Osmoregulation is essential to all organisms as it maintains homeostasis of the organism's water content.
Osmoregulation in unicellular freshwater organisms like amoeba and paramecia involves an organelle called the contractile vacuole, which collects excess water as it accumulates in the cell and pumps it out. The graphs below plot contraction rate in contractile vacuoles vs. surrounding solution concentrations.
Which of the following statements best explains the response when Paramecia are placed in a beaker of distilled water to which a 5% NaCl solution is added dropwise?