12.4 Oxygen Debt & The Liver
The Recovery Process After Anaerobic Exercise
Syllabus Focus (12.3.7 Supplement): Understand that oxygen debt is the volume of oxygen needed to break down lactic acid, and learn the three-part recovery system involving the heart, lungs, and liver working together to remove lactic acid through aerobic respiration.
What is Oxygen Debt?
Oxygen Debt is the volume of oxygen needed to completely break down the lactic acid that built up in muscles during anaerobic respiration.
Oxygen Debt = Extra O₂ needed to oxidize all the lactic acid
The Three-Part Recovery System
1. Heart Continues Beating Fast
Pumps blood to transport lactic acid from muscles to the liver
2. Lungs Continue Breathing Deep & Fast
Supply the extra oxygen needed by the liver to break down lactic acid
3. Liver Performs Aerobic Respiration
Oxidizes lactic acid using oxygen from the lungs
Lactic Acid + O₂ → CO₂ + H₂O + Energy
(Energy used to convert some lactic acid back to glucose)
Common Questions About Recovery
Why is my heart still racing after I stop running?
Why am I still breathing heavily after exercise?
What is oxygen debt?
What happens to lactic acid in the liver?
EXAMINER TRAP: Common Mistakes
- ✗Saying "oxygen debt breaks down lactic acid" - NO! The liver breaks it down using oxygen
- ✗Forgetting the liver's role - lactic acid isn't broken down in muscles
- ✗Not mentioning that heart and lungs work after exercise stops
- ✓CORRECT: "The liver uses oxygen from breathing to perform aerobic respiration on lactic acid, producing CO₂, water, and energy (or glucose)"
Cambridge IGCSE Biology 0610 | Supplement Content Only
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