RQ is the mole or volume of carbon dioxide (CO2) produced during respiration divided by the mole or volume of oxygen (O2) used up during the same period.
Two Definitions:
Moles of CO2 produced / Moles of O2 used
Volume of CO2 produced / Volume of O2 used
Examples of RQ Calculation
Aerobic Respiration of Glucose
Chemical Equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O
RQ Calculation:
Moles of CO2 = 6
Moles of O2 = 6
RQ = 6 / 6 = 1.0
Aerobic Respiration of Fatty Acids
Example Fatty Acid: C18H34O2
Requires 25.5 moles of O2; produces 18 moles of CO2
RQ Calculation:
RQ = 18 / 25.5 ≈ 0.7
Memorization of RQ Values
Carbohydrates: RQ ≈ 1.0
Proteins: RQ ≈ 0.9
Lipids: RQ ≈ 0.7
Important to memorize for exams.
RQ and Anaerobic Respiration
RQ cannot be calculated for anaerobic respiration as no O2 is used.
Practical Application: Measuring RQ on a Treadmill
Activities and RQ Observations:
Standing: RQ = 1.0
Slow Jog: RQ = 0.7 (switch to lipid use)
Walking: RQ = 1.0
Sprinting: RQ > 1.0 (anaerobic respiration, less O2 used)
Experiment to Measure RQ
Using Germinating Seeds
Place seeds in a sealed chamber with a capillary tube.
Use soda lime (KOH/NaOH) to absorb CO2.
Measure movement of liquid droplet in the tube to determine oxygen use.
Calculating Volume of Oxygen Used
Distance droplet moves = volume of O2 used
Use formula for volume of a cylinder: πr²L
Example: Radius = 1 mm, Distance = 5 mm
Volume of O2 = π(1²)(5) ≈ 15.7 mm³
Determining Volume of CO2 Produced
Repeat experiment without soda lime.
Measure droplet movement:
Example: Initial movement = 5 mm, Without soda lime = 0.3 mm
Volume of CO2 = πr²(4.7 mm) ≈ 14.8 mm³
Calculating RQ
RQ = Volume of CO2 / Volume of O2
Example: RQ = 14.8 / 15.7 ≈ 0.94
Assumes use of carbohydrates/proteins.
Another Example
With soda lime: Droplet moves 8 mm
Without soda lime: Droplet moves 2 mm
Calculation:
Volume of CO2 = πr²(6 mm) ≈ 1.7 mm³
RQ = 1.7 / 2.3 ≈ 0.74
Assumes use of lipids at 32°C
Conclusion
RQ provides insight into the type of substrate being used in respiration (carbohydrates, proteins, lipids).
Important to understand both theoretical concepts and practical experiments for calculating RQ.