CAIE IGCSE Biology 5.1.5 Temperature, pH & Enzyme Activity

Practise investigating enzyme activity and identifying optimum temperature or pH and evidence of denaturation from data.

Exam points

identify an optimum as the condition with greatest rate, shortest time or largest measured product
describe a temperature or pH trend using values and distinguish a peak from the point activity reaches zero
identify temperature, pH, enzyme concentration and substrate concentration as conditions to control in an enzyme investigation

[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 $27^{\circ} \mathrm{C}$ 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

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

Predict the effect of the lower temperature on the results.

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5.1.5—Temperature, pH and enzyme activity question 1