This simple cartoon shows general similarities and differences between eukaryote and prokaryote cells. Click on image for full size (24K GIF) Modified from NIH

The Cell Theory states that all living things are made of cells, which are the basic units of life, and that cells come from other cells.

Prokaryotic cells have no nucleus or organelles enclosed within membranes. Species in the domains Archaea and Eubacteria have prokaryotic cells.

Eukaryotic cells have a nucleus and organelles that are surrounded by membranes. Each organelle does a specific cell function. All species in the Eukaryota domain (protists, fungi, plants, and animals) have eukaryotic cells. Individual protists have only one cell, while plants and animals can have trillions of cells. Complex creatures like humans have special cells for special functions like carrying oxygen around the body, digesting food, or making bone.