Re: Why does red blood cells placed in distilled water swell then turn the

The red blood cells swell when placed in distilled water, because of osmosis. 
There are no salts or any other molecules dissolved in the distilled water,
but the red blood cell has many molecules dissolved in its cytoplasm.
Because Osmosis states that water tends to move toward regions where there
is more solute, the distilled water moves into the red blood cell throught
the plasma membrane, and the cell getts bigger/swells. If this happens for
too long, the red cells will actually burst (called Lysis) and die. The
Hemeglobin (protein that binds to oxygen we breathe to deliver the oxygen
to the cells in our body) in red blood cells is what makes them red, so
when the lysed cells spill the hemeglobin out into the water, it turns pink. 
I hope this helps,
Elena