Which statement about energy use in biological systems is true?

• A. The degradation of complex molecules releases energy that can drive synthesis of other molecules.
• B. Energy is never lost as heat in metabolism.
• C. Organisms require energy only for heat production, not for anabolic processes.
• D. Energy is stored exclusively in DNA.

Answer: (A)

Energy in cells flows from breaking down large molecules to building new ones. When complex molecules are degraded, the energy stored in their chemical bonds is released and captured in energy carriers like ATP. That captured energy is then used to power the synthesis of new molecules, transport work, muscle movement, and other cellular processes. Some energy is inevitably lost as heat, but enough energy is captured to drive anabolic reactions, so the statement that degradation of complex molecules releases energy that can drive synthesis of other molecules is the accurate description.

Why the other ideas don’t fit: energy is not never lost as heat—metabolism produces heat as a byproduct of energy transformations. organisms do require energy for anabolic (biosynthetic) processes, not just for heat production. energy isn’t stored exclusively in DNA; DNA stores genetic information, while energy is stored in molecules like ATP and other high-energy carriers.