Compare and contrast penetrating solutes and non-penetrating solutes.

Different solutions occupy different compartments that are separated by membranes.

For example, the composition of the intracellular fluid (fluid inside a cell) is different from that of the extracellular fluid (fluid outside the cell). Both liquids are separated from each other by the cell membrane.
Same with dialysis: the solutions inside and outside the dialysis tubing are different and they are separated from each other by the dialysis membrane.

"Penetrating and non penetrating" refers to the ability of these solute particles to cross (go through) the membranes separating the solutions.

Penetrating solutes: solutes that can pass through a membrane.

Non-penetrating solutes: solutes that cannot pass through a membrane.

HOWEVER, BE CAREFUL BECAUSE.......

Solutes whose diffusion inside is as fast as their active transport to the outside behave like non-penetrating solutes.

AND

Solutes which are disposed of by the cell as fast as they diffuse inside behave also like non-penetrating solutes.