Question

We could have used any type of material for osmosis. Why do we need a semi-permeable membrane?

• A. So that solute particles can pass through
• B. So that the solution is stable
• C. To obstruct the solute particles
• D. To obstruct the solvent particles

Answer 1

The correct option is C To obstruct the solute particles

The membrane has to be semipermeable so as to obstruct the solute particles and selectively allow the smaller solvent particles to pass through. This is the basis of the process of osmosis.

Deeper explanation:
If you have pondered enough about osmosis, you should feel slightly confused. This is because we are quite acquainted with the process of diffusion in our daily lives. We usually see particles moving from a region of high concentration to a region of lower concentration, like an ink dropped into water.
But in osmosis, we observe that the solvent particles actually flow from a region of lower solute concentration to a higher solute concentration. The goal is to even out the concentrations in the two regions.
For this to happen, it becomes necessary to obstruct the flow of solute particles. To achieve this, the semi-permeable is designed in such a way that the spaces in the membrane are enough for the solvent particles to flow but not the solute particles.
If both solute and solvent particles were allowed to flow, we would have our diffusion process.