Phagocytosis is the process in cell biology in which a cell engulfs a large particle, such as a bacterium, by extending its plasma membrane around it to form an internal phagosome. It is a type of endocytosis and is used both for feeding, especially by many protists, and for defence in multicellular organisms. The phagosome may fuse with lysosomes to form a phagolysosome, where enzymes and antimicrobial chemicals break down the engulfed material. In the immune system, phagocytosis is carried out by cells such as neutrophils, macrophages and dendritic cells, which remove pathogens, dead cells and debris. These cells are classed as phagocytes. This video, captured through a optical microscope and played back at eight times speed, shows a neutrophil in a drop of human blood engulfing a bacterium through phagocytosis.

Video credit: Andrei Savitsky