Advanced Placement (AP) Chemistry Practice Exam

The electron transport chain is a crucial component of cellular respiration, specifically during the aerobic process of oxidative phosphorylation. Its primary function is to facilitate the transfer of electrons derived from NADH and FADH₂, which are produced in previous stages of cellular respiration such as glycolysis and the Krebs cycle. These electrons move through a series of proteins embedded in the inner mitochondrial membrane, which helps create a proton gradient across the membrane.

As electrons are passed along the chain, protons (H⁺ ions) are pumped from the mitochondrial matrix into the intermembrane space, generating a proton gradient. This gradient creates potential energy, which is utilized by ATP synthase to synthesize ATP as protons flow back into the matrix. In the final step of the electron transport chain, oxygen acts as the terminal electron acceptor, combining with electrons and protons to form water. This entire process not only produces ATP but also contributes to the overall energy yield of cellular respiration. Thus, the electron transport chain is essential for the efficient production of ATP and water, making option B the correct answer.