Final answer:
NADH and FADH2 give up electrons to the electron transport chain in the inner mitochondrial membrane, where oxygen ultimately accepts them to form water. This process pumps hydrogen ions across the membrane, creating a gradient that leads to ATP synthesis.
Step-by-step explanation:
NADH and FADH2 are important electron carriers in the electron transport chain (ETC) of cellular respiration. The electrons are released from NADH and FADH2 and eventually accepted by oxygen to form water. This series of oxidation-reduction reactions occurs in the inner membrane of the mitochondrion. Each carrier in the chain is reduced when it receives an electron and oxidized when it passes the electron to the next carrier.
The energy released during these electron transfers is used to pump hydrogen ions across the mitochondrial inner membrane, from the matrix into the intermembrane space, creating a proton gradient. This proton gradient then drives ATP synthesis through ATP synthase, a process known as oxidative phosphorylation. The initial electron acceptor for electrons from NADH is flavin mononucleotide (FMN), while electrons from FADH2 enter the ETC at Complex II and then proceed to Complexes III and IV, finally being transferred to oxygen at Complex IV.