One goes in the other goes out or vice-versa. Exocytosis is the term applied when transport is out of the cell. Note the vesicle on the left, and how it fuses with the cell membrane on the right, expelling the vesicle's contents to the outside of the cell. Endocytosis is the case when a molecule causes the cell membrane to bulge inward, forming a vesicle. Phagocytosis is the type of endocytosis where an entire cell is engulfed.
Pinocytosis is when the external fluid is engulfed.
Receptor-mediated endocytosis occurs when the material to be transported binds to certain specific molecules in the membrane. Examples include the transport of insulin and cholesterol into animal cells. Image from W.H. Freeman and Sinauer Associates, used by permission. Describe the general structure of a phospholipid molecule and what makes it suitable as a major component of cell membranes. Explain the behavior of a great number of phospholipid molecules in water.