Vacuoles and vesicles function to move material around plant and animal cells through membrane-bound sacs. Plant cell vacuoles are large central structures that contain cell sap and help regulate water flow via osmosis. They aid in food and water storage. Animal cells contain smaller vacuoles and vesicles, as well as lysosomes, which are vesicles containing digestive enzymes that function as the cell's "cleanup crew" and digest macromolecules and old organelles. Lysosomes fuse with food vacuoles to digest polymers into monomers for use as cell nutrients. They are also involved in programmed cell death processes.