Which option best explains the term 'phagocytosis'?

Phagocytosis is a specific type of endocytosis in which cells, particularly immune cells like macrophages and neutrophils, engulf and internalize large particles, such as pathogens, dead cells, or debris. This process is vital for the immune response, as it allows the body to eliminate harmful invaders and maintain homeostasis.

During phagocytosis, the immune cell identifies a pathogen, extends its membrane around it, and envelops it, forming a phagosome. This phagosome then typically merges with a lysosome, which contains enzymes that break down the engulfed material, aiding in its destruction. Therefore, the engulfing of pathogens by immune cells is fundamental to the body's defense mechanisms.

The other options refer to different biological processes: the release of hormones involves signaling in the endocrine system, the production of antibodies relates to the adaptive immune response, and the differentiation of stem cells pertains to developmental biology and the formation of specialized cell types. Each of these processes serves distinct roles in biology, highlighting the unique function of phagocytosis within the immune response.