2.9 Mechanisms of Transport

Cells have membranes that allow them to establish and maintain internal environments that are different from their external environments. Describe the processes that allow ions and other molecules to move across membranes. A variety of processes allow for the movement of ions and other molecules across membranes, including passive and active transport, endocytosis, and exocytosis.

exocytosis

cells secrete molecules via fusion of vesicles with the plasma membrane

endocytosis

cells take in molecules by forming new vesicles from plasma membrane which is pinched inwards

• phagocytosis, pinocytosis, receptor-mediated endocytosis

phagocytosis

type of endocytosis in which the cell engulfs a solid particle and digests it with lysososmes

pinocytosis

type of endocytosis in which the cell gulps droplets of extracellular fluids

receptor-mediated endocytosis

receptors (clathrin protein) coating the vesicle allow cells to gain bulk amounts of substance regardless of concentration

bulk flow

one-way movement of fluids due to pressue (ex. blood flow in vessels)

dialysis

diffusion of solutes across membrane with holes of certain sizes, sorting larger molecules from smaller ones using semipermeable membrane