Final answer:
Electrons move through the respiratory enzyme complexes in a process called the electron transport chain, releasing energy to pump protons and create an electrochemical gradient for ATP synthesis, with oxygen as the final electron acceptor resulting in water formation.
Step-by-step explanation:
When electrons move through the electron carriers of the respiratory enzyme complexes, they take part in a series of redox reactions within the electron transport chain (ETC). Starting with complex I, electrons from NADH are passed to coenzyme Q, and from there to complex III. Electrons then transfer to cytochrome c and finally to complex IV, where they reduce oxygen to form water. Throughout this process, energy is released and used to pump protons (H+) across the inner mitochondrial membrane, creating a gradient used for ATP synthesis through oxidative phosphorylation. Complex II also contributes electrons to coenzyme Q but does not participate in proton pumping.
The ETC is critical in aerobic respiration, as it helps generate a high yield of ATP by using the energy from electron transfer to pump protons and form an electrochemical gradient. This gradient drives the synthesis of ATP as protons flow back through ATP synthase. If oxygen is not present to accept electrons at the end of the chain, the flow of electrons would cease, resulting in a stop in ATP production, explaining the necessity of oxygen in aerobic respiration.