Answer: A. The enzyme influences the speed of change from substrate to product.
By lowering the activation energy of the reaction, enzymes help to speed up rate of reaction without affecting the chemical composition of that reaction. Without enzymes in the body, there will be no reaction in the body as most reactions happening in the body are entirely catalytic. While the enzyme catalyzes the reaction, the substrate is the molecule which an enzyme acts on. Generally, the substrate is changed into a product or products and then released from the active site of an enzyme. So in summary, the substrate binds with the enzyme at a point called the active site, undergoes a series of chemical reactions, and then is released from the same active site as a whole new product.