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The Structure of Cells

Author(s): Center for Educational Outreach


Cells can be classified as either unicellular (bacteria and archaea) or multi-cellular (plants and animals). Different types of cells with different functions can exist within one organism. 

Top image: TEM of a longitudinal thin section of a dividing Escherichia coli bacterium (prokaryote). The centrally located nucleoid is prominent.

Bottom image: TEM showing a central longitudinal section of a unicelluar green alga Chlamydomonas reinhardtii (eukaryote). Internal membranes of different types of organelles can be clearly seen, including a pyrenoid surrounded by starch granules within the cup-shaped chloroplast, Golgi organelles, mitochondria and the nucleus.