Lesson 10 of 11 · 10 min
Respiratory quotient
NCERT §12.7
Kavya measures the gases around two sets of germinating seeds, rice and groundnut, and finds that they do not trade oxygen for carbon dioxide one for one.
The lesson in notes
In short
The respiratory quotient (RQ), also called respiratory ratio, is the volume of CO₂ evolved divided by the volume of O₂ consumed in respiration.
RQ depends on which substrate is being respired.
Carbohydrates completely oxidised give RQ = 1: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy, so RQ = 6CO₂ / 6O₂ = 1.0.
Fats give RQ below 1. For tripalmitin, 2(C₅₁H₉₈O₆) + 145O₂ → 102CO₂ + 98H₂O + energy, so RQ = 102CO₂ / 145O₂ = 0.7.
Proteins as substrate give an RQ of about 0.9.
In living organisms more than one substrate is usually respired at a time; pure proteins or pure fats are never the only substrate.