2.8 understand the role of enzymes as biological catalysts in metabolic reactions

The most important thing to know about enzymes is that they are chemically unchanged throughout the reaction. Enzymes speed up a reaction by lowering the activation energy of a reaction.

Making a reaction faster and being unchanged are the basic characteristics of a catalyst, therefore, as enzymes speed up reactions and are chemically unchanged throughout the reaction, they are known as biological catalysts.

(for more information on enzymes that is not directly in the spec but may be useful for your understanding : http://www.abpischools.org.uk/page/modules/enzymes/enzymes5.cfm?coSiteNavigation_allTopic=1 )