Osmolarity and tonicity

[candiishop]

Hi..

 

I having trouble answering this question. Any input would be greatly appreciated =)

 

Explain why the size of red blood cells stored in 0.15M urea would differ significantly from cells stored in the same concentration 0.15M of Na Cl? (Hint: work out the osmolarity and tonicity of the 2 solutions and compare each solution to the intracellular fluid of the erythrocyte(Red blood cells)

 

This is what I done so far... not sure whether it's right or not.

 

Osmolarity

Urea: 0.15 x 1000 = 150mOsM

Salt [Na Cl]: 0.15 x 2 (the sodium and the chloride ions dissociate and 2 particles formed) x 1000 = 300 mOsM

 

Tonicity

Urea: cell bigger (swell) and becomes normal... isotonic solution

Salt: Smaller

[candiishop]

Another question... (sorry such a clueless in this topic)

 

Predict what would happen to erythrocytes placed in a solution containing 300mOsm/L urea and 300mOsm/L sucrose (i.e. a total of 600mOsm/L of particles in one solution; and remember that this is NOT made by mixing equal volumes of 300mOsm/L urea and 300mOsm/L sucrose). Fully explain your answer.

 

My draft response:

 

As urea can pass through the membrane and the sucrose can't. 150mOsm of the urea will pass into the cell making the cell a total of 450mOsm...