Which process during cellular respiration directly relies on the presence of oxygen?
A citric acid cycle
B the electron transport chain
C glycolysis
D the formation of acetyl
The correct answer and explanation is:
The correct answer is B: the electron transport chain.
During cellular respiration, oxygen plays a critical role specifically in the electron transport chain (ETC). The ETC is the final stage of aerobic respiration and takes place in the inner mitochondrial membrane. This process involves a series of protein complexes and electron carriers that transfer electrons derived from NADH and FADH2 to oxygen.
Oxygen acts as the final electron acceptor in the chain. At the end of the ETC, electrons combine with oxygen and protons (hydrogen ions) to form water. Without oxygen, electrons cannot be passed along the chain, causing the ETC to halt. When the ETC stops functioning, the proton gradient across the mitochondrial membrane collapses, stopping ATP production by oxidative phosphorylation. This makes oxygen essential for efficient energy production in aerobic respiration.
In contrast, the other processes listed do not directly require oxygen. Glycolysis (option C) takes place in the cytoplasm and breaks glucose into pyruvate, producing a small amount of ATP and NADH. It does not require oxygen and can occur anaerobically. The citric acid cycle (option A), also called the Krebs cycle, occurs in the mitochondrial matrix and processes acetyl-CoA to produce NADH and FADH2, but it depends indirectly on oxygen because its products feed into the ETC, which requires oxygen to function. The formation of acetyl-CoA (option D) is an intermediate step converting pyruvate into acetyl-CoA before entering the citric acid cycle, and it also does not require oxygen directly.
In summary, oxygen is essential for the electron transport chain because it accepts electrons at the end of the chain, allowing the continuous flow of electrons and production of ATP. Without oxygen, aerobic respiration cannot proceed efficiently.