Some prokaryotes have a much more complex structure than others. Some contain vesicles or vacuoles, which are closed bag-like sac. Many bacteria can move rapidly by use of their flagella, which is a chain of long threadlike protein molecules connected to the cell. Although these prokaryotes seem very simplistic in structure, they actually can be quite complex. They contain complex molecular systems, use a variety of substances for energy, and in many ways are more versatile in their activities than are the more-complex eukaryotic cells.
Eukaryotes is derived from the roots eu meaning typical, and karyon meaning nucleus.
Although the surface of the cell is covered by a plasma membrane like the prokaryotic cells, they have several other membrane systems that divide the cell into compartments, each with a specialized function. These distinct compartments are called organelles. The plasma membrane that surrounds it has most of the same functions as do the prokaryotic cells, such as transport. The nucleus and cytoplasm are separated by the nuclear envelope. The nuclear envelope is a membrane system consisting of two concentric membranes, one laying on top of the other, with the outer facing the cytoplasm, and the inner facing the nucleoplasm.