The vacuole is the site where a cell membrane comes into contact with water. A vacuole, which is an organelle found in a cell's cytoplasm, has a membrane called a tonoplast that surrounds it. The function of this membrane is as a barrier between the salty fluid of the cytoplasm and the contents of the vacuole.
Both animal and plant cells contain vacuoles. In plant cells, vacuoles may function as storage areas for water. These storage areas also provide the food and other nutrients necessary for a plant's survival. Another function of the vacuole is to hold waste products and break it down. In regards to the difference in the vacuole size of plant and animal cells, plants cells have bigger vacuoles.