Eukaryotic and Prokaryotic Cells
Prokaryotic cells, such as bacteria, have a free-floating chromosome that is usually circular and is not enclosed in a nuclear membrane. Instead, the DNA simply exists in a region of the cell called the nucleoid. Prokaryotic cells only have a small range of organelles, generally only a plasma membrane and ribosomes. Eukaryotic cells, on the other hand, have chromosomes that are enclosed in a true nucleus, and are therefore separated from the cytoplasm by the nuclear membrane. Eukaryotic cells also have a wide range of organelles that perform specialized functions.
Sources: image from the NCBI Science Primer: What is a Cell?