[kimi85]

Hi.

I have questions regarding this experiment where a drop of blood is placed in tubes with different salt concentrations. Why was the solution allowed to stand for 2 hours at room temp. My answer is because it takes 2 hours for water to enter or exit the cell or it takes 2 hours for water to have an effect on the cell volume. Is my answer correct? are there any other answers?

And why at room temperature? is it because the integrity of the cell is dependent on temperature..

thank you very much

[Yggdrasil]

Correct, you want the osmotic pressure to reach equilibrium and waiting for 2 hrs ensures that this happens.

The temperature is probably for convenience, although the permeability of the cell membrane is temperature dependent.  The most relevant temp for experimenting on RBCs is 37^oC because that's the temperature of their normal environment (the human body).

[kimi85]

thank you very much!

I have another question.
the concentration of the salt solutions were 2%, 0.9% and 0.5 %
Only the 0.5% was used to make different concentrations so that the final concentration will be different. Why is this so?
the 2% was also used only in one test tube and still of the same concentration and also of 0.9%.

thanks

[Padfoot]

Maybe you had to dilute one of the solutions to make one hypotonic.  The Osmolarity of RBC's are 300mOsm/L IIRC.

Edit:  Or more hypotonic