A student wants to study red blood cells beneath a microscope. She is not sure which solution she should use to observe such cells. In solution A, she sees figure A (plasmolysis) and in solution B she sees nothing. Can you explain her observations?

Solution A - plasmolysis. The red blood cells were in an hypertonic solution (solution had a lower water potential than the red blood cells due to increased concentration of solute) thus water molecules move out of the cytoplasm of the RBC via osmosis across the semi permeable membrane, down the water potential gradient, giving appearance of shrivelled cells.
Solution B - the red blood cells are in a hypotonic solution; the solution has a higher water potential than the cytoplasm of the red blood cells due to a lower concentration of solute. Thus water molecules move into the cytoplasm of the RBC via osmosis down the water potential gradient. Red blood cells only have a thin cell membrane and thus burst as the water molecules move into the cell.