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. These cellular structures are known as organelles and allow the cell to function properly within its specified environment. The structures of an animal cell are the nucleus, endoplasmic reticulum (rough and smooth), Golgi apparatus, mitochondria, lysosomes, ribosomes, and centrioles. The plant cell has all of the above and the addition of a cell wall, and chloroplasts which aid photosynthesis.
Other uses 
Ultra-Structure is also the name given to a notational system for representing complex rules.
- Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz (December 2006). "Evaluating Support for the Current Classification of Eukaryotic Diversity". PLoS Genet. 2 (12): e220. doi:10.1371/journal.pgen.0020220. PMC 1713255. PMID 17194223.
- 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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