SignificanceIn contemporary life, a molecule’s permeability across cell membranes is tightly regulated by protein transporters. How did primitive cells obtain nutrients, prior to the advent of such transporters? Molecules can passively diffuse across membranes, but importing nutrients in this manner would require a primitive cell to reside in a pool of nutrients for hours if not days. If the membrane is too permeable, nutrients would leak out as soon as they enter. Worse still, leaky membranes would lose primordial genetic material. We present a physicochemical method for triggering passive endocytosis in model primitive cells. The import of nutrients into a stable internalized compartment enables the model primitive cell to gradually absorb the nutrients, thereby breaking the symmetry of passive permeation.