Question

ou swished your mouth with 0.9% NaCl (saline solution), which is the approximate concentration of NaCl inside your cells, why would 0.9% NaCl be preferable over using deionized water to isolate cheek cells?

Answer 1

Before proceeding with the solution, let me tell you the very basics of water movement.

Water always moves from Its higher water potential to its lower one. In other words, water always moves from hypotonic to hypertonic solution. Pure water has a psi (water potential) value of 0.(It is maximum).

0.9 % NaCl is a physiological saline, which is isotonic with the the cell's interior conditions.

So, there will be no net loss or gain of water in or out of Cell. so the the cell will neither swell or shrink.

Our cells are animal cells and lack a cell wall.

De-ionized (De- Removal, Ionized- Ions) as the meaning suggests this water lacks ions(+or -). so if this water will be used it will create a hypotonic conc. and the cells interior will be hypertonic(more salt conc.).

This will cause the water to be taken up by the cell, resulting in swelling and bursting.

That's why 0.9% NaCl is preferred over Deionized water.