Read RQ as a Clue to the Fuel
Respiratory quotient (RQ) is carbon dioxide released divided by oxygen consumed; it depends on the fuel and pathway.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
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Carbohydrate oxidation typically has RQ near 1. Fat oxidation has RQ below 1 because it consumes proportionally more oxygen; organic acids can have RQ above 1. Protein RQ is generally below 1 and varies with the substrate.
Read statements carefully
Cells may oxidise carbohydrate, fats and proteins at the same time. Respiratory substrates need processing: fatty acids undergo β-oxidation and amino acids are deaminated. Avoid absolute claims such as ‘only glucose is respired.’
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- ✓RQ = CO2 released / O2 consumed.
- ✓Carbohydrate ≈ 1; fat < 1; organic acids often > 1.
- ✓More than glucose can fuel aerobic respiration.
A low RQ does not mean the substrate cannot be respired; it reflects its gas-exchange ratio.
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