Question

[ TIMED!!!! ] Dialysis is an important biochemical procedure that removes salt from protein preparations. This diagram shows the scheme of an experiment of dialysis.

A semi-permeable bag containing 100 mM NaCl, 100 mM sucrose and 50 mg/ml protein is put into a tank of water (shown on the left). The bag only allows H2O and small inorganic ions, but not sucrose and protein, to pass through. After diffusion has come to an equilibrium (shown on the right side), the volume of solution in the bag is 120% of the original volume.

How does the water potential, the concentration of sucrose, and the solution pressure inside the bag change over time?

( Pic 1 is the reference, pics 2-5 are the options )

Answer 1

The water potential inside the bag will initially be higher than the water potential outside the bag, due to the presence of the protein and sucrose molecules.

The scenario above cause water to flow into the bag by osmosis. As the volume of the solution in the bag increases, the water potential will decrease. Eventually, the water potential inside the bag will reach equilibrium with the water potential outside the bag, and no further osmosis will occur.

The concentration of sucrose inside the bag will remain constant over time, since sucrose molecules are too large to pass through the semi-permeable membrane.

The solution pressure inside the bag will increase over time, due to the increase in volume. Solution pressure is the pressure that a solution exerts on the walls of its container and is caused by the bombardment of the container walls by the solute molecules.