Does the sap vacuole serve a function?
The sap vacuole serves a few different functions, depending on the organism.
In general sap vacuoles do more in plants than they do in animals, and are also generally larger. They function as a generalized storage space, storing everything from salts to proteins to waste for the rest of the cell. They often store substances that serve a particular function unique to that particular species, such as pigments or toxins, because substances inside the cell sap are isolated from the rest of the cell. As a result of this, many substances we harvest from plants are stored in their sap vacuoles, including rubber and opium.
In non-woody plants the sap vacuole is also typically pressurized by turgor pressure, which presses against the cell wall and gives the plant cells more rigidity.