Aerobic Respiration

Aerobic respiration is the process by which cells use oxygen to break down food molecules, mostly glucose, and capture the energy as ATP. The overall reaction is glucose + 6 O₂ → 6 CO₂ + 6 H₂O, and it releases far more energy than fermentation.

The process begins with glycolysis in the cytoplasm, which splits one glucose into two pyruvate molecules. Pyruvate enters the mitochondrion and is converted to acetyl-CoA, which feeds the citric acid cycle, producing carbon dioxide and electron carriers. These carriers deliver electrons to the electron transport chain, which pumps protons, and the resulting gradient drives ATP synthesis in oxidative phosphorylation. Oxygen is the final electron acceptor and combines with them to form water.

A glucose molecule gives roughly 30 to 32 ATP in aerobic respiration, compared with 2 ATP from glycolysis followed by fermentation. The total depends on how many protons are needed per ATP and on the shuttles that move electron carriers into the mitochondrion, and so it is an estimate rather than a fixed number. Bacteria carry out the same process across their plasma membrane.

The reactions are the reverse of photosynthesis, and together they link the carbon and oxygen cycles. Aerobic respiration became widespread after oxygen built up in the Great Oxidation Event, and it supported the evolution of large, active animals. The process is a central subject of cellular respiration and bioenergetics.

• Cellular Respiration — the general process
• Citric Acid Cycle — its central stage
• Photosynthesis — the complementary process