A vacuole is a membrane-bound organelle. They are a kind of vesicle. Vacuoles are closed sacs, made of membranes with inorganic or organic molecules inside, such as enzymes. They have no set shape or size, and the cell can change them as needed. They are in most eukaryotic cells and do many things. They can store waste. Vacuoles and their contents are distinct from the cytoplasm, and are classified as ergastic according to some people. The solution that fills the vacuole is called cell sap.