The functions of a cell is most likely similar to the organism itself since the organism itself is made up of the cells which is performs the tasks and similarly the organism performs them in a macroperspective while cells, microscopically.
In the given situation such as excretion of waste can be done by either the digestive enzymes by some cells but other cells that doesn't have digestive organelle such as peroxisomes, they are carried from the internal organelles of the cell to the cell membrane then outside, an organelle functions for that. In the same manner, an organism has a excretory system that does its job, to excrete and defecate toxic materials.
