What is Obligate?

Legal Definition
As an adjective, 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 term used in fish physiology to describe those that respire entirely from the atmosphere
  • Obligate biped, Bipedalism designed to walk on two legs
  • Obligate carnivore, an organism dependent for survival on a diet of animal flesh.
  • Obligate hibernation, a state of inactivity in which some organisms survive conditions of insufficiently available resources.
  • 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 that requires sufficiently long or short nights before it initiates flowering, germination or similarly functions
  • Obligate symbionts, organisms that can only live together in a symbiosis
-- Wikipedia
Legal Definition
To bind or constrain; to bind to the observance or performance of a duty; to place under an obligation. To bind one's self by an obligation or promise; to assume a duty; to execute a written promise or covenant; to make a writing obligatory. Wachter v. Famachon, 62 Wis. 117, 22 N. W. 160; Maxwell v. Jacksonville Loan & Imp. Co.., 45 Fla. 425, 34 South. 255.
-- Black's Law Dictionary