In endocytosis, a eukaryotic cell engulfs material to absorb it. There are 2 main types of endocytosis, distinguished by vesicle size and cellular machinery involved.
Cells drink via pinocytosis. The vesicles are small: convex pits for fluid collection and modest molecular uptake.
Pinocytosis is indiscriminate. Whatever chemicals are in the water are taken in.
Via phagocytosis, cells gobble large particles, be they cell debris or entire microorganisms.
While all cells continually ingest via pinocytosis, phagocytosis is a specialty act. In multicellular organisms, only specialized cells wolf down large chunks. For instance, immune system macrophages defend their organisms by swallowing microbial invaders.
Single-celled eukaryotes eat by engulfing their prey. For amoebas and protozoa, phagocytosis is a fancy term for dining.
In multicellular eukaryotes, endocytosis can play a crucial role in conforming a cell; driving shape changes by remodeling the cell membrane. This is one of many ways that the environment can influence cell development.