In biology
and ecology,
an organism is a
living being.
The origin 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
prokaryotes and eukaryotes is widely considered a major missing link in
evolutionary history. Two eukaryotic
organelles,
namely
mitochondria and
chloroplasts, are generally considered to be derived from
endosymbiotic bacteria.
The phrase complex organism describes any organism with more than
one cell.
Characteristics common to many organisms include:
These are not universal, however. Many organisms are incapable of
independent movement, and do not respond directly to their environment.
microorganisms such as bacteria may not conduct respiration, using
alternate chemical pathways instead. And many organisms are incapable of
reproduction.
Biological Organization
Environmental Organization
Classification
The following articles are entry points for information about the
classification of organisms:
Viruses
Viruses are
not typically considered to be organisms because they are not capable of
independent
reproduction or
metabolism. This is problematic, though, since some
parasites
and
endosymbionts are incapable of independent life either. Although viruses
do have enzymes
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 hosts.
Life span
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.
External links
-
NCBI Taxonomy entry: root ()
-
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 Tree of Life (http://tolweb.org/tree/phylogeny.html).
-
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...."
-
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
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
-
Jacob Feldman: Stramenopila
-
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.
See also
