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A unicellular protist X, which has contractile vacuole to remove excess intracellular water, was placed in salt solution of increasing osmolarity. The given graph shows the rate of contraction of vacuole to pump out excess water against osmolarity of solution.

Select the option that gives the correct explanation of the data.

 

A) In an isotonic solution there is no diffusion of water in or out of the X, so the contraction rate is zero.

B) At higher osmolarity, more salt diffuses into X, therefore lower rates of contractions are required.

C) The rate of contraction increases as osmolarity decreases because amount of water entering X by osmosis increases.

D) The contractile vacuole is less efficient in solution of high osmolarity because of reduced respiration and less production of ATP.