User:Lexor/Temp/Cell (biology)
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This is a merge-in-progress of material from cell (biology) and the User:Lexor/Temp/Cell (NCBI) article from NCBI's Science Primer.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Epithelial-cells.jpg/160px-Epithelial-cells.jpg)
The cell is the structural and functional unit of all living organisms. Some organisms, such as bacteria, are unicellular, consisting of a single cell. Other organisms, such as humans, are multicellular, (humans have an estimated 100,000 billion cells). The cell theory, first developed in the 19th century, states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells and that cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.