Facultative

Facultative means "optional" or "discretionary" (antonym obligate), used mainly in biology in phrases such as:

• Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production
• Facultative biped, an animal that is capable of walking or running on two legs as well as walking or running on four limbs or more, as appropriate
• Facultative carnivore, a carnivore that does not depend solely on animal flesh for food but also can subsist on non-animal food. Compare this with the term omnivore
• Facultative heterochromatin, tightly packed but non-repetitive DNA in the form of Heterochromatin, but which can lose its condensed structure and become transcriptionally active
• Facultative lagoon, a type of stabilization pond used in biological treatment of industrial and domestic wastewater
• Facultative parasite, a parasite that can complete its life cycle without depending on a host
• Facultative photoperiodic plant, a plant that will eventually flower regardless of night length but is more likely to flower under appropriate light conditions

See also

• (antonym) Obligate