1. The problem asks: What is the function of an enzyme in a biochemical reaction? 2. Enzymes are biological catalysts that speed up chemical reactions without being consumed. 3. They do this by lowering the activation energy required for the reaction to proceed. 4. Enzymes do not increase the amount of substrate, raise the temperature, or change the type of product formed. 5. Therefore, the correct answer is: speed up the rate of the reaction. Final answer: speed up the rate of the reaction.