EnzymesCambridge IGCSE Biology: Topic test

20 questions, 54 marks

Cambridge IGCSE Biology

Enzymes topic test

Total 54 marks

Name

Class

Date

1
A detergent company adds a protease enzyme to a biological washing powder because it breaks down protein-based stains, such as blood and egg, into smaller, soluble molecules that rinse away easily. The instructions recommend washing at 40 degrees Celsius rather than at 90 degrees Celsius.
(a)
What term describes a substance, such as the protease in the washing powder, that increases the rate of a chemical reaction and is not changed by the reaction itself?
[1 mark]
ACatalyst
BSubstrate
CProduct
DSolvent
(b)
Protease molecules are all made of the same class of biological molecule. Which class is this?
[1 mark]
ACarbohydrate
BProtein
CLipid
DNucleic acid
(c)
Explain why the washing instructions recommend 40 degrees Celsius rather than 90 degrees Celsius for a wash containing this enzyme.
[2 marks]
Total for question 1: 4 marks
2
A brewery germinates barley seeds to produce malt. As the seeds germinate they produce an amylase enzyme that breaks down the starch stored in the seed into smaller sugar molecules that yeast can later use.
(a)
Amylase breaks down starch but has no effect on the protein or fat also present in the barley seed. What property of enzymes does this illustrate?
[1 mark]
ADenaturation
BOptimum temperature
CSpecificity
DActivation energy
(b)
Which structure of the amylase molecule is responsible for it only acting on starch?
[1 mark]
AIts active site
BIts cell wall
CIts nucleus
DIts cytoplasm
(c)
Explain, in terms of the active site, why the amylase produced by the germinating barley seed breaks down starch but cannot break down protein molecules.
[2 marks]
Total for question 2: 4 marks
3
A food company uses the enzyme invertase, produced by yeast, to break down sucrose into glucose and fructose for use in soft-centred sweets. Technicians measure the rate of sucrose breakdown by invertase at a range of pH values, keeping temperature and enzyme concentration constant. The highest rate was recorded at pH 4.5, with lower rates recorded at pH values above and below this.
(a)
Explain, in terms of shape and fit, why the rate of sucrose breakdown by invertase was highest at pH 4.5 but lower at pH values above and below this.
[3 marks]
(b)
The technicians also tested invertase at pH 2.5, a value far from its optimum, and found that afterwards its activity did not recover even when the pH was returned to 4.5. Explain this observation, and describe what would happen to the rate of sucrose breakdown if the enzyme concentration were doubled at the optimum pH, with substrate in excess.
[4 marks]
Total for question 3: 7 marks
4
An enzyme development team is comparing two protease enzymes for use in a stain-removal product: enzyme X, extracted from a bacterium that lives in hot springs at around 70 degrees Celsius, and enzyme Y, extracted from a bacterium that lives in ordinary soil at around 25 degrees Celsius. Both enzymes break down the same protein stains but work best under different conditions.
(a)
Explain, in terms of kinetic energy, shape and fit, and frequency of effective collisions, why increasing the temperature of a reaction mixture containing enzyme Y from 10 degrees Celsius up to its optimum increases the rate of protein breakdown, and why a further increase in temperature beyond the optimum then causes the rate to fall sharply.
[6 marks]
(b)
The team finds that enzyme X still works well at 70 degrees Celsius, a temperature at which enzyme Y is completely denatured. Explain why the two enzymes have such different optimum temperatures despite both being proteases that break down the same protein stain, and explain why this difference matters when choosing which enzyme to use in a washing powder intended for washes at 60 degrees Celsius.
[6 marks]
Total for question 4: 12 marks
5
A dairy company passes milk over lactase enzyme immobilised on small beads to break down the milk sugar lactose into glucose and galactose, producing lactose-free milk. The process is carried out at 37 degrees Celsius, the temperature at which the company's lactase works fastest.
(a)
What name is given to the temperature at which an enzyme such as this lactase works fastest?
[1 mark]
AMelting point
BOptimum temperature
CBoiling point
DActivation temperature
(b)
If the milk were instead heated to 95 degrees Celsius before adding the lactase, what would happen to the rate of lactose breakdown?
[1 mark]
AIt would increase further above the rate at 37 degrees Celsius
BIt would stay exactly the same as at 37 degrees Celsius
CIt would fall to almost zero because the lactose would be denatured
DIt would fall to almost zero because the lactase would be denatured
(c)
Explain why the dairy company carries out the process at 37 degrees Celsius rather than at 95 degrees Celsius.
[2 marks]
Total for question 5: 4 marks
6
A food scientist extracts the enzyme papain from papaya fruit and tests it as a meat tenderiser. When mixed separately with samples of protein, starch and fat, papain only breaks down the protein sample.
(a)
Papain breaking down protein but not starch or fat is an example of which property of enzymes?
[1 mark]
AOptimum pH
BDenaturation
CSpecificity
DCatalysis rate
(b)
Which term describes the protein molecules that papain binds to and breaks down?
[1 mark]
AProduct
BCatalyst
CCofactor
DSubstrate
(c)
Explain, in terms of the active site, why papain breaks down protein but has no effect on starch or fat.
[2 marks]
Total for question 6: 4 marks
7
A cheesemaker adds the enzyme chymosin (rennin) to warm milk to clot the milk protein casein, forming curds used to make cheese. Trials at three temperatures, keeping chymosin concentration and milk volume constant, recorded the time taken for clotting to begin: 210 seconds at 20 degrees Celsius, 70 seconds at 35 degrees Celsius (the enzyme's optimum), and clotting did not occur within 30 minutes at 85 degrees Celsius.
(a)
Explain why clotting began fastest at 35 degrees Celsius but took much longer at 20 degrees Celsius.
[3 marks]
(b)
Explain why clotting did not occur within 30 minutes at 85 degrees Celsius, and describe what result you would predict if the trial at 85 degrees Celsius were repeated with double the concentration of chymosin.
[4 marks]
Total for question 7: 7 marks
8
A biochemist compares two protease enzymes: enzyme P, used in a dishwasher detergent that operates at pH 10, and pepsin, a human digestive protease that works in the stomach at pH 2. Both enzymes break down protein molecules, but each only works efficiently within its own narrow pH range.
(a)
Explain, in terms of shape and fit and denaturation, why enzyme P works efficiently at pH 10 but would stop working if the dishwasher water became acidic at pH 4, and why pepsin shows the opposite pattern, working at pH 2 but not at pH 10.
[6 marks]
(b)
Explain why it would be pointless for the dishwasher manufacturer to add pepsin to the detergent instead of enzyme P, and explain one advantage to a living organism of enzymes such as pepsin only working efficiently within a narrow pH range rather than across all pH values.
[6 marks]
Total for question 8: 12 marks

End of questions