For aerobic respiration of glucose (C6H12O6), where 6 moles of CO2 are produced and 6 moles of O2 are consumed, the RQ is 1.0. For a specific fatty acid (C18H34O2), 18 moles of CO2 are produced and 25.5 moles of O2 are consumed, resulting in an RQ of approximately 0.7. It's important to memorize that carbohydrates typically have an RQ of 1.0, proteins around 0.9, and lipids around 0.7.

The Respiratory Quotient (RQ) is defined as the mole or volume of carbon dioxide produced during respiration divided by the mole or volume of oxygen used up during respiration in a given period of time. This value is crucial for understanding the type of substrate being metabolized.

RQ values can indicate the primary respiratory substrate being used during different activities. For instance, a person standing might primarily use carbohydrates (RQ 1.0). During a slow jog, muscles might switch to lipids (RQ 0.7). Sprinting can cause the RQ to go above 1.0, suggesting an increase in anaerobic respiration and a decrease in oxygen utilization, as more CO2 is produced relative to oxygen consumed due to the bicarbonate buffer system releasing extra CO2.

The RQ of germinating seeds can be measured using a respirometer. In the first part of the experiment, soda lime is included to absorb CO2. The movement of a liquid droplet towards the seeds indicates oxygen consumption. The volume of oxygen used is calculated from the distance the droplet moves and the radius of the capillary tube (πr²L).

To determine CO2 production, the experiment is repeated without soda lime. In this setup, oxygen consumption causes the droplet to move inwards, but CO2 production pushes it outwards. The net movement is observed. By comparing the droplet movement with and without soda lime, the volume of CO2 produced can be calculated. With oxygen consumption (15.7 mm³) and CO2 production (14.8 mm³), the RQ for the germinating seeds is calculated as 0.94, suggesting the seeds are primarily using proteins or carbohydrates.

Another example demonstrates measuring the RQ of an insect. With soda lime, the droplet moves 8 mm, indicating oxygen consumption. Without soda lime, the net movement is only 2 mm. This difference (8mm - 2mm = 6mm) is attributed to CO2 pushing the droplet. Using the same volume calculation (πr²L), the volume of O2 used is 2.3 mm³ and CO2 produced is 1.7 mm³. The resulting RQ of 0.74 suggests the insect is breaking down more lipids as a source of energy at 32°C.

The RQ value cannot be calculated for anaerobic respiration because oxygen is not used up. For example, in yeast anaerobic respiration, CO2 is produced but O2 consumption is zero, leading to an undefined RQ.