Which processes occur under aerobic conditions?

Under aerobic conditions, cellular respiration processes are designed to maximize ATP production by utilizing oxygen. The correct answer highlights the Citric Acid Cycle and the Electron Transport Chain as key processes that occur when oxygen is present.

The Citric Acid Cycle, also known as the Krebs Cycle, operates in the mitochondria and is responsible for the oxidative degradation of acetyl-CoA to produce NADH and FADH2, both of which are essential for the electron transport chain. This cycle is inherently reliant on aerobic conditions, as it requires oxygen indirectly to regenerate NAD+ through the electron transport chain.

The Electron Transport Chain functions by transferring electrons through a series of protein complexes, which ultimately leads to the formation of ATP via oxidative phosphorylation. Oxygen is the final electron acceptor in this process, enabling the efficient production of ATP. The presence of oxygen allows for the complete oxidation of fuel molecules, yielding a significant amount of energy compared to anaerobic processes.

In contrast, glycolysis occurs in both aerobic and anaerobic conditions, but it does not solely rely on oxygen. Fermentation, meanwhile, is an anaerobic process that allows for the regeneration of NAD+ in the absence of oxygen by converting pyruvate into lactic acid or ethanol, indicating that it does not occur