Describe the process of phagocytosis.

Phagocytosis begins when white cells called phagocytes recognise bacteria invading the body (pathogens). The cell membrane of one of these phagocytes then fuses around a single bacterium, engulfing it within a cellular compartment, which is then called the phagosome. This phagosome then fuses with a lysosome, which contains acidic enzymes and toxic chemicals, forming a phagolysosome. These enzymes and chemicals then break down and digest the bacterium, destroying it. After the bacterium has been destroyed, the macrophage absorbs any of the material that is useful and gets rid of the rest.