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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
The key difference
Aerobic respiration uses oxygen and completely breaks down glucose into carbon dioxide and water, releasing a large amount of energy. Anaerobic respiration occurs without oxygen and only partially breaks down glucose, releasing much less energy.
Both aerobic and anaerobic respiration release energy from glucose, but they differ in their oxygen requirements, products, and energy yield. This comparison appears in almost every IGCSE Biology exam, and you need to know the equations, products, and biological significance of each type.
Feature
Aerobic Respiration
Anaerobic Respiration
Oxygen required?
Yes
No
Word equation
glucose + oxygen → carbon dioxide + water
In animals: glucose → lactic acid | In yeast: glucose → ethanol + carbon dioxide
Energy released
Large amount (complete breakdown of glucose)
Much less energy (incomplete breakdown: energy still locked in lactic acid / ethanol)
Continuously in all living cells when oxygen is available
During intense exercise (muscles) or in anaerobic environments (yeast)
Glucose breakdown
Complete
Incomplete: product molecules still contain stored energy
Why Anaerobic Respiration Releases Less Energy
In anaerobic respiration, glucose is only partially broken down. The products (lactic acid in animals, ethanol in yeast) still contain chemical energy locked within their molecular bonds. In aerobic respiration, glucose is completely broken down into carbon dioxide and water, releasing all the stored energy. This is why aerobic respiration releases roughly 19 times more energy per molecule of glucose than anaerobic respiration.
Oxygen Debt
After intense exercise, your muscles may have been respiring anaerobically, producing lactic acid. The lactic acid must be broken down, and this requires oxygen. The extra oxygen needed after exercise to remove the lactic acid is called the oxygen debt. This is why you continue to breathe heavily after you stop exercising: your body is repaying the oxygen debt by breaking down lactic acid in the liver.
Anaerobic Respiration in Yeast (Fermentation)
In yeast, anaerobic respiration is called fermentation. The products are ethanol and carbon dioxide (not lactic acid). This process has important industrial applications:
Bread-making: the carbon dioxide causes dough to rise; the ethanol evaporates during baking
Brewing: the ethanol is the desired product; carbon dioxide creates fizz in beer
Biofuel production: ethanol produced by yeast fermentation can be used as a fuel
Try a comparison question (3 marks)
During a 100 m sprint, a runner's leg muscles respire anaerobically. Explain why the runner continues to breathe heavily after finishing the race. [3]
Show the answer and marking guidance
Anaerobic respiration produces lactic acid in the muscles
Lactic acid must be broken down / oxidised, which requires oxygen
The extra oxygen needed to break down lactic acid is the oxygen debt: heavy breathing supplies this oxygen
Original Cambridge-style practice written for this site.
Common comparison mistakes
When answering a compare question, write matched pairs rather than two separate descriptions.
Writing the wrong anaerobic equation: animals produce lactic acid (not ethanol), yeast produces ethanol + CO₂ (not lactic acid)
Saying anaerobic respiration produces "no energy": it produces less energy, not none
Forgetting that aerobic respiration occurs in the mitochondria (anaerobic occurs only in the cytoplasm)
Confusing oxygen debt with simply being "tired": the oxygen debt specifically refers to the oxygen needed to break down lactic acid