When a fresh water protozoan is placed in marine water
Fresh water protozoans live in hypotonic solution so, for regulation of excess of water which comes in the protoplasm through the process of endosmosis, contractile vacuoles have developed, When these protozoans are placed in marine water i.e., hypertonic water, the contractile vacuoles become disappear because the process of endosmosis does not happen and thus, water does not come in the protoplasm.