Oxygen is an essential requirement for aerobic respiration, but it enters the respiratory process at the end. Discuss.

(N/A) In aerobic respiration, $O_{2}$ acts as the final electron acceptor in the Electron Transport System $(ETS)$.
Although the entire process of respiration involves glycolysis, the Krebs cycle, and the $ETS$, $O_{2}$ is specifically required at the very end of the $ETS$.
It combines with electrons and protons $(H^{+})$ to form water $(H_{2}O)$.
By removing electrons from the last cytochrome $(Cyt a_{3})$, $O_{2}$ allows the continuous flow of electrons through the $ETS$, which is essential for the generation of the proton gradient required for $ATP$ synthesis via oxidative phosphorylation.
Without $O_{2}$, the $ETS$ would stop, leading to the accumulation of reduced coenzymes ($NADH$ and $FADH_{2}$) and the cessation of $ATP$ production.