Q. What are the plant cell vacuoles? And what are their functions? And 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 proteins and carbohydrates. In young plant cells many small vacuoles can be seen within adult cells the most part of the interior area of the cell is occupied by a central vacuole.

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

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