Question

What is the difference between a semi-permeable membrane (parchment paper, cellophane paper, etc.) and a differentially permeable membrane (cell membrane)?

Answer 1

Cell membraines are cannot fully permeable, or else the concentrations of salts, sugars, and everything else would be all messed up within an organism. Instead, cell membranes are able to selectively permeate through channel, pumps, osmosis, diffusion etc. Whereas parchment paper and cellophane paper used for dialysis tubing works with liquids through diffusion and osmosis. Instead of actively transporting salts, per say, like within a living organism, these pieces of paper merely moves solvents or solutes from a low concentration to a high concentration or vice versa, aiming to equalize the concentration on both sides.

Answer 2

A semi permeable membrane allows diffusion on the basis of just the size of particles. For example, starch won't pass through as it is a macromolecule but glucose would as it is smaller in size.
On the other hand, a differentially permeable membrane would take factors other than the size too in consideration. For example, sodium ions won't keep entering cells because they are small; it depends on whether the cell needs them or not.

Answer 3

Sodium usually passes through membranes through pumps such as the sodium potassium pump.

Answer 4

and there is no pump in a semi permeable membrane or any other trans membrane carrier proteins

Answer 5

I meant that there are pumps in selectively permeable cell membranes. Sorry if there were any confusion.

Answer 6

Thanks! I got it now. :D