What is phagocytosis?

Phagocytosis is a process by which certain living cells called phagocytes engulf or ingest other cells or materials as a defense mechanism. Phagocytes are a type of white blood cells and the materials that they ingest are dead cells and other foreign substances such as bacteria. 

In humans, phagocytosis occurs when a living cell attempts to destroy infected cells, harmful pathogens such as bacteria, and other foreign particles by surrounding them in lytic enzymes. This is a crucial aspect of the immune system as it protects the body from these harmful substances. By engulfing and destroying the dead cells and pathogens, phagocytosis stops the spread of infection or pathogens in the body.

Phagocytosis is typically carried out by special immune system cells such as neutrophils and macrophages. For phagocytosis to happen, the macrophage or neutrophil needs to come in direct physical contact with the pathogen or dead cells in order to bind to the item it wants to engulf. When the pathogen comes in physical contact with the phagocytic cell, the latter surrounds the particle by forming pseudopodia all around it. The plasma membrane is then pinched off into a phagocytic vesicle known as a phagosome. 

In single-celled organisms such as amoeba, phagocytosis is used as a means of ingesting food particles.