How does cellular respiration work?
Cellular respiration transfers chemical energy from nutrients into forms cells can use through controlled reactions. Oxygen is the final electron acceptor in aerobic respiration. The process is connected to breathing but is not the same as ventilation.
From glycolysis to electron transport
Glycolysis converts glucose into smaller molecules in the cytosol. In eukaryotes, many later steps occur in mitochondria, where the citric acid cycle supplies electron carriers. An electron transport chain establishes a proton gradient across the inner membrane, and ATP synthase uses that gradient. Bacteria can respire using membrane systems despite lacking mitochondria. The process is not a single simultaneous combustion event.
Yield and biological variation
ATP yield varies with cell type, transport costs, and conditions, so one fixed number should not be treated as universal. Fats and some amino acids can also enter energy metabolism through appropriate pathways. Plants respire during both day and night. Fermentation offers a different way to sustain electron-transfer balance and does not provide the same yield as complete aerobic respiration.