STPM Biology Biological Molecules (Part 23)

Movement of Substances through Membrane 3

Endocytosis and Exocytosis

Moving bulk quantities of large ions or molecules through cell membrane is done using endocytosis and exocytosis. Macromolecules and large particles are taken into the cell by endocytosis and discarded through exocytosis.

Endocytosis and exocytosis

Endocytosis

• endocytosis = the uptake of substances into cell through invagination of the plasma membrane.
• if the substance taken in is a solid, the endocytosis is called phagocytosis. 
• Phagocytosis is the uptake of solid substances into cell through the invagination of the plasma membrane.
• example of phagocytosis in living cells:
• Amoeba engulfing of food particles.
• White blood cells engulfing bacterium.

• If the substance taken in is a liquid, the endocytosis is called pinocytosis. 
• Pinocytosis is the uptake of liquid by cells through the invagination of the plasma membrane.

Phagocytosis and pinocytosis

The importance of endocytosis:
1. endocytosis allows cell to take in large particles and macromolecules.
2. endocytosis enable bulk transport of macromolecules.
3. enable cells to take in specific molecules.

Here I will just explain the part of endocytosis. You know why? Exocytosis is just an opposite process of endocytosis….