Correct Response: B. During many metabolic reactions, enzymes facilitate the transfer of a phosphate group from adenosine triphosphate, or ATP, to one of the reactant molecules. Bonds with phosphate groups tend to contain a lot of chemical potential energy, which has now been transferred to the reactant in the metabolic process and can be used to drive the metabolic reaction forward. Although hydrolysis of a phosphate group will release heat (A), this heat is dissipated and its energy is unavailable to drive a metabolic reaction forward. Lowering the activation energy is often required for phosphorylation (C), but this process is generally facilitated by enzymes. Absorption of light by chlorophyll does help provide the energy needed to generate ATP during photosynthesis. However, absorption of light by pigments (D) is not a general mechanism used by the cell to drive metabolic reactions.
