Question

When a fresh-water 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

Answer 1

Correct Answer - B
Freshwater protozoans live in hypotonic solution so, for regulation fo excess of water which comes in the protoplasm through the process of endosmosis, contractile vaculoes have developed.
when thses protozoans are placed in marine water, i.e., hypertonic water the contractile vecuoles disappear because the process of endosmosis does not happen and thus, water does not come in the protoplasm.