Biology 2009 JAMB Past Questions - Question 31: A marine protozoan is likely to have no contractile vacuole mainly because the cytoplasm is

Correct Answer

A

Explanation

AThecell content of a protozoan like Amoeba is hypertonic to fresh water likeriver. Amoeba draws in water into the body. It therefore develops contractilevacuole for eliminating the excess. When the contractile vacuole reaches itsmaximum size, it bursts to eliminate the excess water. A new contractilevacuole is formed. However, the frequency of the filling and discharging of thecontractile vacuole decreases as the salinity of the .qiuatic environment increases.Thus, the cell content of a marine protozoan is isotonic to the sea water thathas equal osmotic concentration and therefore exerts equal osmotic pressure.