Phagocytosis is the ingestion or engulfing of some foreign particle or cell by a phagocytic cell to form a food vacuole. Phagocytic cells are either one-celled organisms or one of the body cells, such as a white blood cell. Bacteria, dead tissue cells and dust particles are all examples of particles that may be phagocytosed.
Phagocytosis is found only among eukaryotes. Lower life forms use phagocytosis as a means of feeding, whereas higher species use it to fight infection. Many protists obtain part or all of their nourishment by phagocytosis of smaller organisms, called phagotrophic nutrition to distinguish it from nourishment by absorption, which is called osmotrophic nutrition.
Macrophages, a type of blood cell, consume pathogens by phagocytosis. Along with granulocytes, macrophages are one of the most effective phagocytic cells in vertebrates. Granulocytes are smaller phagocytes, and a type of white blood cell. Macrophages and granulocytes move towards the infected areas, where they engulf bacteria. Virulent bacteria may need to be coated with antibodies before it is possible to phagocytose them, showing the importance of antibodies in fighting infection.
In many cells, phagocytosis takes place by surrounding the target object with pseudopods. In others, food particles are swept into a particular cavity within the cell, called a cytostome or mouth. In both cases, it ends up in an intracellular chamber, called a vacuole, which may be merged with lysosomes containing digestive enzymes. Once the object has been broken down, the resulting matter is absorbed into the cytosol.