Cellular respiration requires energy from an organic source, such as glucose and oxygen, to take place. Cellular respiration is the process by which energy is harvested from an organic source and then stored in the form of ATP to later carry out reactions in the cell. Without the organic source of energy, the reactions cannot take place. Oxygen is needed to serve as the final electron acceptor in electron transport.
Three stages exist in electron transport: glycolysis, the citric acid cycle and electron transport. Cellular respiration takes place in both prokaryotic and eukaryotic organisms. It is considered the most efficient way for an organism to capture energy from food and store it in its cells. The first step of cellular respiration is glycolysis. The term glycolysis literally means splitting sugar. During the process, a molecule of glucose is broken down to yield ATP, pyruvic acid and NADH. The citric acid cycle of cellular respiration takes place when oxygen is present, although oxygen is not used. It produces ATP, NAD and FAD. The electron transport process consists of using oxygen to accept electrons, producing molecules of ATP while doing so. In total, cellular respiration yields 38 molecules of ATP in prokaryotic cells and 36 molecules of ATP in eukaryotic cells.