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CAIE IGCSE Biology 5 Enzymes

Practise defining enzymes, interpreting active-site models and explaining how temperature, pH and specificity affect activity.

Syllabus
2026–2028
Course
Biology 0610

Covered syllabus points

5.1 Enzymes

5. Enzymes question 1

[Maximum number: 9]

Enzymes are biological catalysts.

Question (a)

(a)

Describe what is meant by the term catalyst.

[ 2 ]

Question (b)

(b)

A student investigated the effect of temperature on enzyme activity.

A starch suspension was kept at 0∘C0^{\circ} \mathrm{C}.
Amylase solution was added to the starch suspension.
Samples of the starch and amylase mixture were tested with iodine solution at 1 -minute intervals for 15 minutes.

The student recorded the time at which the starch and amylase mixture stopped turning a blue-black colour.

The student repeated this investigation at different temperatures.
Table 3.1 shows the results.

Table 3.1

Table 3.1

[ 6 ]

Question (i)

(i)

Explain the results between 0∘C0^{\circ}\mathrm{C} and 40∘C40^{\circ}\mathrm{C} in Table 3.1.

[ 6 ]

Question (c)

(c)

State one factor, other than temperature, that affects enzyme action.

[ 1 ]

5. Enzymes question 2

[Maximum number: 1]

In addition to sucrose, amino acids are also transported in plants.

State the name of the group of molecules that are made of proteins and act as catalysts.

5. Enzymes question 3

[Maximum number: 1]

Which statement is correct?

A

The active site of an enzyme has the same shape as the substrate.

B

The active site is not affected by changes in temperature.

C

The shape of the active site of an enzyme is complementary to its substrate.

D

The substrate and product combine at the active site.

5. Enzymes question 4

[Maximum number: 1]

Fig. 1.1 shows several villi from the ileum, which is part of the small intestine.

Many fungi are decomposers that feed on dead plants. The fungi secrete enzymes to digest large molecules.

Students made an extract from a species of fungus. The extract contained digestive enzymes.
The students carried out an investigation to find out if amylase and pectinase were present in the fungal extract.

They made agar plates by filling Petri dishes with agar jelly containing either starch or pectin. They cut four holes of the same size in the agar jelly in each Petri dish.

The holes in each Petri dish contained the same volume of:

A - 1\% amylase solution

B - 1\% pectinase solution

C - distilled water

D - fungal extract. The Petri dishes were kept at 27∘C27^{\circ} \mathrm{C} for four days. After this time a dye was poured into each dish to stain the areas where starch and pectin remained. Fig. 1.3 shows drawings of the stained agar in the Petri dishes. The clear zones indicate the areas where no starch or pectin remained.

Fig. 1.3

Fig. 1.3

The investigation was repeated but at 5∘C5^{\circ} \mathrm{C} instead of at 27∘C27^{\circ} \mathrm{C}.

Predict the effect of the lower temperature on the results.

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