vacuoles.

• Permanent vacuoles only exist in plant cells. Animal cells can contain temporary vacuoles but they are not common features.
• Cell vacuoles are fluid-filled sacs surrounded by a single membrane. Their size varies; in some cells the vacuole almost fills the cell. 

  The fluid is a dilute solution of molecules and ions. 
• The vacuole can be used to maintain the water balance of the cell, store mineral salts, amino acids, sugars and waste products. 
• The vacuole is important in keeping the cell firm. When the vacuole is full of sap the cell is said to be turgid.