Q. What is endocytosis and exocytosis?
Ans- Endocytosis: Endocytosis is the ingestion of material by the cells through the plasma membrane. It is a collective term that describe two similar processes: Phagocytosis (cell eating), potocytosis or pinocytosis (cell drinking). Both require energy so may be regarded as different forms of active transport.
- Phagocytosis: It literally means “cell eating”. It is common method of feeding among the protozoa (amoeba) and lower metazoa (sponges). White blood cells (leucocytes) engulf cellular debris and uninvited microbes (virus, bacteria) in the blood by phagocytosis.
- Pinocytosis or potocytosis: It is the bulk transport of fluid matter and substances dissolved in it (e.g. ions, sugar, amino acids) across the cell membrane by forming minute detachable vesicles. Pinocytosis is also called cell drinking.
Exocytosis: Just as materials can brought into the cell by invagination and formation of a vesicle, the membrane of a vesicle can fuse with the plasma membrane and extrude its contents to the surrounding medium. This is the process of exocytosis. Exocytosis occurs in various cells to remove undigested residues of substances brought in by endocytosis, to secrete substances such as hormones, enzymes and to transport a substance completely across a cellular barrier.