Exocytosis is by

Ans: d (Expulsion) Ref: Ganong 22nd ed/p. 28-30Exocvtosis:-Vesicles containing the material for export are targeted to the cell mem-brane, where they bond via the vsnare/ t-snare arrangement.The area of fusion then breaks down, leaving the contents of the vesicle outside and the cell membrane intact.This is a Ca2+ dependant process.Thus, there is a net increase in the surface area of the cell as the cytoplas-mic sides of two membranes fuse.Endocvtosis:-The process by which cells take up large molecules. In endocytosis, two non cytoplasmic sides of membranes fuse. Endocytotic vesicles are generated when segments of the plasma membrane invaginate, enclosing a minute volume of extracellular fluid and is contents. The vesicle then pinches off as the fusion of plasma membranes seal the neck of the vesicle at the original site of invagination.There are two general types of endocytosis:-a) Phagocytosisb) PinocytosisPhagocvtosis:-Involves ingestion of large particles such as viruses, bacteria, cells or debris.Occurs only in specialized cells such as macrophages and granulocytes.Pinocvtosis:-Property of all cellsIt is a cellular uptake of fluid and fluid contents.It is of two types:-Fluid phase pinocytosis is a non selective process in which the uptake of a solute is simply proportionate to its concentration in the surrounding extracellular fluid.Absoipti ve pinocytosis is a receptor mediated selective process primarily responsible for the uptake of mac- romolecules. The vesicles formed dur-ing absorptive pinocytosis are derived from invagination (pits) that are coated on the cytoplasmic side with a Filamentous material.In many systems, Clathrin is the filamentous material. For e.g., LDL is internalised by means of coated pits containing the LDL receptors.