chemotaxis is a process by which cells migrate toward higher concentrations of a signaling molecule. the signaling molecule binds cell-surface receptors that result in actin polymerization at the cell membrane. actin polymerization results in the formulation of filamentous actin that exerts a force and leads to protrusion of the leading edge. a researcher tested compound a on chemotaxing cells and measured the relative amount of filamentous actin found in the cells at different times.