O-LevelBiologyEnzymes5090/22 · May/June 2015 · Q19 Marks

Fig. 1.1 shows the effect of temperature on the rate at which yeast cells in a nutrient solution produce bubbles of a gas. [Figure 1.1]

(a)Name each of the following: • the gas released • the metabolic process that releases it • the essential chemical constituents of the nutrient solution. and[3]
(b)Use Fig. 1.1 to find the optimum temperature for the metabolic process.[1]
(c)Explain the shape of the curve after 60 °C.[3]
(d)Explain what would happen to the rate at which bubbles of the gas are produced by the yeast if the temperature of the solution is then gradually reduced from 65 °C to 45 °C.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[3] (a) carbon dioxide/CO2;
[3] (a) respiration/fermentation ;
[3] (a) any two for one mark: sugar OR carbohydrates OR named/water/protein OR amino acids/oxygen/lipids OR fats/mineral ions OR named ; A two named mineral ions for 1 mark
[1] (b) any temperature in range 56 – 58 °C ;
[3] (c) 1. rate decreases + zero/stops; A number of bubbles per (two) minutes(s)
[3] (c) 2. enzymes; R denaturing of yeast/killing of enzymes
[3] (c) 3. denatured ;
[3] (c) 4. references to active site/lock and key hypothesis ;
[3] (c) 5. yeast dies/destroyed/killed ;
[2] (d) 1. rate remains at zero/stays the same/no change/no effect ; A no gas production/no bubbles
[2] (d) 2. denaturing is permanent/enzymes still denatured ; A active site still changed
[2] (d) 3. death of yeast;

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