Biological organization is the organization ofcomplexbiologicalstructures andsystems that definelife using areductionistic approach.[1] The traditional hierarchy, as detailed below, extends fromatoms tobiospheres. The higher levels of this scheme are often referred to as anecological organizational concept, or as thefield,hierarchical ecology.
Each level in the hierarchy represents an increase in organizationalcomplexity, with each "object" being primarily composed of the previous level's basic unit.[2] The basic principle behind the organization is the concept ofemergence—the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels.[3]
The biological organization of life is a fundamental premise for numerous areas ofscientificresearch, particularly in themedical sciences. Without this necessary degree of organization, it would be much more difficult—and likely impossible—to apply the study of the effects of variousphysical andchemical phenomena todiseases andphysiology (body function). For example, fields such ascognitive andbehavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts ofpharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into theecological levels as well. For example,DDT's directinsecticidal effect occurs at thesubcellular level, but affects higher levels up to and including multipleecosystems. Theoretically, a change in oneatom could change the entirebiosphere.
The simple standard biological organization scheme, from the lowest level to the highest level, is as follows:[1]
| For levels smaller than atoms seeSubatomic particle | ||
| Acellular level and Pre-cellular level | Atoms | |
| Molecule | Groups of atoms | |
| Biomolecular complex | Groups of (bio)molecules | |
| Sub-cellular level | Organelle | Functional groups of biomolecules, biochemical reactions and interactions |
| Cellular level | Cell | Basic unit of all life and the grouping of organelles |
| Super-cellular level (Multicellular level) | Tissue | Functional groups of cells |
| Organ | Functional groups of tissues | |
| Organ system | Functional groups of organs | |
| Ecological levels | Organism | The basic living system, a functional grouping of the lower-level components, including at least one cell |
| Population | Groups of organisms of the samespecies | |
| Guild | Interspecific groups of organisms carrying the same ecological function (i.e.herbivores). | |
| Community (orbiocoenosis) | Guilds from all biologicaldomains, and their interactions in a specific location. | |
| Ecosystem | Groups of organisms in conjunction with the physical (abiotic) environment. | |
| Biome | Continental 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[4] | |
| For levels larger than Biosphere or Ecosphere, seeEarth's location in the Universe | ||
More complex schemes incorporate many more levels. For example, a molecule can be viewed as a grouping ofelements, and an atom can be further divided intosubatomic 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 ofgenes.[5]
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 asemergent properties.
Every organism is organized, though not necessarily to the same degree.[6] An organism can not be organized at thehistological (tissue) level if it is not composed of tissues in the first place.[7]
Biological organization is thought to have emerged in the earlyRNA world whenRNA chains began to express the basic conditions necessary for natural selection to operate as conceived byDarwin (heritability, variation of type, and competition for limited resources).Fitness of an RNA replicator (its per capita rate of increase) would likely have been a function of adaptive capacities that were intrinsic (in the sense that they were determined by the nucleotide sequence) and the availability of resources.[8][9] The three primary adaptive capacities may have been:
(1) the capacity to replicate with moderate fidelity (giving rise to both heritability and variation of type).
(2) the capacity to avoid decay.
(3) the capacity to acquire and process resources.[8][9]
These capacities would have been determined initially by the folded configurations of the RNA replicators (see "Ribozyme") that, in turn, would be encoded in their individual nucleotide sequences. Competitive success among different RNA replicators would have depended on the relative values of these adaptive capacities. Subsequently, among more recent organisms competitive success at successive levels of biological organization, presumably continued to depend, in a broad sense, on the relative values of these adaptive capacities.
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,[10][11] laid the empirical foundations for afield that would be, from the 1980s,hierarchical ecology.[12][13][14][15][16]
The theoretical foundations are summarized by thermodynamics. Whenbiological systems are modeled asphysical systems, in its most general abstraction, they arethermodynamic open systems that exhibitself-organized behavior,[17] and theset/subset relations betweendissipative 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 inEcology byOdum and others as the "Simon's hierarchical principle";[18] Simon[19] emphasized that hierarchy "emerges almost inevitably through a wide variety of evolutionary processes, for the simple reason thathierarchical structures are stable".
| 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. |
Cell physiology (inHuman Physiology) at WikibooksCharacteristics of life andthe nature of molecules (inGeneral Biology) at Wikibooksorganization within the biosphere (inEcology) at Wikibooks
