* Hypertonic solutions have a higher concentration of solutes (like salts) than the cell's internal environment.

* Hypotonic solutions have a lower concentration of solutes than the cell's internal environment.

* Isotonic solutions have the same concentration of solutes as the cell's internal environment.

Pure water has almost no solutes, whereas red blood cells have a certain concentration of dissolved ions and proteins. Therefore, pure water has a lower solute concentration than red blood cells.

What happens when red blood cells are placed in pure water?

Water will move from the area of high concentration (the pure water) to the area of low concentration (inside the red blood cells) through osmosis. This influx of water will cause the red blood cells to swell and potentially burst, a process called hemolysis.