In biochemistry, the term metabolism refers to which of the following?

• A. The passive diffusion of molecules across biological membranes without energy input
• B. Only the synthesis of complex molecules from simpler precursors (anabolism)
• C. Only the breakdown of complex molecules into simpler molecules to release energy (catabolism)
• D. The sum of all chemical reactions in a cell or organism, including both catabolic and anabolic pathways

Answer: (D)