Question

Are protozoans presenting contractile vacuoles (also called pulsatile vacuoles) more commonly found in fresh or in salt water?

Answer 1

Fresh water is the less concentrated of solutes than sea water and it (fresh water) tends to be less concentrated than the intracellular environment making cells to swell. Sea water,on the other hand, since it is very concentrated tends to dehydrate the cell. In certain organisms, usually single-celled organisms lacking a cell wall, there exists a special kind of vacuole, called a contractile vacuole. A contractile vacuole works just the same as the name suggests, in that it expands and contract.So the protozoans with the contractile vacuole are more commonly found in the fresh waters.

• In the fresh water forms, where the contractile vacuoles perform the function of osmoregulation, some soluble wastes are also expelled with the outgoing water.
• Some protozoans exhibit the presence of special vacuoles named contractile vacuoles. They keep pulsating so as to expel any excess water or solutes present in the protozoan body.
• The members of Sarcodina, Mastigophora and Ciliata possess these contractile vacuoles whereas all parasitic protozoans are devoid of the same (ciliates are exceptions)