Test: Respiratory Substrates & Respiratory Quotient - NEET MCQ

Respiration is an oxidative process in which repiratory substrates are oxidised to liberate energy inside the living cells. The common respiratory substrates are carbohydrates, proteins, fats and organic acids. The most common respiratory substrates are carbohydrates, proteins, fats and organic acids. The most common respiratory substrate is glucose.

During aerobic respiration O₂ is consumed and CO₂ is released. The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration over a period of time is called as respiratory quotient (RQ) or respiratory ratio.

The respiratory quotient depends upon the type of respiratory substrate used during respiration.

(i) When carbohydrates are used as substrate and are completely oxidized the RQ will be 1, because equal amounts of CO₂ and O₂ are evolved and consumed respectively.

(ii) When proteins are respiratory substrates, the ratio would be about 0.9.

RQ slightly more than unity is found when organic acids are broken down as respiratory substrates under aerobic conditions, e.g., for breakdown of oxalic acid,

Succulents do not evolve carbon dioxide during the night (when their stomata are open) as the same is in carbon fixation. They also change carbohydrates to organic acids which utilise oxygen but do not evolve carbon dioxide.

In anaerobic respiration, there is no consumption of oxygen and carbon dioxide is produced in most of the cases. Therefore, respiratory quotient is infinity. Carb the usual substarte.

Glucose is a monomer that after ingestion, does not gets digested and directly gets absorbed and converted into energy. Therefore, glucose is an instantaneous source of energy.
Protein, fats, and nucleic acid don't get directly converted into energy. So, they are not the instantaneous source of energy. 

When facts are used in respiration, the RQ is less than 1, e.g. for the breakdown of tripalmitin,

Respirometer is an instrument used for measuring rate of respiration and respiratory quotient.

Aerobic respiration is a chemical reaction in which glucose gets oxidise and converted into carbon dioxide and water. The following is the balanced chemical reaction -
C₆H₁₂O₆ ​+ 6O₂ ​→ 6CO₂ ​+ 6H₂O + Energy.

The correct option is 2 i.e., conversion of Succinyl coA to Succinic acid.
During the conversion of succinyl-CoA to succinic acid a molecule of GTP is synthesised. This is a substrate level phosphorylation.
The other 3 steps involve oxidation-reduction reaction where NAD+ is reduced to NADH + H⁺ and one point where FAD⁺ is reduced to FADH2.