D

B

The electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions. In eukaryotic cells, the ETC is located in the inner mitochondrial membrane.

The electron flow in the ETC begins with the transfer of electrons from NADH and FADH2 to Complex I (NADH dehydrogenase) and Complex II (succinate dehydrogenase), respectively. From there, the electrons are passed through a series of protein complexes, including Complex III (cytochrome bc1 complex) and Complex IV (cytochrome c oxidase), before ultimately being transferred to oxygen, the final electron acceptor, to form water.

During this process, Complexes I, III, and IV pump protons from the mitochondrial matrix into the intermembrane space, creating an electrochemical gradient. This proton pumping generates a proton motive force, which is used by ATP synthase to produce ATP through oxidative phosphorylation.

In summary, the electron transport chain consists of multiple protein complexes, including Complexes I, III, and IV, which pump protons into the intermembrane space, ultimately leading to the production of ATP.

A

B

True