ATP, a higher-energy molecule than ADP, is synthesized from ADP in the electron transport chain. Given that molecules cannot go from a lower energy to a higher energy on their own without an external input of energy, how does the energy for this reaction enter the system?

A. Energy enters the system when NADH and FADH2 carry their high-energy electrons to the electron transport chain where, through chemiosmosis, their energy is used to transport hydrogen ions across the membrane into the intermembrane space, causing the buildup of a charge difference.

B. Energy enters the system when NAD+ and FAD carry their high-energy electrons to glycolysis, where, through kinesis, their energy is used to transport acetyl-CoA across the membrane into the intermembrane space, causing the buildup of a charge difference.

C. Energy enters the system when NADH and FADH2 carry their high-energy electrons to the Calvin cycle where, through chemiosmosis, their energy is used to transport hydrogen ions across the membrane into the intermembrane space, causing a higher concentration of hydrogen ions.

D. Energy enters the system when NAD+ and FAD carry their high-energy electrons to the electron transport chain where, through chemiosmosis, their energy is used to transport hydrogen ions across the membrane into the matrix, causing the buildup of lactic acid.