Vacuoles

fig : Vacuoles

• The vacuole is the membrane-bound space found in the cytoplasm. It.contains water, sap, excretory product and other materials not useful for the cell.
• The vacuole is bound by a single membrane called tonoplast.
• In plant cells the vacuoles can occupy up to 90 per cent of the volume of the cell.
• In plants, the tonoplast facilitates the transport of a number of ions and other materials against concentration gradients into the vacuole hence their concentration is significantly higher in the vacuole than in the cytoplasm.
• In Amoeba the contractile vacuole is important for excretion. In many cells, as in protists, food vacuoles are formed by engulfing the food particles.