Microbiology Practice Exam

What is the final electron acceptor in aerobic respiration?

1. Nitrogen

2. Carbon dioxide

3. Oxygen

4. Hydrogen

The correct answer is: Oxygen

In aerobic respiration, oxygen functions as the final electron acceptor. This process occurs in the electron transport chain, a critical stage in cellular respiration. As electrons are transferred through a series of protein complexes embedded in the inner mitochondrial membrane (in eukaryotes) or the plasma membrane (in prokaryotes), they lose energy, which is harnessed to pump protons across the membrane, creating a proton gradient. At the end of this electron transport chain, the electrons are transferred to oxygen, which combines with protons to form water. This step is crucial because it allows the continuous flow of electrons through the chain; without a final electron acceptor like oxygen, the entire process would halt. The other choices do not participate as final electron acceptors in aerobic respiration, as nitrogen is typically involved in nitrogen fixation, carbon dioxide is produced as a waste product of metabolism, and hydrogen does not serve in this capacity.