Mechanisms of flagellar propulsion

Summary

Flagellar propulsion takes place in the viscosity-dominated realm of low Reynolds number fluid dynamics. Volumes of fluid are carried in a capture zone around the moving regions of the flagellum, and the flagellar motion achieves propulsion because some of that water is shed from the capture zone, either from the flagellar tip in typical flagellar motion or to the side reached at the end of the effective stroke in the case of ciliary motion. Helical flagellar motion is in principle more efficient than planar beating, and the rotation caused by the former introduces complications in propulsion that may be advantageous, e.g., in Euglena, or disadvantageous, e.g., in a fixed cell. The presence of a surface near to the moving organelle restricts the fluid motion, but this effect enhances ciliary propulsion. There is a great variety of beat patterns, functionally adapted hydrodynamically or in other ways for locomotion, feeding, and other more restricted roles.