The final electron acceptor in oxidative phosphorylation is molecular oxygen O2 . It plays a crucial role in the production of ATP in the Citric acid cycle, also known as the Krebs cycle or the tricarboxylic acid TCA cycle.During the Citric acid cycle, the high-energy electrons are extracted from the metabolic intermediates and transferred to the electron carriers, nicotinamide adenine dinucleotide NAD+ and flavin adenine dinucleotide FAD , which get reduced to NADH and FADH2, respectively. These high-energy electrons are then passed through a series of protein complexes in the inner mitochondrial membrane, known as the electron transport chain ETC .As electrons move through the ETC, they release energy, which is used to pump protons H+ across the inner mitochondrial membrane, creating an electrochemical gradient. This process is called chemiosmosis. The potential energy stored in this gradient is harnessed by the enzyme ATP synthase, which uses the flow of protons back into the mitochondrial matrix to synthesize ATP from ADP and inorganic phosphate Pi . This process of ATP production is called oxidative phosphorylation.Molecular oxygen O2 acts as the final electron acceptor in the ETC. It accepts electrons from the last protein complex in the chain Complex IV and combines with protons to form water H2O . This step is essential for maintaining the flow of electrons through the ETC and the continuous production of ATP. If O2 is not available to accept electrons, the ETC becomes backed up, and the entire process of oxidative phosphorylation and ATP production comes to a halt.