Biology · Respiration in Plants · NEET
RQ is always CO2 evolved on top and O2 consumed on the bottom: RQ = CO2 / O2. Remember 'Released over Required' — the gas Released (CO2) is divided by the gas Required (O2). Flipping it is the most common mistake and gives a wrong answer in the exam.
When a carbohydrate like glucose is fully oxidised, the reaction is C6H12O6 + 6O2 -> 6CO2 + 6H2O. Here 6 molecules of O2 are used and 6 molecules of CO2 are released. So RQ = 6/6 = 1. Equal gases in and out means RQ equals one.
Yes. Organic acids like malic acid have RQ greater than 1 because they already contain a lot of oxygen, so their oxidation releases more CO2 than the O2 taken in. Fats give RQ less than 1, carbohydrates give RQ = 1, and proteins give about 0.9.
RQ tells us which respiratory substrate (food type) is being used. RQ = 1 points to carbohydrate, about 0.7 points to fat, and about 0.9 points to protein. So from one number you can identify the fuel the cell is burning.
RQ is defined for aerobic respiration, where both O2 is consumed and CO2 is released. In pure anaerobic respiration or fermentation, no O2 is used, so RQ becomes infinite (or undefined) because you would divide by zero.
RQ is measured using a Ganong's respirometer. It compares the CO2 given out with the O2 taken in by germinating seeds. NCERT does not ask the apparatus in detail, but it is worth knowing the ratio it measures.
Respiratory Quotient (RQ) value of tripalmitin is
2(C51H98O6) + 145 O2 -> 102 CO2 + 98 H2O + energy. The Respiratory Quotient (RQ) of the biomolecule used for respiration, as per the above equation, would be:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the ratio of CO2 gas released to O2 gas used up during respiration: RQ = CO2 / O2. It tells you which food type the cell is burning.
The RQ of carbohydrates is 1, because equal volumes of CO2 are released and O2 are consumed when a carbohydrate is fully oxidised.
Fats have an RQ less than 1, about 0.7 (for example tripalmitin = 102/145 = 0.7), because their oxidation needs extra O2.
RQ is a direct, high-frequency NEET topic. It links the substrate (carbohydrate, fat, protein) to a single number, and NEET often gives an equation and asks you to calculate or interpret the RQ.
RQ is infinite (undefined) in anaerobic respiration where no O2 is used. It is not zero in normal respiration because CO2 is always released.
