What are the processes by which substances can enter or leave the cell without ever passing through the cell membrane?
Substances can enter a cell without ever passing through the cell membrane through the process of endocytosis. The two types of endocytosis include phagocytosis, or the invagination of large particles via the flow of the cell membrane around the particle, and pinocytosis, or the invagination of small particles via the formation of narrow channels in the cell membrane directly beneath the particle after the particle has bound to the surface of the membrane. Following either type of endocytosis, the vesicles containing the particles become detached from the cell membrane and migrate toward the interior of the cell. Eventually, the vesicle membrane must disintegrate for the particle to truly enter the cell. In exocytosis, the process of endocytosis is reversed, and vesicles expel substances, often secretory substances (such as hormones) or wastes, after moving from the cell's interior to the cell membrane.
