Final answer:
Carbohydrates are the only energy substrates that can be metabolized both aerobically and anaerobically to produce ATP, with glucose being the central molecule used during both processes to generate energy.
Step-by-step explanation:
The only energy substrate that can be metabolized aerobically or anaerobically to produce ATP is carbohydrates. In aerobic respiration, carbohydrates are broken down to produce ATP, NADH, and FADH2, eventually leading to the production of ATP via the electron transport chain using oxygen as the final electron acceptor. In anaerobic conditions, ATP can still be produced through the process of glycolysis, where glucose is converted into pyruvate, yielding ATP even in the absence of oxygen.
Glucose, a simple carbohydrate, is the primary energy source for both types of metabolism. During high-intensity exercises where oxygen levels are insufficient for aerobic metabolism, the body switches to anaerobic metabolism, still relying on glucose to produce ATP. On the other hand, fatty acids primarily fuel aerobic metabolism activities that are lower in intensity and last longer, whereas proteins are not a primary energy source. However, in extreme cases such as long endurance exercises or insufficient caloric intake, proteins may be used to a greater extent.