A vesicle in biology is a small organelle within a cell consisting of fluid enclosed by a membrane is a small membrane-enclosed sac that can store or transport substances. When prepared artificially they are generally called liposomes. They can be formed from a wide variety of surfactants including simple fatty acids and mixtures of fatty acids and fatty alcohols. In living organisms, most vesicles have specialized functions depending on what materials they contain. Vesicles are used in the cell to store, transport, or break down cellular products and waste. The membrane enclosing the vesicle is similar to that of the cell membrane, and vesicles can fuse with the plasma membrane to release their contents outside of the cell, in a process known as exocytosis. Vesicles can also fuse with other organelles within the cell.