1. 1
   A manufacturer of biological washing powder adds protein-digesting enzymes to help remove stubborn stains such as blood and grass. The instructions recommend washing at 40°C, warning that washing at much higher temperatures makes the powder far less effective at removing stains.

   (a)

   What term is used to describe the protein-digesting enzymes added to the biological washing powder?

   [1 mark]

   • ABiological catalysts
   • BHormones
   • CAntibodies
   • DStructural proteins

   (b)

   Which model describes how the enzyme's active site is a specific shape that fits only its target substrate (such as the protein stain molecules)?

   [1 mark]

   • AThe induced fit model
   • BThe lock and key model
   • CThe double helix model
   • DThe particle model

   (c)

   Explain why washing at a much higher temperature than 40°C makes the biological washing powder far less effective at removing stains.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student carries out an experiment using the enzyme pepsin, which digests protein in the stomach, testing its activity at a range of pH values from pH 1 to pH 9, keeping temperature and substrate concentration constant. The results show the enzyme works fastest at a low pH, similar to the acidic conditions in the stomach, but activity drops sharply above pH 4.

   (a)

   Based on the results, which pH range is closest to the optimum pH for pepsin?

   [1 mark]

   • ApH 8–9
   • BpH 6–7
   • CpH 1–2
   • DpH 10–11

   (b)

   What is the main reason pepsin's activity drops sharply above pH 4?

   [1 mark]

   • AThe substrate runs out
   • BThe enzyme concentration increases
   • CThe reaction speeds up too quickly
   • DThe enzyme's active site changes shape (denatures)

   (c)

   Explain what happens to pepsin's active site at pH values far from its optimum, and the effect this has on its function.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A biotechnology company tests how quickly an amylase enzyme breaks down starch, using different concentrations of substrate and different concentrations of enzyme, while keeping the temperature and pH constant throughout.

   (a)

   Explain the effect of increasing substrate concentration on the rate at which the amylase enzyme breaks down starch, while enzyme concentration, temperature and pH are kept constant.

   [3 marks]

   (b)

   Explain the effect of increasing enzyme concentration on the rate at which starch is broken down, while substrate concentration, temperature and pH are kept constant.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Scientists investigating enzyme activity have long used simple laboratory experiments, such as mixing amylase with starch solution and testing for the disappearance of starch using iodine at set time intervals, or measuring the rate of oxygen bubble production when catalase reacts with hydrogen peroxide, to explore how enzymes work and what affects their activity.

   (a)

   Describe enzymes as biological catalysts, and describe the lock and key model and the induced fit model of enzyme action.

   [6 marks]

   (b)

   Describe the effect of temperature and pH on enzyme activity, and describe how you could investigate one of these factors using amylase and starch, or catalase and hydrogen peroxide.

   [6 marks]

   Total for question 4: 12 marks

End of questions