Answer an unit of measurement.
For example: inch, hour, minutes, feet, meters.
I don't completely understand the question, but I am guessing that you are trying to finish the sentence. If so, the answer is "Diffusion continues until the concentration on both sides of the membrane is <u>equal</u>". The reason it's equal is because diffusion always travels high to low, to reach a point of equilibrium. The particles are trying to move so that water is the same inside and outside of the cell/membrane, and the solute is also equal on the inside and outside of the cell/membrane. If that doesn't make sense, just comment any questions you have and I will try my best to answer :)
