In electron transport chain, electrons transport through a series of carriers. H+ of NADH+(received from Krebs cycle) is accepted by FAD as a result of which FAD is reduced to FADH+ and NADH+ is oxidised to NAD. Reduced FADH+ is oxidised by CoQ, with the formation of CoQH+,H+ ions then move to Cyt b, then Cyt c, Cyt a and Cyt aa3. Ultimately these H+ are accepted by O2 and H2O is formed.