A group of compounds that pass electron from one to another via redox reactions coupled with the transfer of proton across a membrane to create a proton gradient that drives ATP synthesis.
The major role of electron transport chain is to extract energy via redox reactions in cellular respiration and photosynthesis.
In eukaryotes, the electron transport chain can be found in the inner mitochondrial membrane where it serves as the site of oxidative phosphorylation. It is also found in the thylakoid membrane of the chloroplast in photosynthetic organisms.
In bacteria, the electron transport chain is located in their cell membrane.