noun, plural: organisms
An organism refers to any individual living thing that can react to stimuli, reproduce, grow, and maintain homeostasis. It can be a virus, bacterium, protist, fungus, plant or an animal. The earth is home to various organisms and these organisms can be classified taxonomically. There are eight major taxonomic levels: [domain]], kingdom, phyla, class, order, [family]], genus, and species. The three-domain system of biological classification as proposed by Carl Woese and others (in 1977) classifies organisms into the following domains: archaea (archaeabacteria), bacteria (eubacteria), and eucarya (eukaryotes). Both domains archaea and bacteria are prokaryotes.
Organisms may also be grouped based on their cellular composition. A single-celled organism is one that consists of only one cell. In contrast, a multicellular organism is one that is comprised of more than one cell and whose cells are organized into tissues, organs, and then into systems.
Word origin: Greek organon ("instrument")
- life form
- living thing
- living being