The electron transport chain is a chemical reaction where electrons are transferred from a high-energy molecule to a low-energy molecule. These reactions can be used to convert energy from sunlight in photosynthesis or extract energy from sugars in respiration. The electron transport chain is critical to the production of adenosine triphosphate, or ATP, which is a source of energy for living things.
According to Reference.com, in an electron transport chain, the high-energy molecule that gives up the election is called the donor, while the low-energy molecule that is getting the electron is called the acceptor. These electrons are passed from the donor molecule to the acceptor oxygen molecule through a membrane, creating hydrogen ions that are used in ATP.
These processes occur in the mitochondria of eukaryotic cells, where energy is stored at the cellular level. Although electron transport chains and mitochondria are characteristic of eukaryotic cells, some bacteria and Archaea have similar features. While most ATP is produced using electron transport chains, some simpler organisms produce ATP through fermentation. Glycolysis, or the decomposition of glucose, also produces ATP on a very small scale. The last method of producing ATP is through the Krebs or citric acid cycle, which does not use oxygen.