Metabolism refers to series of reactions wherein product of one reaction becomes reactant for the next one. It includes catabolism (degradative pathways) and anabolism (synthetic pathways). Catabolic reactions are the reactions in which complex molecules are broken down into smaller simpler molecules. The catabolic reactions are exergonic reactions( energy releasing reactions). While photosynthesis is an anabolic reaction which requires energy for the formation of complex molecules. Hence option B is the correct answer.