Exocytosis occurs when a cell needs to get rid of something that is too big to get through the membrane. During exocytosis, a vesicle containing the stuff that the cell wants to expel moves to the membrane and fuses with it. As you can see, this allows the stuff out. Cells do exocytosis to get rid of large waste particles, or to secrete proteins or hormones (like insulin, for example) that need to be released outside of the cell. Here is an example of a real Paramecium (a small pond water organism), doing exocytosis. Credits: Music by Bensound (https://www.bensound.com/) Paramecium exocytosis courtesy of John S. Mead (used with permission). Link to original footage: https://www.youtube.com/watch?v=U9pvm_4-bHg