Every such opening is an exception to the rule of integrity; after all, a doorway to the outside is also a doorway to the inside. Viruses or other microbes might use the routes of nutrient uptake or waste disposal to enter a cell. Porosity, in short, represents an essential feature of life—but also an essential vulnerability of living. A perfectly sealed cell is a perfectly dead cell. But unsealing the membrane through portals exposes the cell to potential harm. The cell must embrace both: closed to the outside, yet open to the outside.
