Illustration depicting the process of phagocytosis in three steps. Phagocytosis is a crucial process where immune cells engulf and eradicate harmful substances such as viruses and bacteria. In the first step, the bacterium is situated near the cell membrane. In the second step, the cell uses its membrane to bind to and engulf the bacterium. In the third step, a phagosome vesicle is formed around the bacterium, which then digests the ingested material.