In: Biology
Which of the solutions below is hyperosmotic, isoosmotic, and hypoosmotic relative to the Red Blood Cells (RBCs) BEFORE and AFTER blood is added?
0.15 M Urea
Before:
After:
What is the osmolarity before and after blood is added?
0.3 M NaCl + 0.3 M Urea
First part
Before adding blood, 0.15M urea is isoosmotic, as urea can penetrate cell membrane.
When red blood cells are placed in a 0.15 M urea solution, the urea (permeable solute) diffuses into the cells until its concentration on both sides of the cell membranes becomes equal. Quickly, as the solute can not pass out of the cell, osmotically active solute particles inside RBC cause osmosis and water enters the cell leading to burst of the blood cells. Thus after adding blood, urea solution becomes hypoosmotic as the osmotically active solutes (urea) are more inside the cells.
Osmolarity can be determined multiplying the number of particles (produced from dissolving the solution in water)
by molarity. Osmolarity tells whether the solution is hyperosmotic, isoosmotic or hypoosmotic compared to another solution.
Osmolarity of 0.15M urea is 1 X 0.15 = 0.15osmoles = 150 milli osmoles/L
[ Urea is not ionized in water, so the no. of particle is 1; and 0.15 is the molar mass given]
Before blood is added, the osmolarity of 0.15M urea is 150mosm/L.
Second part
Osmolarity refers to the concentration of all solute particle in a solution.
Osmolarity of 0.3M NaCl = 0.3 X 3 (molar mass X number of particles) = 0.6 osmoles/L= 60mosmoles/L
Osmolarity of 0.3 M urea= 0.3 X 1 = 0.3 osmoles/L = 30 mosmoles/L
So before adding blood, the osmolarity of 0.3M NaCl + 0.3M urea = 60 + 30 mosmoles/L
After adding blood, some amount of urea crosses the cell membrane and enters the cell until the equilibrium is reached.
Thus the osmolarity of the solution is less.
NaCl is not a permeable solute through the cell membrane, So RBC in 0.3M NaCl is in hperosmotic medium. (0.15M NaCl is isoosmotic and isotonic)
Before and after adding blood, it is hyperosmotic.