The chemical process that breaks substances down to produce energy is called ____.

The correct answer is metabolism, which refers specifically to the set of life-sustaining chemical reactions in organisms. Metabolism encompasses two fundamental processes: catabolism and anabolism. Catabolism is the breakdown of larger molecules into smaller ones, releasing energy in the process, while anabolism refers to the synthesis of larger molecules from smaller ones, requiring energy. Therefore, when discussing the breakdown of substances to produce energy, it is the catabolic aspect of metabolism that is being referred to.

In contrast, synthesis is the process of combining simpler substances to form more complex substances, not focused on energy production through breakdown. Necrosis refers to the death of cells or tissues in the body and is not a chemical process aimed at producing energy. The option that includes all of the above incorrectly suggests that all listed processes involve the breakdown of substances for energy, which is not accurate. Hence, metabolism stands out as the correct choice reflecting the specific energy-producing breakdown process.