Explain how enzymes, such as hexokinase, are able to catalyse reactions.

State and explain the effect of increasing the temperature from 20 °C to 60 °C on an enzyme-catalysed reaction.

enzymes have an active site (where the substrate can bind) / explanation of lock and key or induced fit model;

lowers activation energy (by providing an alternative pathway);

increasing temperature initially increases rate of reaction;

because more molecules possess energies equal or greater than the activation energy;

at a temperature around 37 °C, the highest rate is reached;

at a temperature around 40 °C the enzyme is denatured / shape of the active site changes/tertiary structure of the enzyme changes;

so rate decreases/reaction stops;

In the explanation of how enzymes are able to catalyse reactions, many referred to active sites but fewer made reference to the lowering of activation energy.

Though candidates seemed to understand enzyme activity at different temperatures, they often omitted details on the exact temperature ranges. Some were nicely able to illustrate their answer with a properly labelled graph.