When a sodium chloride (NaCl) solution is given to some intravenously (as an IV directly into the blood), it is usually a 0.9% NaCl solution. The reason is that a 0.9% NaCl is isotonic to your red blood cells. Use that information to answer the following questions: In the solution above, which molecule is acting as the solute and which molecule is acting as the solvent? If you replaced the 0.9% NaCl solution with pure water instead, would the water be hypertonic, hypotonic, or isotonic to your red blood cells? If you replaced the 0.9% NaCl solution with pure water instead, would the net (overall) movement of water be into the cell, out of the cell, or would there be no net movement of water? If you replaced the 0.9% NaCl solution with pure water instead and waited, what specifically would happen to your red blood cells?

(2) If the NaCl is replace with water, the water content will become hypotonic to the red blood cells as there would be less solute in the solution than in the cell's cytosol. This also means there is more water in the solution than in the cell's cytosol.

(3) Because the water is hypotonic to the red blood cells (as described in (2) above), the net movement of water will be into the cell.

(4) If the movement of water is allowed to continue as described in (3) above (i.e if 0.9% NaCl in the solution is replaced with pure water instead and waited), the cell will rupture which can lead to cell lysis or cytolysis.

NOTE: An isotonic solution describes when there is the same amount of solute in the cell and the solution outside the cell hence there is little or no movement of water.