A) osmoregulation is done by cell membrane
B) they are hypoosmotic to their environment
C) they are isotonic with their environment
D) their small body cannot accommodate it
Correct Answer: B
Solution :
The function of contractile vacuole is hydrostatic or osmoregulatory. Water in freshwater Protozoa enters the organism by endosmosis. The reason is that cytoplasm of a freshwater protozoan represents a medium denser than surrounding water and outer most plasmalemma or pellicle acts as a semi permeable membrane. Thus water continuously flows inside to dilute the cytoplasm. In marine environment protozoans need to conserve water. Hence, to minimize loss of water it lacks contractile vacuole i.e, they are hypoosmotic to their environment.
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