When a freshwater protozoan possessing a contractile vacuole is placed in a glass containing marine water, the vacuole will
A. increase in number
B. disappear
C. increase in size
D. decrease in size

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Correct Answer - D
(b) Fresh water protozoans live in hypotonic environment 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 proce4ss of endosmosis does not occur and thus, water does not come in the protoplam.

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