temperature of 37 °C, the optimum pH of the enzyme free in solution was the same as that shown in . The optimum pH of the immobilised enzyme was measured as pH 4. Suggest one reason to explain why the enzyme free in solution has a different optimum pH compared to the immobilised enzyme. Suggest one advantage of immobilising the extracted lipase for commercial use.
9700_s17_qp_22
THEORY
2017
Paper 2, Variant 2
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Questions Discovered
276