Endocytosis
During endocytosis the cell membrane folds inwards and fuses together surrounding the substance in a pocket. The pocket pinches off inside the cell and forms a vesicle. The vesicle fuses with a lysosome or a similar vesicle, and enzymes break down the membrane and its contents. In endocytosis there is one sub-type, called phagocytosis. Phagocytosis is when the cell membrane engulfs large particles. The word literally means “cell eating.” Phagocytosis plays a key role in your immune system. Some white blood cells called macrophages help your body fight infection. They find foreign materials, such as bacteria, and engulf and destroy them. In endocytosis, he cell engulfs some of its extracellular fluid. Including material dissolved or suspended in it. A portion of the plasma membrane is invaginated, coated with molecules of the protein clathrin, and pinched off forming a membrane-bounded vesicle called an endosome.