EXPERIMENTAL FIGURE 18-32 Video microscopy shows flagellar movements that propel sperm and Chlamydomonas forward. In both cases, the cells are moving to the left. (a) In the typical sperm flagellum, successive waves of bending originate at the base and are propagated out toward the tip; these waves push against the surrounding fluid and propel the cell forward. Captured in this multiple-exposure sequence, a bend at the base of the flagellum in the first (top) frame has moved distally halfway along the flagellum by the last frame. A pair of gold beads attached to the flagellum are seen to slide apart as the bend moves through their region. (b) Beating of the two flagella on Chlamydomonas occurs in two stages, called the effective stroke (top three frames) and the recovery stroke (remaining frames). The effective stroke pulls the organism through the water. During the recovery stroke, a different wave of bending moves outward from the bases of the flagella, pushing the flagella along the surface of the cell until they reach the position to initiate another effective stroke. Beating commonly occurs 5–10 times per second.