Answer:
Sugar
Step-by-step explanation:
The correct answer would be sugar.
Respiration generally involves the metabolic breakdown of carbohydrates to generate energy (in the form of ATP). It is a multi-step process that can summarily be represented by the equation below:
As a rule of thumb, the higher the respiratory quotient of a substrate, the higher the energy that will be generated if such a substrate is utilized for respiration. By definition, the respiratory quotient of a substrate is the ratio of carbon dioxide to oxygen produced or consumed to breakdown the substrate.
Carbohydrates are known to have the highest respiratory quotient while other molecules follow in varying degrees. Other substances apart from carbohydrates have to undergo one or two metabolic processes before they can enter the respiratory pathway, thereby reducing their efficiencies when compared to carbohydrates.