Red blood cells are a typical example used to explain tension. When the salt (ion) concentration in the blood cells is the same as the outside, the solution is isotonic with respect to the cells, and they assume a normal shape and size. If the extracellular solute is less than its internal solute, for example, if you put red blood cells into fresh water, the solution (water) is hypotonic relative to the interior of the red blood cells. When water is flushed into the cells in an attempt to bring the concentrations of the internal and external solutions the same, the cells swell and may rupture. Incidentally, because hypotonic solutions can cause cell rupture, this is one of the reasons why a person is more likely to be submerged in fresh water than fresh water. If you drink too much water, this is also a problem. If the extracellular solute concentration is higher than the intracellular concentration, if red blood cells are placed in the concentrated salt solution, the salt solution is hypertonic with respect to the interior of the cell. Red blood cells experience wrinkles, which means they shrink and shrink as the water leaves the cells until the solute concentrations are the same inside and outside the red blood cells. The tension of the handling solution has practical applications. For example, reverse osmosis can be used to purify solutions and desalinate seawater. Hypertonic solutions help preserve food. For example, packaging food in a salt or pickling in a hypertonic solution of sugar or salt creates a hypertonic environment that kills the microorganism or at least limits its ability to reproduce. Hypertonic solutions also dehydrate food and other materials as water leaves the cells or passes through the membrane in an attempt to establish a balance. The terms “hypertonic” and “hypotonic” often confuse students because they ignore the consideration of the learning framework. For example, if the cells are placed in a saline solution, the salt solution is more permeable (more concentrated) than the cellular plasma. However, if the situation is observed from inside the cell, it can be considered that the plasma is hypotonic to the brine.