The correct answer is A.chemical energy in the bonds of food molecules.
The cells require a constant supply of energy to generate and maintain their functions. Sugars are most commonly used as fuel molecules (especially glucose). Food Molecules Are broken down in three stages: the first step is digestion (intestine), second is glycolysis (cytosol) and the third is the citric acid cycle together with oxidative phosphorylation (mitochondria). During the process of oxidative phosphorylation, ATP is produced.
