Vacuoles | Definition, Structure & its Functions
Vacuole is the membrane-bound space found in the cytoplasm. It contains water, sap, excretory products and other material not useful for the cell. These are also called sap vacuoles.
In plant cells, the vacuoles can occupy upto 90 percent of the volume of the cell. They are bounded by a single, semipermeable membrane called tonoplast. This membrane facilitates the transport of a number of ions and other materials against concentration gradients into the vacuole. Thus, their concentration is significantly higher in the vacuole than in the cytoplasm.
Types of vacuoles:
(a) Contractile vacuole : In Amnoeba, it helps in excretion.
(b) Food vacuoles : In many cells, as in protists, food vacuoles are formed by engulfing the food particles.
(c) Gas vacuoles (Pseudovacuoles): These are membraneless vacuoles found in prokaryotes provide buoyancy.