The overall process by which cells generate ATP is called cellular respiration. This biochemical process converts biochemical energy from nutrients into ATP, which cells use as a direct energy source for performing various functions. Cellular respiration occurs in several stages: glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain. While the process primarily utilizes glucose, it can also operate on other substrates, like fatty acids and amino acids. Efficient ATP production is vital for maintaining cellular activities and overall organismal energy balance.