A red blood cell with an osmolarity of 300 mOsM (non-penetrating solutes) swells but does not lyse when placed in a 300 mOsM solution. Therefore the solution is hypotonic to the cell the cell is hypertonic to the solution the solution could be 300 mOsM urea there is a mix of penetrating and nonpenetrating solutes in the solution. Designate each solution according to its osmolarity and tonicity, and explain what happens to the cells and why. A. 200 mOsM NaClB. 400 mOsM ureaC. 100 mOsM urea plus 200 mOsM NaClD. 300 mOsM urea

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Explanation:

A. 200 mOsM NaCl

This solution is hypotonic to the red blood cell (RBC) with penetrating solute. The RBCs will swell up and burst because the water will move into the cells.

B. 400 mOsM urea

This solution is hypertonic to the RBCs with non-penetrating solutes. Water will leave the cells via osmosis and the cells will shrink and appear shriveled.

C. 100 mOsM urea plus 200 mOsM NaCl

This time both penetrating and non-penetrating solute is present. The solution is isotonic to the RBCs and although there will be movement of water between the cells and the solution, there will be no overall change in the concentration of water for each and no change in appearance of the cells.

D. 300 mOsM urea

The RBCs will not lyse nor shrivel as again the solution is isotonic to the RBCs.