<P> 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 inseciticidal 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 . </P> <P> The simple standard biological organization scheme, from the lowest level to the highest level, is as follows: </P> <Table> <Tr> <Td_colspan="3"> For levels smaller than atoms see Subatomic particle </Td> </Tr> <Tr> <Td> Acellular level and Pre-cellular level </Td> <Td> Atoms </Td> <Td> </Td> </Tr> <Tr> <Td> Molecule </Td> <Td> Groups of atoms </Td> </Tr> <Tr> <Td> Biomolecular complex </Td> <Td> Groups of (bio) molecules </Td> </Tr> <Tr> <Td> Sub-cellular level </Td> <Td> Organelle </Td> <Td> Functional groups of biomolecules, biochemical reactions and interactions </Td> </Tr> <Tr> <Td> Cellular level </Td> <Td> Cell </Td> <Td> Basic unit of all life and the grouping of organelles </Td> </Tr> <Tr> <Td> Super-cellular level (Multicellular level) </Td> <Td> Tissue </Td> <Td> Functional groups of cells </Td> </Tr> <Tr> <Td> </Td> <Td> Organ </Td> <Td> Functional groups of tissues </Td> </Tr> <Tr> <Td> Organ system </Td> <Td> Functional groups of organs </Td> </Tr> <Tr> <Td> Ecological levels </Td> <Td> Organism </Td> <Td> The basic living system, a functional grouping of the lower - level components, including at least one cell </Td> </Tr> <Tr> <Td> Population </Td> <Td> Groups of organisms of the same species </Td> </Tr> <Tr> <Td> Community (or biocoenosis) </Td> <Td> Interspecific groups of interacting populations </Td> </Tr> <Tr> <Td> Ecosystem </Td> <Td> Groups of organisms from all biological domains in conjunction with the physical (abiotic) environment </Td> </Tr> <Tr> <Td> Biome </Td> <Td> Continental scale (climatically and geographically contiguous areas with similar climatic conditions) grouping of ecosystems . </Td> </Tr> <Tr> <Td> Biosphere or Ecosphere </Td> <Td> All life on Earth or all life plus the physical (abiotic) environment </Td> </Tr> <Tr> <Td_colspan="3"> For levels larger than Biosphere or Ecosphere, see Earth's location in the Universe </Td> </Tr> </Table> <Tr> <Td_colspan="3"> For levels smaller than atoms see Subatomic particle </Td> </Tr>

Levels of biological hierarchy from smallest to largest
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