Final answer:
An enzyme is a reusable biological catalyst that speeds up chemical reactions by lowering the activation energy required for the reaction.
Step-by-step explanation:
The correct statement that accurately describes an enzyme is: d) An enzyme is reusable and increases the rate of a chemical reaction by lowering the activation energy. Enzymes are remarkable biological catalysts that are composed of amino acids and are not consumed or altered in the reaction. They work by providing an alternative pathway with a lower activation energy for the reaction to proceed, which significantly speeds up the rate of the reaction. Furthermore, enzymes are highly specific, meaning each kind of enzyme only works with certain substrates, fitting into its active site almost like a key fits into a lock, a concept often described by the lock-and-key model or the induced-fit model. This specificity ensures that enzymes facilitate the correct chemical reactions within the cell.