Organism

An organism is a living being.

The origins of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered to represent two separate domains, called the Bacteria and Archaea, which are not closer to one another than to the eukaryotes. The gap between prokaryote and eukaryotes is widely considered as a major missing link in evolutionary history. Two eukaryotic organelles, namely mitochondria[?] and chloroplasts, are generally considered to be derived from endosymbiotic bacteria.

Characteristic common to many organisms include:

• Movement
• Feeding
• Respiration
• Growth
• Reproduction
• Sensitivity to stimuli

These are not universal, however. Many organisms are incapable of independent movement, and do not respond directly to their environment. Bacteria may not conduct respiration, using alternate chemical pathways instead. And many organisms are incapable of reproduction.

Viruses are not typically considered to be organisms because they are not capable of independent reproduction or metabolism, requiring a host. This is problematic, though, since some extreme parasites or endosymbionts are not capable of independent life. Although viruses do have enzymes and molecules characteristic of living organisms, they are not capable of surviving outside a host cell and most of their metabolic processes require a host and its 'genetic machinery'. The origin such parasites is uncertain, but it appears most likely that they are derived from their hosts.

One of the basic parameters of organism is its life span. Some animals live as short as one day, while other plants can live thousands of years. Aging is important when determining life span of most organisms, bacterium, a virus or even a prion.

See also : Biology microorganism

External links

• NCBI Taxonomy entry: root (http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Root) (rich)
• NCBI Taxonomy resources (http://www.ncbi.nlm.nih.gov/Taxonomy/taxonomyhome/index.cgi?chapter=resources) (rich)
• Species 2000 Indexing the world's known species (http://www.species2000.org/). Species 2000 has the objective of enumerating all known species of plants, animals, fungi and microbes on Earth as the baseline dataset for studies of global biodiversity. It will also provide a simple access point enabling users to link from here to other data systems for all groups of organisms, using direct species-links.
• The Tree of Life (http://tolweb.org/tree/phylogeny). Its basic goals are:
  • to provide a uniform and linked framework in which to publish electronically information about the evolutionary history and characteristics of all groups of organisms
  • to present a modern scientific view of the evolutionary tree that units all organisms on Earth
  • to aid education about and appreciation of biological diversity
  • to provide (eventually) a life-wide data base and searching system about characteristics of organisms
  • to provide a means to find taxon-specific information on the Internet, both taxonomic and otherwise
• Green Plant Phylogeny, Research Coordination Group, "DEEP GREEN", Understanding the Diversity of Plants (http://ucjeps.berkeley.edu/bryolab/GPphylo/). A five-year effort to reconstruct the evolutionary relationships among all green plants has resulted in the most complete "tree of life" of any group of living things on the planet, including animals.
• BBC News, August 4, 1999: The mother of all plants (http://news.bbc.co.uk/1/hi/sci/tech/411757.stm). Scientists have discovered that every plant species alive on land today shares a single common ancestor, at least 450 million years old.
• 7 August, 2000, Fantastic fungus find (http://news.bbc.co.uk/1/hi/sci/tech/869808.stm) Citat: "...Researchers in the US have found what is probably the largest living organism on Earth....Scientists say it covers 890 hectares (2,200 acres) of land - an area equivalent to about 1,220 football pitches. The fungus is called Armillaria ostoyae, but is more popularly known as the honey mushroom. This particular specimen is calculated to be about 2,400 years old, although it could be two to three times this age...."
• BBCNews: 27 September, 2000, When slime is not so thick (http://news.bbc.co.uk/1/hi/sci/tech/944790.stm) Citat: "...It means that some of the lowliest creatures in the plant and animal kingdoms, such as slime and amoeba, may not be as primitive as once thought...."
• BBCNews, 4 December, 2002, Life 'began on the ocean floor' (http://news.bbc.co.uk/1/hi/sci/tech/2541393.stm)
  • SpaceRef.com, July 29, 1997: Scientists Discover Methane Ice Worms On Gulf Of Mexico Sea Floor (http://www.spaceref.com/news/viewpr?pid=4742)
    • The Eberly College of Science: Methane Ice Worms discovered on Gulf of Mexico Sea Floor (http://www.science.psu.edu/iceworms/iceworms) download Publication quality photos
  • Artikel, 2000: Methane Ice Worms: Hesiocaeca methanicola. Colonizing Fossil Fuel Reserves (http://www.sb-roscoff.fr/Ecophy/PDF/00-Fisher-NatWis.pdf)
  • SpaceRef.com, May 04, 2001: Redefining "Life as We Know it" (http://www.spaceref.com/news/viewnews?id=339) Hesiocaeca methanicola In 1997, Charles Fisher, professor of biology at Penn State, discovered this remarkable creature living on mounds of methane ice under half a mile of ocean on the floor of the Gulf of Mexico.
• BBCNews, 18 December, 2002, 'Space bugs' grown in lab (http://news.bbc.co.uk/1/hi/sci/tech/2585235.stm) Citat: "...Bacillus simplex and Staphylococcus pasteuri...Engyodontium album...The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space...."
• BBCNews, 19 June, 2003, Ancient organism challenges cell evolution (http://news.bbc.co.uk/1/hi/sci/tech/3003946.stm) Citat: "..."It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both,"..."
• Saint Anselm College: Survey of representatives of the major Kingdoms (http://www.anselm.edu/homepage/jpitocch/genbios/surveybi04) Citat: "...Number of kingdoms has not been resolved...Bacteria present a problem with their diversity...Protista present a problem with their diversity...", Interactive Syllabus for General Biology - BI 04, Saint Anselm College, Summer 2003 (http://www.anselm.edu/homepage/jpitocch/genbios/bi04syllabsu03)
• Jacob Feldman: Stramenopila (http://www.personal.psu.edu/users/j/s/jsf165/Bio110)