Vacuoles are membrane-bound organelles that store various materials within a cell. They are found in both plant and animal cells. In plant cells, vacuoles occupy a large portion of the cell's volume and maintain the cell's shape and turgidity. They also store various substances such as water, salts, sugars, proteins, and waste products. In animal cells, vacuoles are smaller and may have different functions, such as storing food, waste products, or other substances necessary for cellular processes.