12.3 Anaerobic respiration

Anaerobic respiration as chemical reactions in cells that break down glucose without oxygen, releasing much less energy than aerobic respiration. Two pathways: yeast (glucose → alcohol + CO₂ — basis of bread, beer) and muscle during vigorous exercise (glucose → lactic acid — the burn). HL extends to the balanced chemical equation for yeast (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂), the build-up of lactic acid causing oxygen debt, and the three-step removal mechanism (fast heart rate transports lactic acid to liver, deeper breathing supplies O₂, liver aerobically respires lactic acid).