Define Respiratory Quotient Class 11

Learn about the respiratory quotient and its significance in cellular respiration. Discover how RQ values vary based on substrates and their oxidation levels. Explore examples, case studies, and statistics to understand this vital concept in biology.


Respiratory quotient is a vital concept in biology that helps in understanding the metabolism of an organism. In class 11, students learn about the respiratory quotient and its significance in cellular respiration. Let’s delve deeper into this topic.

What is Respiratory Quotient?

Respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration. It is a measure of the type of fuel being metabolized by an organism. The RQ value varies depending on the type of substrate being oxidized.

Calculating Respiratory Quotient:

RQ = CO2 produced / O2 consumed

Significance of Respiratory Quotient:

  • Helps in determining the type of respiratory substrate being utilized by an organism
  • Provides insights into the efficiency of cellular respiration
  • Aids in understanding the metabolic state of an organism


For carbohydrates, the RQ is close to 1 as they are oxidized completely to CO2 and water. For fats, the RQ is lower than 1 as they are not completely oxidized. Similarly, proteins have an RQ value based on their composition.

Case Studies:

Researchers use respiratory quotient in studies to analyze the metabolic response to different diets and exercise regimens. For instance, a study showed that individuals on a high-protein diet had a lower RQ compared to those on a high-carbohydrate diet, indicating a shift in substrate utilization.


A study conducted on athletes found that their RQ values were lower during exercise, indicating a higher fat utilization for energy production. This showcases the adaptability of metabolism based on the energy demands of the body.


Understanding respiratory quotient is crucial for comprehending the energy metabolism of living organisms. Class 11 students can apply this knowledge in various biological contexts to analyze the metabolic pathways and determine the efficiency of cellular respiration.

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