Paramecia are unicellular protists that have contractile vacuoles to remove excess intracellular water. In an experimental inves
tigation, paramecia were places were placed in salt solutions of increasing osmolarity. The rate at which the contractile vacuole contracted in pump out excess water was determined and plotted against osmolarity of the solution, as shown is the graph. (Graph has negative slope; y-axis - rate of concentration, x-axis - osmolarity of solution.) Which of the following is the correct explanation for the data? a. At higher osmolarity, lower rates of contraction are required because more salt diffuses into paramecia
b. The contraction rate increases as the osmolarity decreases becase of the reduced amount of ATP produced by cellular respiration
c. The contractile vacuole is less efficient in solutions of high osmolarity because of the reduced amount of ATP produced from cellular respiration
d. In an isosmotic salt solution, thre is no diffusion of water into or out of the paramecia, so the contraction rate is zero
