Ultrastructure (or ultra-structure) is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be observed by
electron microscopy. It refers in general to the study of cellular structures that are too small to be seen with an optical microscope.
Ultrastructure, along with
molecular phylogeny, has often been a reliable (that is phylogenetic) way of classifying organisms. [cite journal | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255 | title = Evaluating Support for the Current Classification of Eukaryotic Diversity | author = Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz | doi = 10.1371/journal.pgen.0020220 | journal = PLoS Genet. | date = 2006 December | volume = 2 | issue = 12 | pages = e220 | pmid = 17194223 ]
Ultra-Structure is also the name given to a notational system for representing complex rules. [Long, J., and Denning, D., "Ultra-Structure: A design theory for complex systems and processes." In Communications of the ACM (January 1995)]
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