Electron donor
An electron donor is a chemical species that gives up electrons in a redox reaction, becoming oxidized while another species is reduced.
What an electron donor is
An electron donor is a substance that gives electrons to another substance during a redox reaction. By donating electrons, it is oxidized. The substance receiving those electrons is the electron acceptor and is reduced.
Donating electrons means being oxidized
Oxidation means loss of electrons. That is why an electron donor is oxidized during the reaction. The donor does not disappear as an idea; it changes chemical form because some of its electrons have moved to an acceptor.
Reducing agents
An electron donor is often called a reducing agent because it reduces another substance by giving it electrons. Hydrogen, organic carbon compounds, sulfide, ferrous iron, ammonia, and many metals can act as reducing agents in the right conditions.
Energy comes from electron transfer
Many living systems use electron donors as energy sources. Cells harvest energy when electrons move from donors to acceptors through enzymes and electron carriers. The amount of usable energy depends on the donor, the acceptor, and the redox gap between them.
Respiration and food
In cellular respiration, food molecules such as glucose are electron donors. Their electrons move through carriers and eventually reach a terminal electron acceptor. In aerobic respiration that acceptor is oxygen, while anaerobic microbes can use other acceptors.
Chemosynthesis without sunlight
Chemosynthetic microbes use inorganic electron donors instead of sunlight as their energy source. At hydrothermal vents or in subsurface environments, compounds such as hydrogen sulfide, hydrogen, methane, or reduced metals can help power microbial growth.
Environmental redox zones
In soils, aquifers, wetlands, and sediments, available electron donors shape microbial activity. Organic matter often supplies electrons as microbes consume it. Reduced minerals or gases can also feed metabolisms that drive denitrification, sulfate reduction, methanogenesis, and other pathways.
Why it matters
Electron donors help explain why fuels burn, batteries work, microbes grow in dark places, metals corrode, and nutrients cycle in oxygen-poor environments. Following the donor shows where electrons start before chemistry, metabolism, or engineering systems put them to work.