The Origin Of Life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the Prokaryote s and Eukaryote s. 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 prokaryotes and eukaryotes is widely considered a major missing link in evolutionary history. Two Eukaryotic Organelle s, namely Mitochondria and Chloroplast s, are generally considered to be derived from Endosymbiotic bacteria.
The phrase ''complex organism'' describes any organism with more than one Cell .
Viruses are not typically considered to be organisms because they are not capable of ''independent'' Reproduction or Metabolism . However, according to the United States Code , they are considered to be microorganisms in the sense of biological weaponry and malicious use. This controversy is problematic, though, since some Parasite s and Endosymbiont s are incapable of independent life either. Although viruses do have Enzyme s and molecules characteristic of living organisms, they are incapable of surviving outside a Host Cell and most of their metabolic processes require a host and its 'genetic machinery'. The origin of such parasites is uncertain, but it appears most likely that they are derived from their host.
One of the basic parameters of organism is its Life Span . Some animals live as short as one day, while some plants can live thousands of years. Aging is important when determining life span of most organisms, bacterium, a virus or even a Prion .
- BBCNews: 27 September, 2000, When slime is not so thick 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...."
- --- SpaceRef.com, July 29, 1997: Scientists Discover Methane Ice Worms On Gulf Of Mexico Sea Floor
-- The Eberly College of Science: Methane Ice Worms discovered on Gulf of Mexico Sea Floor download Publication quality photos
- --- Artikel, 2000: Methane Ice Worms: Hesiocaeca methanicola. Colonizing Fossil Fuel Reserves
- --- SpaceRef.com, May 04, 2001: Redefining "Life as We Know it" ''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 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 Citat: "..."It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both,"..."
- Interactive Syllabus for General Biology - BI 04, Saint Anselm College, Summer 2003
- Jacob Feldman: Stramenopila
- NCBI Taxonomy entry: root (rich)
- Saint Anselm College: Survey of representatives of the major Kingdoms Citat: "...Number of Kingdom s has not been resolved...Bacteria present a problem with their diversity... Protista present a problem with their diversity...",
- Species 2000 Indexing the world's known species . 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 largest organism in the world may be a fungus carpeting nearly 10 square kilometers of an Oregon forest, and may be as old as 8500 years.
- The Tree of Life .
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