The World Around Us

Bacterial flagellum in section. The flagellum comprises some 30 structural parts and is frequently cited as a classic example of irreducible complexity.

A section through a bacterial flagellum. Shaped like a hollow tube, 20 nanometres wide, it contains a rotary engine driven by proton-motor force. This drives the filament at speeds of about 1000 rpm and moves liquids among cells. The flagellum comprises some 30 interdependent structural parts.

Credit: Ruiz Villarreal