Final answer:
In the mitochondrion's electron transport chain, the terminal electron acceptor is oxygen (O2). Oxygen's acceptance of electrons allows for the generation of water and is pivotal for ATP production in the process of oxidative phosphorylation.
Step-by-step explanation:
The terminal electron acceptor in the mitochondrion's electron transport chain is O2 (oxygen). When electrons are passed along the electron transport chain within the mitochondrion, they move through a series of redox reactions and protein complexes, gradually losing energy. The final step involves the oxygen molecule accepting the low-energy electrons. This acceptance of electrons by oxygen is crucial for the production of water and the maintenance of the entire process of ATP generation via oxidative phosphorylation. In the absence of oxygen, the electron transport chain would not function, leading to a halting of ATP production and potential cell death due to energy deficiency.