EnzymesIB MYP Biology: Subtopic test

1. 1
   A patient in Dubai whose pancreas is damaged cannot make enough of its digestive enzymes. Her doctor prescribes capsules containing the enzyme lipase to be taken with every meal.

   (a)

   What is an enzyme?

   [1 mark]

   • AA chemical that is used up as it speeds up a reaction
   • BA living cell that digests food
   • CA biological catalyst that speeds up a reaction without being used up
   • DA hormone that carries messages in the blood

   (b)

   Which products are made when lipase digests fat?

   [1 mark]

   • AFatty acids and glycerol
   • BAmino acids
   • CGlucose
   • DMaltose

   (c)

   Explain why lipase can digest fat but cannot digest protein.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Seoul investigates how temperature affects the activity of the enzyme amylase. She mixes 5 cm³ of starch solution with 2 cm³ of amylase solution in a test tube kept in a water bath. Every 30 seconds she puts a drop of the mixture into iodine solution on a spotting tile and records the time at which the iodine stops turning blue-black. She repeats this at 20 °C, 30 °C, 40 °C, 50 °C and 60 °C. The times taken were 240 s, 120 s, 60 s and 90 s for the first four temperatures. At 60 °C the iodine was still turning blue-black after 600 s.

   (a)

   What is the dependent variable in this investigation?

   [1 mark]

   • AThe temperature of the water bath
   • BThe time taken for the iodine to stop turning blue-black
   • CThe volume of starch solution
   • DThe concentration of amylase

   (b)

   Which statement best explains the result at 60 °C?

   [1 mark]

   • AThe amylase was used up in the reaction
   • BAll the starch had already been changed to glucose
   • CThe water bath was too cold for the reaction
   • DThe active site of amylase changed shape, so starch no longer fitted

   (c)

   Describe the trend in the results between 20 °C and 40 °C.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The enzyme pepsin, a protease made in the human stomach, works best at about pH 2. Another protease made by the pancreas works in the small intestine, where the pH is about 8.

   (a)

   Explain why pepsin would not digest protein well if it were carried into the small intestine.

   [3 marks]

   (b)

   Outline a safe method to investigate how pH affects the rate at which a protease digests protein, such as small cubes of cooked egg white.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company in Johannesburg sells a biological washing powder that contains the enzymes protease, lipase and amylase. The powder cleans clothes well at 30 °C. Older non-biological powders need a 60 °C wash to remove the same stains. The label on the biological powder warns that it should not be used in boiling water.

   (a)

   Explain how the enzymes in the biological washing powder remove food stains from clothes and why they stop working in boiling water.

   [6 marks]

   (b)

   Discuss and evaluate the use of biological washing powder at 30 °C instead of non-biological powder at 60 °C.

   [6 marks]

   Total for question 4: 12 marks

End of questions