Final answer:
The electron transport chain (ETC) is located in the inner mitochondrial membrane of eukaryotic cells, and in the cytoplasmic membrane of prokaryotic cells, where it transfers electrons to create a proton gradient used to produce ATP.
Step-by-step explanation:
The electron transport chain (ETC) is a series of protein complexes and small molecules within the inner membrane of mitochondria in eukaryotic cells, and in the cytoplasmic membrane of prokaryotic cells. In this process, electrons are taken from NADH and FADH2, which enter the chain, and as they move through it, their energy levels decrease. The energy released from these electrons is used to pump hydrogen ions (protons) across the membrane, creating a proton gradient. At the end of the ETC, electrons are transferred to molecular oxygen, which, along with protons, forms water. The established proton gradient drives the production of ATP through a process called chemiosmosis, ultimately producing about 34 ATP molecules from this phase of cellular respiration.