Endocytosis is a process for moving items that are outside of the cell into the cytoplasm of the cell. Exocytosis is a process for moving items from the cytoplasm of the cell to the outside. Both endocytosis and exocytosis vary from the other forms of membrane transport, because materials do not cross through the lipid bilayer. Instead, items being moved into or out of the cell are engulfed by entire sections of the membrane lipid bilayer. They are being swallowed up or spit out by the membrane so to speak.

Endocytosis involves the movement of materials into the cell using ATP energy. The energy is used to alter the shape of the membrane surface. The shape change is called invagination and results in the material outside the cell being engulfed by the entire membrane. (Like sticking your finger into a balloon). When the material is completely surrounded, the membrane pinches together forming a vesicle inside the cytoplasm of the cell. View endocytosis animation.

Endocytosis of large particles is called phagocytosis. You may recognize this term from your Biology 11 course, as the way an Amoeba obtains its food. In our bodies, various types of white blood cells ingest foreign particles and bacteria by phagocytosis.

Endocytosis of small particles is called pinocytosis. An example of this process is the absorption of small nutrient particles into the villi of the small intestine by "sipping".

Exocytosis involves the movement of materials out of the cytoplasm of the cell using ATP energy. This process looks like endocytosis played backwards. So in this case, a vesicle or vacuole (large vesicle) migrates to the membrane inner surface and fuses with the cell membrane. Then energy is used to alter the membrane shape and merge the vesicle with the cell membrane and force the contents of the vesicle to the outside of the cell. This process of exocytosis is how the cells of glands, that produce enzyme proteins or steroids, export molecules for use in other areas of the body. For example, proteins made in salivary glands act in the mouth and pancreatic enzymes act in the small intestine. View exocytosis animation.