A student investigates how temperature affects the activity of catalase, an enzyme extracted from mushroom tissue that catalyses the breakdown of hydrogen peroxide into water and oxygen. At each temperature, the student mixes the same volume and concentration of mushroom extract…

Answer: ((a)) The volume of oxygen collected increases as temperature rises from 10°C to 40°C (from 4 cm3 up to a peak of 23 cm3), then decreases sharply as temperature rises further from 40°C to 60°C (falling to just 1 cm3). The greatest volume of oxygen, and so the fastest rate of reaction,… ((b)) As temperature increases, both enzyme and substrate molecules gain more kinetic energy and move around faster. This means they collide with each other more frequently, and a greater proportion of these collisions have enough energy to succeed. As a result, more enzyme-substrate… ((c)) Above the optimum temperature, the enzyme molecules vibrate more and more vigorously. This extra vibration breaks the hydrogen bonds and ionic bonds that hold the enzyme's tertiary structure in its precise three-dimensional shape. As these bonds break, the shape of the active si…. Part (a): Describing the pattern Reading across the table, the volume of oxygen collected rises steadily as the temperature increases from 10°C (4 cm3) to 40°C (23 cm3). Above 40°C, the trend reverses: the volume collected falls sharply, d…

AS & A Level Biology 9700: Explaining the Effect of Temperature on Enzyme Activity

Temperature / °C	10	20	30	40	50	60
Volume of oxygen collected in 2 minutes / cm3	4	9	15	23	6	1

Temperature / °C

Volume of oxygen collected in 2 minutes / cm3

Part (a): Describing the pattern

Reading across the table, the volume of oxygen collected rises steadily as the temperature increases from 10°C (4 cm3) to 40°C (23 cm3). Above 40°C, the trend reverses: the volume collected falls sharply, dropping to only 6 cm3 at 50°C and just 1 cm3 at 60°C.

So the overall pattern is a rise to a peak at 40°C, followed by a sharp fall. 40°C is the temperature at which the reaction proceeds fastest for this enzyme, its optimum temperature.

Part (b): Why the rate increases between 10°C and 40°C

Temperature is a measure of the average kinetic energy of particles. As the temperature rises from 10°C to 40°C:

Both the catalase molecules and the hydrogen peroxide molecules gain kinetic energy and move faster.
Faster-moving molecules collide with each other more frequently.
A greater proportion of these collisions also have enough energy to overcome the activation energy of the reaction (which the enzyme has already lowered by forming an enzyme-substrate complex).

Together, more frequent and more successful collisions mean more enzyme-substrate complexes form every second, so hydrogen peroxide is converted to water and oxygen at a faster rate, producing a greater volume of oxygen in the same fixed two-minute collection time.

Part (c): Why the rate falls sharply between 40°C and 60°C

Beyond the optimum temperature, the extra kinetic energy no longer just speeds up useful collisions. It also makes the atoms within each enzyme molecule vibrate more vigorously. This vibration is enough to break some of the hydrogen bonds and ionic bonds that hold catalase’s tertiary (three-dimensional) structure in its precise folded shape.

Because the active site’s shape depends on this overall three-dimensional structure, breaking these bonds distorts the active site so that it is no longer complementary to the shape of the hydrogen peroxide molecule. The enzyme is denatured. A denatured enzyme can no longer bind its substrate effectively (or at all), so fewer enzyme-substrate complexes form.

As temperature rises further from 40°C to 60°C, an increasing proportion of the catalase molecules become denatured, so the volume of oxygen produced falls sharply. Most enzyme molecules are inactive by 60°C, leaving almost no reaction taking place.

Final answers

(a) The volume of oxygen rises to a peak of 23 cm3 at 40°C (the optimum temperature), then falls sharply to 1 cm3 by 60°C.
(b) Higher temperature gives molecules more kinetic energy, causing more frequent, more successful collisions between enzyme and substrate, forming more enzyme-substrate complexes per unit time.
(c) Above the optimum, vibration breaks the hydrogen and ionic bonds holding the enzyme’s tertiary structure, changing the active site’s shape so it is no longer complementary to the substrate. The enzyme is denatured and can no longer catalyse the reaction efficiently.