Which cellular process does not require oxygen?

Fermentation is a metabolic process that takes place in the absence of oxygen. It allows cells to generate energy in the form of ATP by converting sugars into alcohol or acids, depending on the type of fermentation. This anaerobic process is crucial for organisms that either do not have access to oxygen or prefer to function without it. Unlike aerobic respiration and oxidative phosphorylation, which rely on oxygen to produce ATP efficiently, fermentation provides a backup energy source, albeit much less efficient, allowing cells to continue functioning and producing energy under anaerobic conditions.

In contrast, aerobic respiration and oxidative phosphorylation depend on oxygen as a final electron acceptor in the electron transport chain, making these processes fundamentally reliant on the presence of oxygen for ATP production. Chemiosmosis, while associated with ATP synthesis, is part of both aerobic and anaerobic processes, but when specifically linked to oxidative phosphorylation, it is still reliant on oxygen. Therefore, fermentation stands out as the process that exclusively does not require oxygen.