Cellular movements caused by the actions of flagella and cilia

Both flagella and cilia cause movement by a bending motion. In flagella, movement occurs by a whiplike motion that is due to the propagation of a bend from the base to the tip. In addition, the nature of swimming depends on the length of the appendage and whether it involves coordination among multiple flagella or cilia. (a) Sperm swim by means of a single, long flagellum that moves in a whiplike motion. (b) The swimming of Chlamydomonas reinhardtii also involves a whiplike motion at the base, but the motion is precisely coordinated between two flagella. This results in swimming behaviour that resembles a breaststroke. (c) Ciliated protozoa swim via many shorter cilia. The bending motion is coordinated among multiple adjacent cilia. All three images are light micrographs; (a) and (c) are colorized.