Pinocytosis and exocytosis
A lot of molecules essential to life are too large to simply cross the plasma membrane, or even pass through protein channels embedded within. The way these are transported is by being enveloped in lipid bubbles that join with the main membrane and open up to release the content to the other side of the membrane (pinocytosis – a form of endocytosis). Conversely, a bubble, called vesicle, already in the cytoplasm can merge with the plasma membrane and release its content on the outside (exocytosis). This process does use energy (ATP, see next headings).
Pinocytosis and exocytosis are reverse processes, involve the fusion of vesicles with the plasma membrane, and transport large amounts, hence being methods of bulk transport.
Endocytosis refers to any generic process of forming a vesicle on the inside of a cell, while pinocytosis is the specific case when these vesicles go on to fuse with…