A vacuole is an organelle filled with liquid and surrounded by a single membrane called the tonoplast. The central vacuole in plant cells takes up to 90 percent of the cell volume and has a balloon shape. Contractile vacuoles display a star shape.
Vacuoles function as storage sites for toxins, waste, food, gases and other products of cellular activity. The central vacuole provides structural stability to plants by increasing the cell's turgidity and its state of fullness. Plants grow by the elongation of their cells as opposed to cell reproduction.
Contractile vacuoles reside on the membrane surface of paramecium. A vacuole absorbs fluids through micro filaments formed into canals. Then the vacuole constricts and forces the liquids out of the vacuole and cell. Gas vacuoles exist in some aquatic bacteria, providing buoyancy.