Which statement best explains the relationship between the electron transport chain (ETC) and redox reactions in microbial metabolism?

The ETC functions by creating ATP directly from redox reactions without proton gradients.

The ETC involves a series of redox reactions that pump protons across a membrane, generating a proton motive force used to synthesize ATP.

The ETC is only used during fermentation and not during respiration.

The ETC bypasses redox reactions by using ATP hydrolysis to generate a proton gradient.