What causes the proton gradient in the electron transport chain?

The correct answer is the pumping of protons (H+) across the inner mitochondrial membrane, which is a fundamental process in the electron transport chain (ETC). As electrons are transferred through a series of protein complexes in the inner mitochondrial membrane, their energy is used to actively transport protons from the mitochondrial matrix into the intermembrane space. This active transport creates a higher concentration of protons in the intermembrane space compared to the matrix, establishing a proton gradient.

This proton gradient is crucial because it represents potential energy that can be harnessed to produce ATP. Protons will naturally want to flow back into the matrix where their concentration is lower, and this movement drives ATP synthase, an enzyme that catalyzes the formation of ATP from ADP and inorganic phosphate.

In contrast, the consumption of oxygen during cellular respiration is an important aspect of the process, as oxygen acts as the final electron acceptor in the electron transport chain. However, oxygen itself does not directly create the proton gradient; rather, it is involved in the overall reaction but does not account for the proton pumping.

The breakdown of glucose into carbon and hydrogen plays a role in providing the electrons that enter the electron transport chain, but this process does not directly create the proton gradient