What process involves the engulfing of particles by the cell membrane?

The correct response is endocytosis, which includes the broader process of cells taking in materials from their surroundings. Endocytosis is a vital function that allows cells to internalize substances, such as nutrients and other molecules, by engulfing them with the cell membrane.

This process occurs through several specialized mechanisms depending on the type of substance being engulfed. In the case of larger particles or pathogens, cells utilize phagocytosis, where the cell membrane extends around the particle, enclosing it in a vesicle. Similarly, for liquid materials, pinocytosis occurs, allowing the cell to take in small droplets of fluid.

Overall, endocytosis is the overarching term that encompasses various specific forms of particle engulfing, such as phagocytosis and pinocytosis, making it the most accurate answer.