bioluminescence, production of light by living organisms. Organisms that are bioluminescent include certain fungi and bacteria that emit light continuously. The dinoflagellates, a group of marine algae, produce light only when disturbed. Bioluminescent animals include such organisms as ctenophores, annelid worms, mollusks, insects such as fireflies, and fish. The production of light in bioluminescent organisms results from the conversion of chemical energy to light energy. In fireflies, one type of a group of substances known collectively as luciferin combines with oxygen to form an oxyluciferin in an excited state, which quickly decays, emitting light as it does. The reaction is mediated by an enzyme, luciferase, which is normally bound to ATP (see adenosine triphosphate) in an inactive form. When the signal for the specialized bioluminescent cells to flash is receive, the luciferase is liberated from the ATP, causes the luciferin to oxidize, and then somehow recombines with ATP. Different organisms produce different bioluminescent substances. Bioluminescent fish are common in ocean depths; the light probably aids in species recognition in the darkness. Other animals seem to use luminescence in courtship and mating and to divert predators or attract prey.

Emission of light by an organism or biochemical system (e.g., the glow of bacteria on decaying meat or fish, the phosphorescence of protozoans in tropical seas, the flickering signals of fireflies). It occurs in a wide range of protists and animals, including bacteria and fungi, insects, marine invertebrates, and fish. It is not known to exist naturally in true plants or in amphibians, reptiles, birds, or mammals. It results from a chemical reaction that produces radiant energy very efficiently, giving off very little heat. The essential light-emitting components are usually the organic molecule luciferin and the enzyme luciferase, which are specific for different organisms. In higher organisms, light production is used to frighten predators and to help members of a species recognize each other. Its functional role in lower organisms such as bacteria, dinoflagellates, and fungi is uncertain. Luminous species are widely scattered taxonomically, with no clear-cut pattern, though most are marine.

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