Factors affecting enzyme activityAQA A-Level Biology: Mind map

Exam questions on Factors affecting enzyme activity

1. A student investigates the effect of temperature on the rate of the reaction catalysed by catalase in potato tissue. She adds 5 g of potato tissue to 20 cm³ of hydrogen peroxide solution at each temperature and collects the oxygen produced for 60 seconds. The volumes of oxygen collected at 20 °C, 30 °C, 40 °C, 50 °C and 60 °C were 4.0 cm³, 9.0 cm³, 15.0 cm³, 3.5 cm³ and 0 cm³ respectively.
   Explain why less oxygen was collected at 50 °C than at 40 °C.2 marks
2. Pepsin is a protease secreted into the stomach, where the hydrogen ion concentration of the gastric juice is 6.3 × 10⁻³ mol dm⁻³. Its optimum pH is about 2. Trypsin is a protease secreted into the small intestine, where the pH is about 8, and its optimum pH is about 8.
   Explain why pepsin is inactive when it passes into the small intestine.2 marks
3. Succinate dehydrogenase catalyses the oxidation of succinate in respiration. Malonate has a molecular shape very similar to succinate and reduces the rate of this reaction. A student also tests inhibitor Q, which binds to a site on the enzyme away from the active site. With malonate present, increasing the succinate concentration to a very high value raises the rate almost to the rate with no inhibitor. With inhibitor Q present, the rate stays well below the rate with no inhibitor, even at very high succinate concentration.
   Explain how malonate reduces the rate of the reaction catalysed by succinate dehydrogenase.3 marks