CAIE IGCSE Biology 5.1 Enzyme Action & Activity

Practise applying catalyst definitions, enzyme specificity and active-site changes to reaction diagrams, graphs and data.

Exam points

label enzyme, active site, substrate, enzyme-substrate complex and products in reaction models
explain specificity through a complementary active site and why one enzyme acts on particular substrates
interpret temperature or pH data using collisions below optimum and active-site denaturation beyond it

Covered syllabus points

5.1.1—Catalyst as a substance that increases 5.1.2—Enzymes as proteins that are involved 5.1.3—Why enzymes are important in all 5.1.4—Enzyme action with reference 5.1.5—Temperature, pH and enzyme activity 5.1.6—Enzyme action with reference 5.1.7—Specificity of enzymes in terms 5.1.8—Effect of changes in temperature on 5.1.9—Effect of changes in pH on enzyme

[Maximum number: 9]

Enzymes are biological catalysts.

(a)

Describe what is meant by the term catalyst.

[ 2 ]

(b)

A student investigated the effect of temperature on enzyme activity.

A starch suspension was kept at $0^{\circ} \mathrm{C}$ .
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

[ 6 ]

(i)

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

[ 6 ]

(c)

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

[ 1 ]

[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.

[Maximum number: 1]

Which statement is correct?

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

The active site is not affected by changes in temperature.

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

The substrate and product combine at the active site.

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Covered syllabus points

5.1 Enzymes question 1

Question (a)

Question (b)

Question (i)

Question (c)

5.1 Enzymes question 2

5.1 Enzymes question 3