What term best defines cell respiration?

• A. Release of energy from chemical bonds of food molecules in the form of ATP
• B. The breakdown of proteins into amino acids
• C. The synthesis of ATP from ADP using sunlight
• D. The storage of energy in glycogen

Answer: (A)

The main idea is that cell respiration is how cells release the energy stored in nutrients and capture it as ATP, the energy currency of the cell. In this process, chemical bonds in food molecules are broken to transfer energy into ATP, which powers cellular activities. The typical sequence—glycolysis to break glucose, the citric acid cycle, and the electron transport chain—extracts energy step by step, with oxygen often acting as the final electron acceptor during aerobic respiration. That production of ATP from the nutrient energy is the essence of respiration.

Other options describe different concepts: breaking down proteins into amino acids is digestion and protein metabolism, not respiration; synthesizing ATP from ADP using sunlight is photosynthesis; storing energy in glycogen is about energy storage, not the release of energy via respiration.