Question

What are vacoules? Name their types and functions.

Answer 1

Vacuoles are non-cytoplasmic areas present inside the cytoplasm which are separated from the latter by specific membranes. Vacuoles are believed to be formed by expansion and pinching off from ER. Depending upon the contents and functions, vacuoles are of four types - sap vacuoles, contractile vacuoles, food vacuoles and air vacuoles.

1. Sap vacuoles: They are fluid-filled vacuoles or vesicles which are separated from the cytoplasm by a selectively permeable membrane called tonoplast. It has a number of transport systems for the passage of different substances. A number of small sap vacuoles occur in animal cells and young plant cells.
   
2. Contractile vacuoles: A contractile vacuole has a highly extensible and collapsible membrane. It is also connected to a few feeding canals. The feeding canals obtain water with or without waste products from the surrounding cytoplasm. They take part in osmoregulation and excretion.
   
3. Food vacuoles: They occur in the cells of protozoan protists, several lower animals, and phagocytes of higher animals. A food vacuole is formed by the fusion of phagosome and a lysosome. The food vacuole contains digestive enzymes with the help of which nutrients are digested.
   
4. Air vacuoles: They have been reported only in prokaryotes. An air vacuole not only stores gases but provide buoyancy, mechanical strength, and protection from harmful radiations.