What are plant cell vacuoles?

What are plant cell vacuoles? What are their functions? What is the covering membrane of the vacuoles called?

Plant cell vacuoles are cell structures delimited by membranes within which there is an aqueous solution made of various substances like carbohydrates and proteins. In young plant cells many small vacuoles can be seen; within adult cells the most part of the internal area of the cell is occupied by a central vacuole.

The main function of the vacuoles is the osmotic balance of the intracellular space. They act as “an external space” inside the cell. Vacuoles absorb or release water in response to the cellular metabolic necessities by increasing or lowering the concentration of osmotic particles dissolved in the cytosol. Vacuoles also serve as a storage place for some substances.

The membrane that delimits the vacuoles is called tonoplast, named after the osmotic function of the structure.