Figure 1.

Phagocytosis of a target particle. Receptors on the cell surface bind ligand molecules on the target, such as a pathogen, dead cell, or bead. As receptors bind more and more ligand molecules, the cell membrane progressively engulfs the target. Upon full engulfment, a phagosome is formed, which fuses with lysosomes, leading to digestion of the target. We denote the arc length of engulfed membrane by a, which gradually increases during engulfment. To see this figure in color, go online.