Final answer:
NADH and FADH2 are the molecules that transport high-energy electrons to the electron transport chain, enabling the synthesis of ATP through oxidative phosphorylation.
Step-by-step explanation:
The molecules responsible for transporting high-energy electrons to the electron transport chain are NADH and FADH2.
NADH and FADH2 are generated during the earlier stages of cellular respiration. They donate their high-energy electrons to the electron transport chain located in the inner membrane of the mitochondrion. Therein, these electrons are transferred through various electron carriers, ultimately to oxygen, the final electron acceptor. As they are passed along the chain, the electron carriers also pump hydrogen ions out of the mitochondrial matrix, helping to build a proton gradient across the inner mitochondrial membrane. This gradient is then utilized by ATP synthase to manufacture ATP in a process known as oxidative phosphorylation.