Throughout the series of reactions, CO2 is released and several molecules of NADH or FADH 2 are reduced. These play a critical role in the next stage of respiration, the electron transport chain. These chemical reactions occur in the matrix of the mitochondria. This is where the majority of ATP molecules are synthesized for cellular respiration. Importantly, the mitochondrial membrane is involved with this series of redox reactions.
Oxygen serves as that electron acceptor under aerobic conditions.
When oxygen is not available, the electron transport chain backs up since there is no final electron acceptor. Alcoholic fermentation . Lactic acid fermentation . Pyruvic acid from glycolysis is converted into lactic acid which can be re-converted into pyruvic acid once conditions become more aerobic.