IGCSE Biology glossary
Lactic acid
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Definition
The waste product of anaerobic respiration in animals. When muscles do not receive enough oxygen during intense exercise, glucose is partially broken down to lactic acid, which accumulates in muscles causing fatigue and cramp.
What to include in an exam answer
Lactic acid is the anaerobic product in ANIMALS, not plants or yeast. For yeast, the products are ethanol and carbon dioxide. This distinction is commonly tested.
Example in context
Explain why muscles produce lactic acid during vigorous exercise (2 marks): During intense exercise, oxygen cannot be supplied to muscles fast enough for aerobic respiration. The muscles respire anaerobically, breaking down glucose incompletely to produce lactic acid.
Related syllabus topic
Respiration