Enzymes and chemical digestionIB MYP Sciences: Flashcards

Exam questions on Enzymes and chemical digestion

1. A manufacturer in Gothenburg sells a biological washing powder that contains the enzymes protease and lipase. The powder removes food stains from clothes in water at 40 °C, but it works poorly in boiling water.
   Explain why the protease in the powder does not break down grease stains.2 marks
2. Pepsin is a protease made in the stomach, where hydrochloric acid gives the gastric juice a pH of about 2. Amylase in saliva works best at about pH 7. Swallowed food, mixed with saliva, passes from the mouth into the stomach and then into the small intestine, where bile and pancreatic juice raise the pH to about 8.
   Explain why pepsin stops working when it passes into the small intestine.2 marks
3. A student in Johannesburg mixes amylase solution with starch solution at five different temperatures. At each temperature she tests a drop of the mixture with iodine solution every 15 seconds, until the drop no longer turns blue-black. At 10 °C this took 300 seconds, at 20 °C it took 150 seconds, at 30 °C 80 seconds and at 40 °C 45 seconds. At 60 °C the drop still turned blue-black after 600 seconds.
   Describe the results of the investigation.3 marks