Grade 11 · Life Sciences
Cellular respiration
Compare aerobic respiration and fermentation, and explain how cells release usable energy.
Aerobic respiration
Glucose is broken down using oxygen, producing carbon dioxide and water. Energy is transferred to ATP. Glycolysis occurs in the cytoplasm; the later aerobic stages take place in mitochondria.
Without oxygen
Fermentation enables glycolysis to continue when oxygen is unavailable. Yeast can produce ethanol and carbon dioxide; muscle cells can form lactate. Fermentation yields much less ATP per glucose than aerobic respiration.
Formula sheet
- C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Worked example
Explain why germinating seeds can warm an insulated container.
- Germinating seeds are living and actively respire.
- Respiration releases energy from stored food.
- Some energy is transferred as heat, warming the container.
Try it yourself
1. Where does glycolysis occur? Check answer
In the cytoplasm.
2. Name the gas released during alcoholic fermentation by yeast. Check answer
Carbon dioxide.
Common mistake: Breathing moves air; cellular respiration releases usable energy within cells.