Eukaryotic cells are the cells of multicellular organisms such as animals and plants. They have a definite cell structures with a true nucleus, special organelles, particularly membranes and structures. They tend to be approximately 50 times larger than prokaryotics.
A prokaryotic cell are unicellular organism such as bacteria. They are primitive in nature and have no true nucleus with simplistic organelle structures. They tend to be 50x smaller than eukaryotic cells.
Both gram positive and negative bacteria have a cell membrane and a cell wall, however gram negative bacteria also have an outer membrane that makes them almost impenetrable.