Final answer:
If an enzyme is not functioning in a chemical reaction in a living organism that needs it, the reaction will proceed at a slower rate.
Step-by-step explanation:
When an enzyme is not functioning in a chemical reaction in a living organism that needs it, the reaction will typically proceed at a slower rate (option a). Enzymes are biological catalysts that lower the activation energy required for a reaction to occur. Without the enzyme, more energy is needed for the reaction to begin, resulting in a slower rate of reaction.