Aerobic Respiration
Aerobic respiration is a catabolic process that occurs in the presence of oxygen, breaking down glucose to produce ATP, carbon dioxide, and water. This process involves three main stages: glycolysis, the Krebs cycle, and the electron transport chain, each occurring in specific locations within the cell.
The overall balanced chemical reaction for aerobic respiration can be summarised as: C6H12O6 + 6O2 → 6CO2 + 6H2O + 36–38 ATP
Glycolysis
Glycolysis occurs in the cytoplasm and is the first step in glucose metabolism. It involves the breakdown of one glucose molecule (C₆H₁₂O₆) into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH molecules. The inputs are glucose and 2 ATP, while the outputs include 2 pyruvate, 4 ATP (net 2 ATP gain), and 2 NADH.
Krebs Cycle
The Krebs cycle takes place in the mitochondrial matrix, where pyruvate is further broken down into carbon dioxide. This cycle generates high-energy electron carriers, specifically NADH and FADH₂, and produces 2 ATP per molecule of glucose.
Electron Transport Chain
The electron transport chain, located in the inner mitochondrial membrane, uses these electron carriers to generate a large amount of ATP—approximately 32–34 molecules—by driving the movement of protons across the membrane, ultimately producing water as oxygen accepts the electrons. The overall inputs of this stage include pyruvate, NAD⁺, FAD, and oxygen, and the outputs are carbon dioxide, water, and approximately 34 ATP.
Comparison of aerobic and anaerobic respiration
Aerobic respiration requires oxygen and yields a high amount of ATP (36–38 ATP per glucose molecule), making it highly efficient. In contrast, anaerobic respiration occurs without oxygen and takes place entirely in the cytoplasm.
It involves only glycolysis, followed by either lactic acid fermentation (in animals) or alcohol fermentation (in yeast and plants). The net ATP yield from anaerobic respiration is significantly lower, producing only 2 ATP per glucose molecule.
Anaerobic respiration also results in by-products such as lactic acid or ethanol and carbon dioxide, which can be harmful if accumulated.
| Feature | Aerobic Respiration | Anaerobic Respiration |
| Oxygen Requirement | Requires oxygen | Does not require oxygen |
| Location in Cell | Mitochondria (Krebs cycle and electron transport chain) and cytoplasm (glycolysis) | Cytoplasm (glycolysis only) |
| Net ATP Production | Approximately 36–38 ATP per glucose molecule | 2 ATP per glucose molecule |
| Primary Reactants | Glucose and oxygen | Glucose |
| Primary Products | Carbon dioxide and water | Lactic acid (in animals) or ethanol and carbon dioxide (in yeast and plants) |
| Efficiency | High (complete oxidation of glucose) | Low (incomplete oxidation of glucose) |
| By-products | Water and carbon dioxide | Lactic acid or ethanol and carbon dioxide |
| Duration | Long-term, used during prolonged exercise and normal cellular processes | Short-term, used during intense exercise or oxygen-limited conditions |