NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule.

The question is incomplete, the complete question including the options is:

Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2? a) The H+ gradient made from electron transport using NADH is located in a different part of the mitochondrion than the H+ gradient made using FADH2.

b)Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. c)It takes more energy to make ATP from ADP and Pi using FADH2 than using NADH.

d)There is more NADH than FADH2 made for every glucose that enters cellular respiration.

e)FADH2 is made only in the citric acid cycle while NADH is made in glycolysis, acetyl CoA formation, and the citric acid cycle.

The answer is B

Explanation:

Oxidative phosphorylation is the third step of aerobic cellular respiration in living cells. It involves two distinct processes namely: ELECTRON TRANSPORT CHAIN and CHEMIOSMOSIS. The ETC involves transfer of electrons from one molecule to another, leading to the formation of a proton pump (gradient) that will be used to power ATP synthesis.

NADH and FADH2 molecules (reduced electron carriers) produced during the Kreb cycle (second step of cellular respiration) are the first donors of electrons in the ETC. However, both electron carriers do not produce the same amount of ATP at the end of the ETC.

This is because NADH molecules are very good electron donors, hence it starts transferring its electrons directly from Complex I of the ETC. This allows it to pump more protons into the intermembrane space of the mitochondrion. On the other hand, FADH2 molecules cannot transfer its electrons to Complex I of the ETC due to its poor donating ability. Hence, fewer protons are pumped into the mitochondrial intermembrane space.

At the end, 3 and 2 molecules of ATP are produced when NADH and FADH2 are the electron carriers respectively.

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