What is the primary source of energy utilized by body cells?

Glucose serves as the primary source of energy for body cells because it is a simple sugar that is readily metabolized to produce ATP (adenosine triphosphate), which is the energy currency of the cell. When cells need energy, they break down glucose through processes such as glycolysis and oxidative phosphorylation. This allows for quick access to energy, especially during activities that require sudden bursts of strength or endurance.

While fatty acids and proteins can also serve as energy sources, they are typically utilized under different circumstances. Fatty acids are primarily used when glucose levels are low, such as during prolonged exercise or fasting, and their metabolism is more complex and slower compared to glucose. Proteins can be broken down into amino acids, which may eventually contribute to energy production, but this occurs mainly when carbohydrate sources are insufficient.

Additionally, amino acids are predominantly used for tissue repair and growth rather than as a primary energy source. Thus, although all the options provided can contribute to energy production in varying contexts, glucose is the most efficient and preferred substrate for immediate energy needs in most cells.