Biology
Cellular respiration — quick study summary
AP BiologyGCSE BiologyIB Biology HL
Cellular respiration converts glucose into ATP, the energy currency of the cell. It runs in four stages: glycolysis in the cytosol, pyruvate oxidation and the Krebs cycle in the mitochondrial matrix, and the electron transport chain on the inner mitochondrial membrane. Aerobic respiration produces ~30–32 ATP per glucose.
Key points
- Overall: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~30–32 ATP
- Glycolysis: glucose → 2 pyruvate, net 2 ATP and 2 NADH
- Krebs cycle: per glucose makes 6 NADH, 2 FADH₂, 2 ATP, 4 CO₂
- Electron transport chain uses NADH/FADH₂ to pump H⁺ for ATP synthase
- Without O₂, cells switch to fermentation (lactate or ethanol)
Practice quiz
Click each question to reveal the answer.
1. Where does glycolysis take place?
- Mitochondrial matrix
- Cytosol
- Nucleus
- Endoplasmic reticulum
Answer: Cytosol
2. What is the final electron acceptor in aerobic respiration?
Answer: Oxygen
Oxygen accepts electrons at the end of the electron transport chain, forming water.
3. How many net ATP does glycolysis produce per glucose?
Answer: 2
Last reviewed: May 2026