text: what is the definition of vacuole?   vacuoles are membrane-bound sacs within the cytoplasm of a cell that function in several different ways. in mature plant cells, vacuoles tend to be very large and are extremely important in providing structural support, as well as serving functions such as storage, waste disposal, protection, and growth. many plant cells have a large, single central vacuole that typically takes up most of the room in the cell (80 percent or more). vacuoles in animal cells, however, tend to be much smaller, and are more commonly used to temporarily store materials or to transport substances.