In biology, an organism is an individual living system (such as animal, plant, fungus, or micro-organism). In at least some form, all organisms are capable of reacting to stimuli, reproduction, growth and maintenance as a stable whole (after FAO[1]). An organism may be unicellular or made up, as in humans, of many billions of cells grouped into specialized tissues and organs. The phrase complex organism describes any organism with more than one cell.
The term "organism" (Greek οργανισμός - organismos, from Ancient Greek όργανον - organon, "organ, instrument, tool") first appeared in the English language in 1701 and took on its current definition by 1834 (Oxford English Dictionary).
Organisms may be divided into the prokaryotic and eukaryotic groups. The prokaryotes represent two separate domains, the Bacteria and Archaea.[2] All fungi, animals and plants are eukaryotes.
The word "organism" may broadly be defined as an assembly of molecules that function as a more or less stable whole and has the properties of life. However, many sources propose definitions that exclude viruses and theoretically-possible man-made non-organic life forms.[3] Viruses are dependent on the biochemical machinery of a host cell for reproduction.
Chambers Online Reference provides a broad definition: "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction"[4].
In multicellular life the word "organism" usually describes the whole hierarchical assemblage of systems (for example circulatory, digestive, or reproductive) themselves collections of organs; these are, in turn, collections of tissues, which are themselves made of cells. In some plants and the nematode Caenorhabditis elegans, individual cells are totipotent.
Remember class to read pages 113-136 and study the virus section of the quiz questions in the back. They will be on the test friday.
