Organism

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The term "organism" (Greek ὀργανισμός - organismos, from Ancient Greek ὄργανον - organon "organ, instrument, tool") first appeared in the English language in 1701 and took on its current definition by 1834 (Oxford English Dictionary).

Chambers Online Reference provides a broad definition: "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction".

Quote

There is original endowment of adaptation in living things and beings. In every living plant or animal cell, in every living organism--material or spiritual--there is an insatiable craving for the attainment of ever-increasing perfection of environmental adjustment, organismal adaptation, and augmented life realization. These interminable efforts of all living things evidence the existence within them of an innate striving for perfection.

Biologic

In biology, an organism is any living thing (such as animal, plant, fungus, or micro-organism). In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many billions of cells grouped into specialized tissues and organs. The term multicellular (many-celled) describes any organism made up of more than one cell.

Organisms may be divided into the prokaryotic and eukaryotic groups. The prokaryotes represent two separate domains, the Bacteria and Archaea. 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. Viruses are dependent on the biochemical machinery of a host cell for reproduction.

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.

Viruses

Viruses are not typically considered to be organisms because they are incapable of "independent" reproduction or metabolism. This controversy is problematic, though, since some parasites and endosymbionts are also incapable of independent life. Although viruses have a few enzymes and molecules characteristic of living organisms, they are incapable of reproducing outside a host cell and most of their metabolic processes require a host and its 'genetic machinery' such as organelles in eukaryotic hosts and the assemblage of ready-made enzymes (which the virus cannot make by itself) in prokaryotic hosts. While viruses sustain no independent metabolism, and thus are usually not accounted organisms, they do have their own genes and they do evolve by the same mechanisms by which organisms evolve.

Superorganism

A superorganism is an organism consisting of many individuals working together as a single functional or social unit. Ants, and other eusocial invertebrates such as termites, are examples of superorganisms that form large colonies of individuals with highly specialised roles and division of labor. Individuals may be unable to reproduce or to survive for extended periods of time when separated from the colony. By working cooperatively, superorganisms can achieve feats that comparable solitary organisms cannot. Thermoregulation, for example, does not occur in individuals or small groups of honeybees or other invertebrates, but colonies of bees with more than about 5000 individuals can thermoregulate.[1]

James Lovelock, with his "Gaia Theory" has paralleled the work of Vladimir Vernadsky, who suggested the whole of the biosphere in some respects can be considered as a superorganism.

The concept of superorganism is under dispute, as many biologists maintain that in order for a social unit to be considered an organism by itself, the individuals should be in permanent physical connection to each other, and its evolution should be governed by selection to the whole society instead of individuals. While it's generally accepted that the society of eusocial animals is a unit of natural selection to at least some extent, most evolutionists claim that the individuals are still the primary units of selection.

The question remains "What is to be considered the individual?". Advocates of evolution like Richard Dawkins suggest that the individual selected is the "Selfish Gene". Others believe it is the whole genome of an organism. E.O. Wilson has shown that with ant-colonies and other social insects it is the breeding entity of the colony that is selected, and not its individual members. This could apply to the bacterial members of a stromatolite, which, because of genetic sharing, in some way comprise a single gene pool. Gaian theorists like Lynn Margulis would argue this applies equally to the symbiogenesis of the bacterial underpinnings of the whole of the Earth.

It would appear, from computer simulations like Daisyworld that biological selection occurs at multiple levels simultaneously.

It is also argued that humans are actually a superorganism that includes microorganisms such as bacteria. It is estimated that "the human intestinal microbiota is composed of 10x13th to 10x14th microorganisms whose collective genome ("microbiome") contains at least 100 times as many genes as our own[...] Our microbiome has significantly enriched metabolism of glycans, amino acids, and xenobiotics; methanogenesis; and 2-methyl-D-erythritol 4-phosphate pathway–mediated biosynthesis of vitamins and isoprenoids. Thus, humans are superorganisms whose metabolism represents an amalgamation of microbial and human attributes." [2]. An NIH-coordinated and -funded effort is currently in progress to characterize the human microbiome.[3]

See also

References

  1. T.Cavalier-Smith (1987) The origin of eukaryote and archaebacterial cells, Annals of the New York Academy of Sciences 503, 17–54
  2. "organism". Oxford English Dictionary (online ed.). 2004.
  3. "organism". Chambers 21st Century Dictionary (online ed.). 1999.
  4. Southwick, Edward E. (1983). "The honey bee cluster as a homeothermic superorganism" (PDF). Comparative Biochemistry and Physiology 75A (4): 741–745. doi:10.1016/0300-9629(83)90434-6. http://www.sciencedirect.com/science?_ob=MiamiImageURL&_imagekey=B6T2P-4867WXH-110-2&_cdi=4924&_user=4385511&_check=y&_orig=search&_coverDate=12%2F31%2F1983&_qd=1&view=c&wchp=dGLbVlz-zSkWW&md5=d23bd1cec870de7f5a44f8a2f367ed9c&ie=/sdarticle.pdf. Retrieved on 2006-07-20.
  5. Gill S. R., et al. Science, 312, 1355-1359 (2006). http://dx.doi.org/10.1126/science.1124234
  6. The Universal Features of Cells on Earth in Chapter 1 of Molecular Biology of the Cell fourth edition, edited by Bruce Alberts (2002) published by Garland Science.
  7. Doolittle, W. Ford (February, 2000). Uprooting the tree of life. Scientific American 282 (6): 90–95.
  8. NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
  9. Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
  10. NCBI: "The Genetic Codes", Compiled by Andrzej (Anjay) Elzanowski and Jim Ostell
  11. Jukes TH, Osawa S, The genetic code in mitochondria and chloroplasts., Experientia. 1990 Dec 1;46(11-12):1117-26.
  12. Genetic Code page in the NCBI Taxonomy section (Downloaded 27 April 2007.)
  13. Syoso Osawa (1995). Evolution of the Genetic Code. Oxford University Press. pp. 232. ISBN 978-0198547815.
  14. Evaluation of the Rate of Evolution in Natural Populations of Guppies (Poecilia reticulata) "[1]"
  15. Oklahoma State - Horizontal Gene Transfer
  16. esalenctr.org
  17. Gibsona, Daniel G., Gwynedd A. Benders, Kevin C. Axelroda, Jayshree Zaveria, Mikkel A. Algirea, Monzia Moodiea, Michael G. Montaguea, J. Craig Ventera, Hamilton O. Smith, and Clyde A. Hutchison III (2008). "One-step assembly in yeast of 25 overlapping DNA fragments to form a complete synthetic Mycoplasma genitalium genome". PNAS 105 (51): 20404-20409. http://www.pnas.org/content/105/51/20404.full.pdf.

External links