Which process specifically refers to the engulfment of solid particles by a cell?

Phagocytosis is the process specifically defined as the engulfment of solid particles by a cell. During this process, a cell extends its membrane around the solid particle, effectively "swallowing" it and forming a vesicle called a phagosome. This mechanism is commonly seen in immune cells, such as macrophages, allowing the body to eliminate pathogens and debris.

In contrast, pinocytosis involves the ingestion of liquid and dissolved substances rather than solid particles. Exocytosis refers to the process through which substances are expelled from a cell by vesicles fusing with the cell membrane. Diffusion, on the other hand, is a passive movement of molecules from an area of higher concentration to an area of lower concentration, rather than a cellular engulfing process.

Understanding these differences is crucial, as each of these mechanisms plays a distinct role in cellular function and transport processes.