which statement best describes how enzymes affect the speed of a metabolic reaction? a. enzymes increase the concentration of reactants, which increase the speed of the reaction. b. enzymes decrease the energy needed to start a reaction, which increases the speed of the reaction. c. enzymes replace the reactants in a chemical reaction, which decreases the speed of the reaction. d. enzymes prevent products from being converted back into reactants, which decreases the speed of the reaction.
