Anaerobic respiration
Anaerobic respiration is cellular respiration that makes ATP with an electron transport chain but uses a final electron acceptor other than oxygen.
What anaerobic respiration is
Anaerobic respiration is a way for cells to harvest energy when oxygen is unavailable or not used. Electrons from food or other energy-rich molecules move through an electron transport chain, and the cell uses that flow to make ATP.
The final acceptor changes
In aerobic respiration, oxygen is the final electron acceptor. In anaerobic respiration, a different chemical accepts the electrons at the end of the chain. Microbes may use nitrate, sulfate, sulfur, ferric iron, fumarate, carbon dioxide, or other compounds depending on their enzymes and environment.
Why it still makes ATP
The key machinery is a membrane and an electron transport chain. As electrons move through the chain, cells can pump ions across the membrane and create an electrochemical gradient. ATP synthase then uses that gradient to make ATP, much as it does in aerobic respiration.
How it differs from fermentation
Fermentation also works without oxygen, but it is not the same process. Fermentation regenerates electron carriers by passing electrons to organic molecules such as pyruvate or acetaldehyde. Anaerobic respiration keeps a respiratory chain and uses an outside electron acceptor, often an inorganic one.
Where it happens
Anaerobic respiration is common in oxygen-poor habitats: waterlogged soils, sediments, wetlands, animal guts, sewage treatment systems, aquifers, and deep subsurface environments. It is especially important for bacteria and archaea, though the exact chemistry varies widely.
Examples in biogeochemical cycles
Different forms of anaerobic respiration help move nitrogen, sulfur, iron, and carbon through ecosystems. Denitrifying microbes can use nitrate, sulfate-reducing microbes can produce hydrogen sulfide, and methanogens use carbon dioxide or related compounds in methane-producing pathways.
Energy tradeoffs
Oxygen is a very strong electron acceptor, so aerobic respiration often yields more energy. Anaerobic respiration can still be efficient enough to support growth, especially where oxygen is absent but alternative electron acceptors are available.
Why it matters
Anaerobic respiration explains how life thrives in places without oxygen. It shapes soil chemistry, wastewater treatment, greenhouse-gas production, nutrient cycling, corrosion, mineral formation, and the microbial ecology of sediments and wetlands.