endocytosis
There are four main ways that molecules can pass through a phospholipid membrane. The first way requires no energy input by the cell and is called simple diffusion. This type of transport includes passive diffusion and osmosis. No assistance by a transport is necessary in simple diffusion. Facilitated diffusion, does involve the assistance of transport proteins. The third way, called active transport , requires that the cell uses energy to pull in or pump out certain molecules and ions. Active transport involves proteins known as pumps. The fourth way is through vesicle transport , in which large molecules are moved across the membrane in bubble-like sacks that are made from pieces of the membrane. Vesicular transport includes exocytosis and endocytosis.