Question

When a fresh-water protozoan possessing a contractile vacuole, is placed in a glass containing marine water, the vacuole will

• A. Increase in size
• B. Decrease in size
• C. Increase in number
• D. Disappear

Answer 1

The correct option is D Disappear

Contractile vacuoles serves function of osmoregulation. In fresh water protozoa osmotic pressure of cell is more than outer environment and net movement of water is inside the cell. If there is excess movement of water inside the cell then cell will swell up and ruptures. Contractile vacuoles maintain this osmoregulation. In marine environment the cell is hypotonic, and it starts loosing water. So, if we keep fresh water protozoa in marine environment, then contractile vacuole disappears.

Thus, the correct answer is option (D).