What is aerobic respiration?
Aerobic respiration is the breakdown of glucose using oxygen to release energy. Glucose is completely oxidised into carbon dioxide and water, and a large amount of energy is transferred to ATP (about 38 ATP per glucose molecule).
Key idea
Word equation: glucose + oxygen → carbon dioxide + water + energy (ATP).
Symbol equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy.
The stages
- Glycolysis (in the cytoplasm): glucose is split into two pyruvate molecules, producing a small amount of ATP. No oxygen is needed here.
- Krebs cycle (in the mitochondria): pyruvate is broken down, releasing carbon dioxide and energy carriers.
- Electron transport chain (in the mitochondria): oxygen accepts electrons and most of the ATP is made; water is formed.
Why it is efficient
Because glucose is broken down completely, aerobic respiration releases far more energy than anaerobic respiration. This is why active tissues, such as heart and muscle, are rich in mitochondria.
Comparing the energy yield
The big advantage of aerobic respiration is its high energy yield. A single glucose molecule releases about 38 ATP when broken down aerobically, but only about 2 ATP when broken down anaerobically. This is because oxygen allows glucose to be oxidised all the way to carbon dioxide and water, extracting nearly all its chemical energy. Organisms that are very active, such as birds and mammals, rely mainly on aerobic respiration and have many mitochondria in their most active cells to meet their high energy demand.
Example
During light, steady exercise like jogging, your muscles receive enough oxygen to respire aerobically. Glucose is fully broken down to carbon dioxide and water, giving a steady, efficient supply of ATP and no build-up of lactic acid.
Remember
Aerobic = with oxygen, complete breakdown, products CO2 + water, ~38 ATP. Learn the balanced equation: glucose + 6O2 → 6CO2 + 6H2O.