Biological organisation

Biological organization is the hierarchy of complex biological structures and systems that define life using a reductionistic approach.[1] The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as an ecological organization concept, or as the field, hierarchical ecology.

"Hierarchy of life" and "Levels of organization" redirect here. For the hierarchical ordering and organization of all organisms, see Biological classification. For the evolutionary hierarchy of organisms and interspecial relationships, see Phylogenetic tree.

Each level in the hierarchy represents an increase in organizational complexity, with each "object" being primarily composed of the previous level's basic unit.[2] The basic principle behind the organization is the concept of emergence—the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels.

The biological organization of life is a fundamental premise for numerous areas of scientific research, particularly in the medical sciences. Without this necessary degree of organization, it would be much more difficult—and likely impossible—to apply the study of the effects of various physical and chemical phenomena to diseases and physiology (body function). For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into the ecological levels as well. For example, DDT's direct insecticidal effect occurs at the subcellular level, but affects higher levels up to and including multiple ecosystems. Theoretically, a change in one atom could change the entire biosphere.

Levels
See also: Integrative level
The simplest unit of life is the atom, like oxygen. Two or more atoms is a molecule, like a dioxide. Many small molecules may combine in a chemical reaction to make up a macromolecule, such as a phospholipid. Multiple macromolecules form a cell, like a club cell. A group of cells functioning together as a tissue, for example, Epithelial tissue. Different tissues make up an organ, like a lung. Organs work together to form an organ system, such as the Respiratory System. All of the organ systems make a living organism, like a lion. A group of the same organism living together in an area is a population, such as a pride of lions. Two or more populations interacting with each other form a community, for example, lion and zebra populations interacting with each other. Communities interacting not only with each other but also with the physical environment encompass an ecosystem, such as the Savanna ecosystem. All of the ecosystems make up the biosphere, the area of life on Earth.

The simple standard biological organization scheme, from the lowest level to the highest level, is as follows:[1]

For levels smaller than atoms see Subatomic particle
Acellular level
and
Pre-cellular level		Atoms
MoleculeGroups of atoms
Biomolecular complexGroups of (bio)molecules
Sub-cellular levelOrganelleFunctional groups of biomolecules, biochemical reactions and interactions
Cellular levelCellBasic unit of all life and the grouping of organelles
Super-cellular level
(Multicellular level)		TissueFunctional groups of cells
OrganFunctional groups of tissues
Organ systemFunctional groups of organs
Ecological levelsOrganismThe basic living system, a functional grouping of the lower-level components, including at least one cell
PopulationGroups of organisms of the same species
Community
(or biocoenosis)		Interspecific groups of interacting populations
EcosystemGroups of organisms from all biological domains in conjunction with the physical (abiotic) environment
BiomeContinental scale (climatically and geographically contiguous areas with similar climatic conditions) grouping of ecosystems.
Biosphere or
Ecosphere		All life on Earth or all life plus the physical (abiotic) environment[3]
For levels larger than Biosphere or Ecosphere, see Earth's location in the Universe

More complex schemes incorporate many more levels. For example, a molecule can be viewed as a grouping of elements, and an atom can be further divided into subatomic particles (these levels are outside the scope of biological organization). Each level can also be broken down into its own hierarchy, and specific types of these biological objects can have their own hierarchical scheme. For example, genomes can be further subdivided into a hierarchy of genes.[4]

Each level in the hierarchy can be described by its lower levels. For example, the organism may be described at any of its component levels, including the atomic, molecular, cellular, histological (tissue), organ and organ system levels. Furthermore, at every level of the hierarchy, new functions necessary for the control of life appear. These new roles are not functions that the lower level components are capable of and are thus referred to as emergent properties.

Every organism is organised, though not necessarily to the same degree.[5] An organism can not be organised at the histological (tissue) level if it is not composed of tissues in the first place.[6]

Fundamentals

Empirically, a large proportion of the (complex) biological systems we observe in nature exhibit hierarchical structure. On theoretical grounds we could expect complex systems to be hierarchies in a world in which complexity had to evolve from simplicity. System hierarchies analysis performed in the 1950s,[7][8] laid the empirical foundations for a field that would be, from the 1980s, hierarchical ecology.[9][10][11][12][13]

The theoretical foundations are summarized by thermodynamics. When biological systems are modeled as physical systems, in its most general abstraction, they are thermodynamic open systems that exhibit self-organised behavior, and the set/subset relations between dissipative structures can be characterized in a hierarchy.

A simpler and more direct way to explain the fundamentals of the "hierarchical organization of life", was introduced in Ecology by Odum and others as the "Simon's hierarchical principle";[14] Simon[15] emphasized that hierarchy "emerges almost inevitably through a wide variety of evolutionary processes, for the simple reason that hierarchical structures are stable".

To motivate this deep idea, he offered his "parable" about imaginary watchmakers.

Parable of the Watchmakers

There once were two watchmakers, named Hora and Tempus, who made very fine watches. The phones in their workshops rang frequently; new customers were constantly calling them. However, Hora prospered while Tempus became poorer and poorer. In the end, Tempus lost his shop. What was the reason behind this?

The watches consisted of about 1000 parts each. The watches that Tempus made were designed such that, when he had to put down a partly assembled watch (for instance, to answer the phone), it immediately fell into pieces and had to be reassembled from the basic elements.

Hora had designed his watches so that he could put together subassemblies of about ten components each. Ten of these subassemblies could be put together to make a larger sub-assembly. Finally, ten of the larger subassemblies constituted the whole watch. Each subassembly could be put down without falling apart.

See also

Notes
  1. Solomon, Berg & Martin 2002, pp. 9–10
  2. Pavé 2006, p. 40
  3. Huggett 1999
  4. Pavé 2006, p. 39
  5. Postlethwait & Hopson 2006, p. 7
  6. Witzany, G (2014). "Biological Self-organization". International Journal of Signs and Semiotic Systems. 3 (2): 1–11.
  7. Evans 1951
  8. Evans 1956
  9. Margalef 1975
  10. O'Neill 1986
  11. Wicken & Ulanowicz 1988
  12. Pumain 2006
  13. Jordan & Jørgensen 2012
  14. Simon 1969, pp. 192–229
  15. Simon's texts at doi:10.1207/S15327809JLS1203_4, polaris.gseis.ucla.edu/pagre/simon Archived July 5, 2015, at the Wayback Machine or johncarlosbaez/2011/08/29 transcriptions Archived 2015-05-31 at the Wayback Machine

References
  • Evans, F. C. (1951), "Ecology and urban areal research", Scientific Monthly (73)
  • Evans, F. C. (1956), "Ecosystem as basic unit in ecology", Science, 123: 1127–8, Bibcode:1956Sci...123.1127E, doi:10.1126/science.123.3208.1127, PMID 17793430
  • Huggett, R. J. (1999). "Ecosphere, biosphere, or Gaia? What to call the global ecosystem. ECOLOGICAL SOUNDING". Global Ecology and Biogeography. 8 (6): 425–431. doi:10.1046/j.1365-2699.1999.00158.x. ISSN 1466-822X.CS1 maint: ref=harv (link)
  • Jordan, F.; Jørgensen, S. E. (2012), Models of the Ecological Hierarchy: From Molecules to the Ecosphere, ISBN 9780444593962
  • Margalef, R. (1975), "External factors and ecosystem stability", Schweizerische Zeitschrift für Hydrologie, 37: 102–117, doi:10.1007/BF02505181
  • O'Neill, R. V. (1986), A Hierarchical Concept of Ecosystems, ISBN 0691084378
  • Pavé, Alain (2006), "Biological and Ecological Systems Hierarchical organization", in Pumain, D. (ed.), Hierarchy in Natural and Social Sciences, New York, New York: Springer-Verlag, ISBN 978-1-4020-4126-6
  • Postlethwait, John H.; Hopson, Janet L. (2006), Modern Biology, Holt, Rinehart and Winston, ISBN 0-03-065178-6
  • Pumain, D. (2006), Hierarchy in Natural and Social Sciences, ISBN 978-1-4020-4127-3
  • Simon, H. A. (1969), "The architecture of complexity", The Sciences of the Artificial, Cambridge, Massachusetts: MIT Press
  • Solomon, Eldra P.; Berg, Linda R.; Martin, Diana W. (2002), Biology (6th ed.), Brooks/Cole, ISBN 0-534-39175-3, LCCN 2001095366
  • Wicken, J. S.; Ulanowicz, R. E. (1988), "On quantifying hierarchical connections in ecology", Journal of Social and Biological Systems, 11: 369–377, doi:10.1016/0140-1750(88)90066-8
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