Endocytosis ( endo = internal, cytosis = transport mechanism) is a general term for the various types of active transport that move particles into a cell by enclosing them in a vesicle made out of plasma membrane. There are variations of endocytosis, but all follow the same basic process.

Due to their structure, clathrins, when stimulated, naturally bond to one another to form cages around the ingested molecules. Macropinocytosis is the process of ingesting larger molecules, and is activated when the cell membrane undergoes cell surface ruffling, or structural reformation of the membrane.