Canadian Medical Guide > Organisms Terms and Definitions

Organisms Terms and Definitions:

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	Algae - A major group of polyphyletic organisms of extremely varied morphology and physiology, mostly photosynthetic, but distinguished from plants by their complex form of sexual reproduction. They are freshwater and marine, terrestrial and subterranean; some are neustonic (living at the interface of water and the atmosphere). They live in various protozoa and within other plants. They live also in soil and on soil surfaces, on long-persistent snows, and in Antarctic rocks. Thermophilic algae inhabit hot springs. (From Webster, 3d ed; from Bold & Wynne, Introduction to the Algae, 2d ed, pp1-6)
	Animals - Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain Eukarya.
	Archaea - One of the three domains of life (the others being BACTERIA and Eucarya), formerly called Archaebacteria under the taxon Bacteria, but now considered separate and distinct. They are characterized by: (1) the presence of characteristic tRNAs and ribosomal RNAs; (2) the absence of peptidoglycan cell walls; (3) the presence of ether-linked lipids built from branched-chain subunits; and (4) their occurrence in unusual habitats. While archaea resemble bacteria in morphology and genomic organization, they resemble eukarya in their method of genomic replication. The domain contains at least three kingdoms: CRENARCHAEOTA; EURYARCHAEOTA; and KORARCHAEOTA.
	Bacteria - One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classifed by their response to OXYGEN: aerobic, anerobic, or facultatively anerobic; by the mode by which they obtain their energy: chemotrophic (via chemical reaction) or phototrophic (via light reaction); for chemotrophs by their source of chemical energy: lithotrophic (from inorganic compounds) or organotrophic (from organic compounds); and by where they get their CARBON: heterotrophic (from organic sources) or autotrophic (from CARBON DIOXIDE). They can also be classifed by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.
	Fungi - A kingdom of eukaryotic, heterotrophic organisms that live as saprobes or parasites, including mushrooms, yeasts, smuts, molds, etc. They reproduce either sexually or asexually, and have life cycles that range from simple to complex. Filamentous fungi refer to those that grow as multicelluar colonies (mushrooms and molds).
	Plants - Multicellular, eukaryotic life forms of the kingdom Plantae. They are characterized by a mainly photosynthetic mode of nutrition; essentially unlimited growth at localized regions of cell divisions (MERISTEMS); cellulose within cells providing rigidity; the absence of organs of locomotion; absense of nervous and sensory systems; and an alteration of haploid and diploid generations.
	Viruses - Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells.

Organisms Medical Definitions and Terms

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