Bacteria are small and simple in structure when compared with eucaryotes, yet they often have characteristic shapes and sizes.

Although they have a plasma membrane, which is required by all living cells, bacteria generally lack extensive, complex, internal membrane systems.

The cytoplasmic matrix typically contains several constituents that are not membrane-enclosed: inclusion bodies, ribosomes, and the nucleoid with its genetic material.

The procaryotic cell wall almost always has peptidoglycan and is chemically and morphologically complex.

Most bacteria can be divided into gram-positive and gram-negative groups based on their cell wall structure and response to the Gram stain.

Components like capsules and fimbriae are located outside the cell wall. One of these is the flagellum which many bacteria use like a propeller to swim toward attractants and away from repellents.

Some bacteria form resistant endospores to survive harsh environmental conditions in a dormant state.