Obligate means "by necessity" (antonym facultative) and is used mainly in biology in phrases such as:
- Obligate aerobe, an organism that cannot survive without oxygen
- Obligate anaerobe, an organism that cannot survive in the presence of oxygen
- Obligate air-breather, a complex organism which obtains required oxygen directly from the atmosphere through respiration rather than extracting dissolved oxygen from water, as, for example, the South American lungfish
- Obligate carnivore, a true carnivore solely dependent for survival on the nutrients found in animal flesh.
- Obligate intracellular parasite, a parasitic microorganism that cannot reproduce without entering a suitable host cell
- Obligate parasite, a parasite that cannot reproduce without exploiting a suitable host
- Obligate photoperiodic plant, a plant requiring long or short nights before flowering
- Obligate symbionts, organisms which can only live together in a symbiosis
- Obligate hibernation, a state used by some mammals to survive conditions where food is scarce.
See also
- (antonym) Facultative