buylotrogold

ECO CENTRAL 15            Biological Functions, Ecosystem Functions Hierarchical Levels of Organization The fact that nature has different levels of organization , or discernible structures and phenomena at different scales of time and size, is familiar in physical science as well as in biological science. Quarks and leptons, atomic nuclei, atoms, and molecules form a series of organizational levels, or a hierarchy, each level of which has a characteristic scale and is the domain of some area of science: particle physics, nuclear physics, atomic physics, chemistry. This hierarchy can be continued into the scales at which biological phenomena occur and are studied by their corresponding sciences: proteins and other biological molecules (biochemistry), organelles and  cells (biochemistry and cell biology), tissues, organs, and organ systems (physiology, anatomy), organisms (autecology), populations (population biology), communities (community ecology), ecosystems (ecosystem ecology), the biosphere (biogeography and global ecology). The time scales associated with these levels generally increase from the extremely short time scales of the strong interactions at the lowest level mentioned above (quarks), up to the hundred million year time scales of some of the biosphere's biogeochemical cycles, e.g. the phosphorous cycle. The distance scales also increase, from somewhat less than the diameter of a proton up to something like the diameter of the earth. Biological Functions and Evolution Each level of the hierarchy has properties which can be explained by reference to the properties of the levels *below* it, a type of explanation called *reductive explanation*. In the living part of the hierarchy, some of the properties of a level also require reference to the level *above* it in order to be understood: these properties are *functions* without which the organization at the level above could not be maintained, e.g. the functions performed by an organ which are required by an organism to stay alive. This is quite different from what is the case in the nonliving part of the hierarchy: atoms do not perform functions for molecules, nor electrons for atoms. Everything that an electron or atom does can be understood without reference to molecules. But the functions of the liver, e.g., cannot be understood without reference to the rest of the organism and its life requirements. Although the functions of the liver are a *result* of the properties of its lower-level structure (that is, reductive explanation applies), understanding what the liver *does*