Positive reduction potential.
Moreover, In aerobic respiration, electrons are transferred along the electron transport chain by the reversible reduction and oxidation of iron-sulfur clusters, ubiquinone (CoQ), cytochromes, and copper ions. Each electron carrier accepts an electron or electron pair from a carrier with a less positive reduction potential and transfers the electron to a carrier with a more positive reduction potential. In this way the reduction potentials of electron carriers drive unidirectional electron flow from NADH and FADH2 to O2.
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