1. Respiratory Quotient (RQ)
  • RQ = volume of CO₂ released ÷ volume of O₂ consumed during aerobic respiration.
  • Carbohydrate: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy, so RQ = 6/6 = 1.0.
  • Lipid (e.g. stearic acid): RQ ≈ 0.7 (fewer oxygen atoms in the substrate relative to carbon, so relatively more O₂ is needed).

Significance of RQ

  • Indicates which substrate is being oxidised: ~0.7 = lipids, ~0.8 = protein, ~1.0 = carbohydrate. RQ also reflects metabolic rate and feeding status — underfeeding (using fat stores) gives RQ < 0.85; overfeeding (lipogenesis) gives RQ > 1.
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