Prokaryotic and Eukaryotic Cells

When you picture a cell, it is likely that you picture a eukaryotic (this means true kernel - kernel refers to the nucleus at the center) cell - one with a nucleus. However, this excludes a huge group of cells known as prokaryotic cells. 

Prokaryotic (this means before kernel because this cell evolved first before the nucleus evolved) cells lack a nucleus and most other organelles.