Final answer:
NADH and FADH2 are the important elements harvested from glycolysis and the citric acid cycle that feed the electron transport chain, resulting in ATP production through oxidative phosphorylation.
Step-by-step explanation:
The important elements that are harvested from glycolysis and the citric acid cycle (Krebs cycle) and fed to the electron transport chain are NADH and FADH2. During glycolysis, glucose is broken down into pyruvate, with a net production of ATP and NADH. In the presence of oxygen, pyruvate is converted into acetyl-CoA and enters the citric acid cycle. Each turn of the cycle produces three NADH molecules and one FADH2 molecule, as well as releasing carbon dioxide and generating a small amount of ATP (or GTP) directly through substrate-level phosphorylation. The NADH and FADH2 produced carry electrons to the electron transport chain, where they donate electrons to oxygen, the final electron acceptor, resulting in the formation of water. The energy released during the transfer of electrons down the chain is used to pump protons and create a proton gradient. This gradient powers ATP synthesis through oxidative phosphorylation. Ultimately, the high-energy electrons from NADH and FADH2 are crucial for the generation of a large amount of ATP, which is the energy currency of cells.