Question

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

Answer 1

Correct Option (b) disappear

Explanation:

Freshwater 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 disappear because the process of endosmosis does not happen and thus, water does not come in the protoplasm.