Endocytosis is the process where a cell imports large things into the cell. All forms of endocytosis are active, meaning the cell expends ATP while performing this process. Specifically, a style of endocytosis called phagocytosis involves a cell surrounding the target material with its cell membrane and encloses it while bringing it into the cell. This enclosed membrane bound material then pinches off into a spherical 'vesicle'. An example of this can be a cell importing a protein into its cellular space.