Question

How are endocytosis and exocytosis similar? How are they different?

Answer 1

They are both bulk transportation methods of substances. However, exocytosis is the movement of substances out of the cell whereas endocytosis is the movement of substaces into the cell.

Explanation:

Both endocytosis and exocytosis involves the movement of large molecules into or out of the cell. Note that all bulk transport processes involve the use of energy. Materials transported through endocytosis and exocytosis are too large for diffusion.

Endocytosis
Endocytosis refers to the active movement of materials into the cytoplasm of cells through vesicles.
there are three types of endocytosis.

1) Phagocytosis

• occurs when cell engulfs *large molecules, solid particles or other cells * by wrapping pseudopodia (fake feet) around it and packaging it within a membranous sac called a food vacuole
• the particles will be digested after food vacuole fuses with a lysosome containing hydrolytic enzymes
  E.g.white blood cells engulf and destroy invading foreign bacteria.
• note that phagocytosis discriminates between different types of particles, and only take in specific materials

2) Pinocytosis

• occurs when cell takes in extracellular fluid or suspension into its cytoplasm in small vesicles
• it is not fluid itself that is needed by the cell, but rather the molecules dissolved in the fluid
• is not selective in substances it transports

3) Receptor-mediated endocytosis

• occurs when a cell takes in bulk quantities of specific substances, even though these substances may not be very concentrated in the extracellular fluid
• specific receptor-mediated proteins are embedded in the membrane exposed to the extracellular fluid
• specific substances bind to the receptor proteins
• the pit where the receptor proteins sit in are deepened and eventually seals, and enter the cells

4) Exocytosis

Exocytosis refers to the active movement of bulk materials out of the cytoplasm of a cell through vesicles

• secretory cells manufacture and export secreted products
• secretory products are accumulated in Golgi bodies, where they are packed into secretory vesicles
• vesicles move to the surface of cells where their membranes fuse with the cell surface membrane to discharge contents to the exterior of the cell

In a nutshell, 'endo' refers to the entrance of large molecules whereas 'exo' refers to the exit of large molecules.