What is the difference between a semipermeable membrane and a selectively permeable membrane?

Question

I thought they were the same thing, but it's not according to my teacher. So, what is the difference anyways? I'm confused

Answer 1

They are approximately the same.

A semipermeable membrane doesn't allow certain solutes to pass through it. In practice, usually this has to with the size of the solute. So for example if you have a dialysis bag, it will have a semi-permeable membrane that will allow water, glucose, Na+, to move freely through its pores but not proteins, starch, DNA etc.

A selectively permeable membrane again doesn't allow certain molecules to pass through it, but the criteria are more than just size. It "selects" which type of molecule it will allow to pass. E.g. the cell membrane might allow water molecules to move through it, but Na+ which is not so much bigger doesn't move freely (its movement is regulated by the cell).

You could say that the term semipermeable is more general and selectively permeable membrane is a term for a certain type of a semipermeable membrane.

Answer 2

The two are actually quite similar, but in terms of the selectively permeable membrane, only certain substances are allowed to pass through than others while in the case of a semipermeable membrane, is only permeable to water..

Answer 3

semipermeable membrane allows only ions to pass not the other part of solution


and permeable membrane allow to specific ions or solution to pass through it