The small size of cells did not allow them to be discovered until 1665, when the first microscope was invented. For the most part there are Prokaryote cells and Eukaryote cells. An easy way to remember the difference is thinking of P standing for prehistoric. Prokaryotes are the more basic of the two kinds of cells. A prokaryote cell is very simple in its structure and function.
Bacteria are prokaryote cells.
These cells have a membrane and a very simple nuclear region. There are not separate divisions in the bacterium that carry on their own chemical reactions. For the most part, in a bacteria cell, what you see is what you get. The Eukaryote cell is the more advanced of the two, and most cells are eukaryotic in nature. The structure of these cells is much more complicated and diverse than the structure of prokaryotic cells.