Answer:
C. In the third stage, fuel molecules are completely oxidized to CO2 , and most of the ATP needed for cellular processes is produced.
Step-by-step explanation:
The three stages in the generation of energy from the oxidation of foodstuffs are given below:
First stage - This stage is the preparation stage and no useful energy is produced in this stage. In this stage, large molecules in food are broken down into smaller units. Proteins are broken down to amino acids, polysaccharides to simple sugars such as glucose, and fats are broken down to glycerol and fatty acids.
Second stage - In this stage, the various small molecules from the first stage are degraded to simple units (mostly acetyl-CoA) that are useful in metabolic activities of the body. Few ATP molecules are generated in this stage.
Third stage - In this final stage, most of the ATP required for cellular processes is produced from the complete oxidation of the acetyl unit of acetyl CoA to CO₂ in the citric acid cycle as well the oxidation of the electron carriers NADH and FADH₂ in oxidative phosphorylation.