Permeability of Red Blood Cells - Urgent!!?

Question

permeability of rbc membrane to different solutes can be gauged by whether or not the cells haemolyse when placed in isosmotic solutions of the solute. What does this mean?

Is it that the cells are placed in the isosmotic solution .. then both have the same number of active particles but they may have different types of active particles and may have different concentrations of water.???

And I don’t understand how can this help us understand the permeability of rbcs to different solutes??

I know that the solutions of glucose, sucrose and NaCl are isotonic because there was no haemolysis therefore no movement of water.

But the 0.28 M urea solution, it haemolysed the rbc, which tells us that it is permeable to the cell membrane of the rbc. I don’t understand why this happens at all… so if urea is permeable then diffusion should occur and not osmosis .. why does haemolysis occur?…. I am so confused!!!

And could also please explain to the 1.0M urea solution, where haemolysis also occurred - but took longer than the 0.28M urea

Answer 1

Firstly CALM DOWN.  You sound like your wigging out, and that won't help your understanding of this.  

Each solution is either hyper, hypo, or isotonic.  Using your RBC, the solution with 0.28 M urea is hypertonic (the area outside the membrane has a higher concentration then the area inside the membrane).

The urea didn't go anywhere since it can't cross the membrane. (Osmosis is movement of water from an area of low concentration to an area of high concentration.  That's why it isn't diffusion.)  Water moved from within the cell to the outside of the membrane causing the RBC to "shrivel up and die."

I'm not sure why the 1.0 took longer than 0.28, perhaps I don't understand the concentration properly.

btw, it's spelled "hemolysis"