Which molecule is the most common source of energy for cells?

Glucose is the most common source of energy for cells due to its central role in cellular respiration. It is a simple sugar that serves as a primary energy substrate for most organisms. When glucose is metabolized through glycolysis, it undergoes conversion to pyruvate, which is further processed through the Krebs cycle and oxidative phosphorylation in the mitochondria. This process efficiently generates adenosine triphosphate (ATP), which cells use as an energy currency for various biological functions.

While fructose and galactose can also be utilized by the body for energy, they are typically converted into glucose (or intermediates that enter pathways leading to glucose) before being used in the energy-producing processes. Starch, on the other hand, is a polysaccharide found in plants and is broken down into glucose molecules through digestion before it can be used for energy, making glucose the key molecule derived from starch.

Thus, glucose stands out as the most direct and readily available energy source for cellular metabolism, reinforcing its classification as the primary energy molecule for cells.