Anaerobic

Anaerobic describes organisms, processes, or conditions that do not require molecular oxygen or occur in its absence. Some anaerobic organisms are harmed by oxygen, while others tolerate it.

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Anaerobic respiration: Cellular respiration that uses an electron acceptor other than oxygen. It shows how some anaerobic organisms conserve energy through an electron transport chain.
Obligate anaerobe: An organism that cannot grow in the presence of oxygen. This is the strictest form of anaerobic life.
Anaerobic digestion: Microbial breakdown of organic matter without oxygen, producing biogas and digestate. It applies anaerobic metabolism to waste treatment and renewable energy.
Anoxia: A condition in which oxygen is entirely absent from an environment or tissue. It names a strict oxygen-free condition in which anaerobic processes may occur.
Fermentation: A metabolic process that regenerates NAD⁺ by transferring electrons to organic molecules. It lets cells keep producing ATP without relying on oxygen as a terminal electron acceptor.
Facultative anaerobe: An organism that can grow with or without oxygen, often using oxygen when available. It shows that anaerobic growth need not mean oxygen intolerance.
Biogas: A gas mixture, mainly methane and carbon dioxide, produced by microbial breakdown of organic matter. It is a useful product of anaerobic digestion.
Hypoxia: A condition in which oxygen availability is below the level needed for normal function. It describes oxygen shortage rather than the absence of oxygen required by anaerobic conditions.
Glycolysis: A pathway that breaks glucose into pyruvate while producing ATP and NADH. It supplies ATP directly and feeds fermentation when oxygen is unavailable.
Aerotolerant anaerobe: An organism that does not use oxygen for growth but tolerates its presence. It separates oxygen tolerance from oxygen use.