Vesicle (biology and chemistry) - Wikipedia Scheme of a liposome formed by phospholipids in an aqueous solution [further explanation needed] In cell biology, a vesicle is an organelle within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis), and the transport of materials within the plasma membrane Alternatively