Final answer:
NADH is oxidized by complex I of the ETC, while FADH2 is oxidized by complex II. Complex II bypasses complex I, leading to a lower ATP yield from FADH2.
Step-by-step explanation:
The statement that NADH and FADH2 are produced by the citric acid cycle (CAC) and get oxidized by complex I of the electron transport chain (ETC) is partially true and partially false. NADH is indeed oxidized by complex I of the ETC, but FADH2 is oxidized by complex II. Complex II directly receives electrons from FADH2 using the enzyme succinate dehydrogenase, which is part of the citric acid cycle, and delivers these electrons directly to the electron transport chain, bypassing complex I. This results in a lower ATP yield from FADH2 compared to NADH, as FADH2 does not contribute to the proton gradient at complex I. During oxidative phosphorylation, NADH and FADH2 provide energy by donating electrons, which eventually results in the production of ATP.