Question

In a dialyse machine there are two liquids separated by a permeable membrane. The idea of a dialysis machine is to get rid of certain substances in the blood which will be toxic if they get too concentrated.

1) what is one such substance?

2) describe how you would make up the composition of dialysis fluid to make sure that this potentially toxic substance is got rid of

The blood contains dissolved substances that you want to keep.

3) Give one example of such a substance

4) how you would make up the composition of dialysis fluid to make sure that the person having dialysis doesn’t loose this substance?

5) explain the principle (concept or idea) which results in blood not losing this substance

Answer 1

ANSWER 1)
One such substance would toxins such as Lithium, which should have been removed by a well-functioning kidney, but requires dialysis on the absence of one.

ANSWER 2)
We can make up the make up the composition of dialysis fluid to exactly resemble every other component of blood except this toxin, the concentration of this toxin in the dialysis fluid should be zero. This will ensure that this potentially toxic substance is got rid of.

ANSWER 3)
One such substance that would be dissolved in blood and should not be lost in dialysis is dissolved oxygen because it is essential for many activities.

ANSWER 4)
We can make up the make up the composition of dialysis fluid to have the exact same concentration of the dissolved substance that we want to keep as is its concentration in blood. This will ensure that this dissolved substance of need will not be able to diffuse through from the blood to the dialysis fluid.

ANSWER 5)
The principle (concept or idea) which results in blood no losing this substance is called isotonicity. Since the concentration of this item is the same on both sides, there exists no concentration gradient (driven by Brownian motion) to cause any transfer of material from the side with higher concentration to the side with lower concentration.
Thus making the dialysis fluid have the same concentration of the substance as blood, causes there to be no concentration gradient which is the driving force for diffusion.