Botany - Respiration in Plants Question with Solution | TestHub

The value of R.Q. always depends upon the chemical nature of the substrate. In respiration, many types of high energy compounds are oxidized. These are called respiratory substrate or respiratory fuel and include carbohydrates, fats and protein.

Carbohydrates such as glucose, fructose (hexoses), sucrose (disaccharide) or starch, insulin, hemicellulose (polysaccharide), etc; are the main substrates. The energy present in one gram carbohydrate is 4.4 Kcal or 18.4 kJ. Under certain conditions (mainly when carbohydrate reserves have been exhausted) fats are also oxidized. The energy present in one gram of fats is 9.8 Kcal or 41kJ. In the absence of carbohydrates and fats, protein also serves as respiratory substrate. The energy present in one gram of protein is 4.8 Kcal or 20 kJ.