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RQ Values of Carbohydrates, Fats and Proteins

Biology · Respiration in Plants · NEET

Respiratory Quotient (RQ) is the ratio of CO2 released to O2 used during respiration. For carbohydrates RQ = 1, for fats RQ is less than 1 (tripalmitin = 0.7), and for proteins RQ is about 0.9. Memory hook: "Carbs = 1, Fat is Fewer (below 1), Protein is Point-nine."
RQ = Volume of CO2 released / Volume of O2 used1.0CarbohydrateRQ = 1ProteinRQ = 0.9FatRQ = 0.7Less oxygen in substrate means more O2 needed, so lower RQ
RQ falls as the substrate carries less oxygen: carbohydrates = 1, proteins about 0.9, fats about 0.7. Fats need the most extra O2, so they have the lowest RQ.

Your doubts, answered

Why is the RQ of carbohydrates exactly 1?

In a carbohydrate like glucose, the amount of oxygen released as CO2 equals the amount of O2 taken in. The equation is C6H12O6 + 6O2 to 6CO2 + 6H2O. Here 6 CO2 are given out and 6 O2 are used, so RQ = 6/6 = 1. Glucose already carries enough oxygen inside it, so it needs less extra O2.

Why is the RQ of fats less than 1?

Fats have very little oxygen and a lot of carbon and hydrogen. So when a fat is oxidised, the cell must take in extra O2 from outside to burn all that hydrogen and carbon. More O2 is consumed than CO2 released, so the ratio (CO2/O2) becomes less than 1. For tripalmitin the value works out to 102/145 = 0.7.

What is the RQ of proteins?

For proteins the RQ is about 0.9. Proteins have less oxygen than carbohydrates but more than fats, so their value sits between fat and carbohydrate. NCERT gives it as approximately 0.9. Remember: proteins are almost never used alone as a respiratory substrate.

Do plants really use pure fat or pure protein for respiration?

No. NCERT clearly states that in living organisms respiratory substrates are often more than one, and pure proteins or pure fats are never used as respiratory substrates. So the real RQ of a cell is usually a mixed value, not exactly 1, 0.7 or 0.9.

When is RQ more than 1?

RQ becomes more than 1 when organic acids are used as substrate, or in germinating seeds and tissues doing partial or anaerobic respiration where CO2 is released without using O2. This is not in the basic carbohydrate/fat/protein list but is a common trap in NEET options.

⚠️ The NEET trap
✗ Thinking fat has a high RQ because fat stores a lot of energy.
✓ Fat has a LOW RQ (about 0.7). High energy does not mean high RQ. RQ depends only on the CO2/O2 ratio, and fats need extra O2, so their RQ is below 1.
🧠 More energy is not more RQ. Fat = low RQ (0.7).

Real NEET questions

NEET 2019

Respiratory Quotient (RQ) value of tripalmitin is

A · 0.9
B · 0.7 ✓
C · 0.07
D · 0.09
Solution: Tripalmitin is a fat. Fats have little oxygen, so their oxidation uses more O2 than the CO2 released, giving RQ below 1. NCERT works it out as RQ = 102/145 = 0.7. Carbohydrates give RQ = 1 and proteins about 0.9.
NEET 2026

2(C51H98O6) + 145 O2 to 102 CO2 + 98 H2O + energy. The Respiratory Quotient (RQ) of a biomolecule used for respiration, as per the above equation would be:

A · Between 0.5 and 0.95 ✓
B · Less than 0.5
C · 1.0
D · Between 1.25 and 2
Solution: RQ = CO2 evolved / O2 consumed = 102/145 = 0.70. A value near 0.7 means a fat (here tripalmitin) is the substrate, and 0.70 lies between 0.5 and 0.95. It is not 1.0 (carbohydrate) and not above 1.

Solved Respiration in Plants NEET PYQs

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Frequently asked

What is the RQ of carbohydrates, fats and proteins?

Carbohydrates = 1, fats = less than 1 (tripalmitin 0.7), proteins = about 0.9.

Which substrate has RQ equal to 1?

Carbohydrates (like glucose) have RQ = 1 because CO2 released equals O2 used.

Which substrate has the lowest RQ?

Fats have the lowest RQ, about 0.7, because they need extra O2 for complete oxidation.

Is protein RQ higher or lower than fat?

Protein RQ (about 0.9) is higher than fat (0.7) but lower than carbohydrate (1).

Why is RQ important for NEET?

NEET often asks direct RQ values or gives an equation like tripalmitin to calculate. Knowing carbs = 1, fat = 0.7, protein = 0.9 helps you answer quickly.

Related concepts:
What is Respiratory Quotient (RQ)?RQ Calculation for Fats: Tripalmitin ExampleWhat are Respiratory Substrates?How Fats and Proteins Enter the Respiratory PathwayWhy the Respiratory Pathway is Amphibolic
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Respiration in Plants PYQs