If the cell was large it would take a long time to perform the tasks given by the nucleus, since the chemical reactions involved in a cell s function are fairly complicated and do not work well on a larger scale. Smaller cells also have the advantage of a greater surface area for their mass, thus allowing them to communicate with their environment. 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.