Sugar and area can easily pass through semi-permeable (animal) membrane from their aqueous solutions but glue and gelatin, in their aqueous solutions, do not have free passage through it. Explain.

Explanation

Aqueous solutions of sugar and urea are true solutions while aqueous solutions of glue and gelatin belong to a colloidal system. In a true solution, particle size of the solute is of the order `10^(-8)`cm while in a colloidal system, the diameter of the particles lies in the range `10^(-7)` to `10^(-4)` cm. The size of the pore in the animal membrane is equivalent to the size of the partides present in a true solution, and so the particles in true solution can easily pass through the membranes. The particles of glue or gelatin are larger compared to the fine pores present in membrane. Hence, glue and gelatin cannot pass freely through it.