Enzymes and chemical digestionIB MYP Sciences: Subtopic test

1. 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.

   (a)

   Which of these stains would lipase in the powder help to remove?

   [1 mark]

   • AEgg white
   • BCooked rice
   • CButter
   • DSugar syrup

   (b)

   Which products are made when protease breaks down protein?

   [1 mark]

   • AAmino acids
   • BFatty acids and glycerol
   • CMaltose
   • DStarch

   (c)

   Explain why the protease in the powder does not break down grease stains.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   What would happen to salivary amylase when it reaches the stomach?

   [1 mark]

   • AIt would work faster because acid is a catalyst
   • BIt would be unaffected because enzymes do not depend on pH
   • CIt would start to digest protein
   • DIt would be denatured because the pH is too low

   (b)

   Which organs make amylase?

   [1 mark]

   • AStomach and liver
   • BSalivary glands and pancreas
   • CGall bladder and liver
   • DOesophagus and large intestine

   (c)

   Explain why pepsin stops working when it passes into the small intestine.

   [2 marks]

   Total for question 2: 4 marks

3. 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.

   (a)

   Describe the results of the investigation.

   [3 marks]

   (b)

   Explain the results at 40 °C and at 60 °C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student in Lagos suggests that amylase works fastest at pH 7, because saliva is neutral. She has amylase solution, starch solution, iodine solution, a spotting tile, a water bath, a stopwatch and buffer solutions of pH 3, 5, 7 and 9. Her teacher also mentions that people whose pancreas does not release enough digestive enzymes can take tablets containing amylase, protease and lipase with every meal.

   (a)

   Design an investigation to test the student's suggestion that amylase works fastest at pH 7.

   [6 marks]

   (b)

   Discuss and evaluate the use of enzyme tablets by people whose pancreas does not release enough digestive enzymes.

   [6 marks]

   Total for question 4: 12 marks

End of questions