Enzymes, such as the one shown in the picture, work by fitting onto the substrate molecule like a lock-and-key action. Which statement is true, with regard to the enzyme and the substrate? A) The enzyme weakens chemical bonds in the substrate and catalyzes a change into the product. The enzyme itself remains unchanged. B) The enzyme weakens chemical bonds in the substrate and catalyzes a change into the product. The enzyme is also consumed in the reaction. C) The substrate reacts with the enzyme in the active site to produce a product. The enzyme, though changed, does not become a part of the product. D) The substrate reacts with the enzyme in the active site to produce a product. Both the enzyme and the substrate combine and change into a product.

Enzymes are biological catalysts that speed up the rate of biochemical reactions but they are not used up in the process. Enzymes speed up chemical reactions by lowering the activation energy of the reaction. All chemical reactions have activation energy, this is the smallest amount of energy that the reacting species must possess before they can under a chemical reaction. When an enzyme lower this energy the reaction occurs faster but the enzyme remains unchanged.