Question

37. You are working in a laboratory, after graduation, since you have recently discovered a new process to allow nerve cells to regenerate after they have been saved in an injury. You resuspend your cells in a wash buffer that contains 140mM NaCI (58.44g/mol) 5 % glucose and 5mM KCI (74.55g/mol) pH 7.4.

Please answer whether the solution is hypo, iso, or hypertonic. What would happen to the cells. Explain why the answer is what it is. Explain which are the penetrating and nonpenetrating solutes.

Answer 1

To know wheather a solution is hypertonoc or isotonic we should first calculate the osmolarity of the solution

a) 140 mM Nacl = 140 * 2 = 280 mOsmol ( 2 because dissociation factor of Nacl = 2).

b) 5% glucose = 277 mOsmol.

Calculation : Molarity of Nacl = wt in grams / mol wt of glucose = 50 grams / 180 = 0.277 moles.

Osmolarity = molarity * dissociation factor = 0.277 * 1 = 0.277 Osmol ( dissociation factor of glucose = 1)

= 277 mOsmol.

c) 5mM kcl = 5 * 2 = 10 Osmol

So total osmolarity of the solution = 280 + 277 + 10 = 567 mOsmol.

Normal osmolarity is around 300 mOsmol, so this solution is hypertonic,

So when you place a cell in this solution (hypertonic solution), the cell volume will decrease and could shrink.

The reason why the cell shrinks,is because water flows from the cell to the outside by the process of osmosis because the outside being hypertonic.

Penetrating and non penetrating, refers to the ability of these solute particles to cross (go through) the membranes separating the solutions.

Penetrating solutes: solutes that can pass through a membrane. Example glucose is penetrating solid

Non-penetrating solutes: solutes that cannot pass through a membrane.Example, Nacl is non pentrating solid