Respiration In Plants

The respiratory quotient (RQ) and its dependence on substrate are explained in NCERT Class 11, Chapter 14 (Respiration in Plants). RQ is defined as the ratio of the volume of carbon dioxide evolved to the volume of oxygen consumed during respiration. When carbohydrates such as glucose are the respiratory substrate, the balanced equation shows six molecules of carbon dioxide released for every six molecules of oxygen used, so the ratio 6/6 equals one. Therefore a carbohydrate-rich germinating seed respiring aerobically has an RQ of approximately one. The value zero point seven is characteristic of fats, which require more oxygen per carbon dioxide released because they are highly reduced, so it does not apply here. Zero point nine is typical of proteins, again not carbohydrates. \infty corresponds to anaerobic respiration or fermentation where carbon dioxide is released without oxygen being consumed, but the question specifies aerobic respiration. A numerical sanity check confirms the answer: with carbon dioxide output equal to oxygen uptake in carbohydrate oxidation, the quotient must be exactly one, and any measured deviation would signal that a different substrate or an anaerobic pathway was contributing.