The S is short for synthesis, which means that DNA is being replicated. This is one of the stages of interphase, when the cell is growing and getting ready to divide. Well, this is the getting ready to divide part of interphase; the cell needs to duplicate its DNA so it has enough to divide out to daughter cells.
If it is more salty it means that the water is hypertonic to the hypotonic potato and if the water is less salty then the water is hypotonic to the hypertonic potato
