Question

a student wants to model the net movement of water out of a cell using a semi - permeable bag, water, a large beaker, and salt. which setup could he use to model the net movement of water out of a cell?
a place a bag containing a 30% salt solution into a beaker containing a 10% salt solution
b place a bag containing a 30% salt solution into a beaker containing a 20% salt solution
c place a bag containing a 10% salt solution into a beaker containing a 10% salt solution
d place a bag containing a 20% salt solution into a beaker containing a 40% salt solution

Explanation:

To model water moving out of a cell (represented by the semi - permeable bag), the water potential inside the bag (cell) should be higher than outside (beaker). Water potential is inversely related to solute (salt) concentration. So the salt concentration inside the bag should be lower than in the beaker.

• Option A: Bag has 30% salt, beaker has 10% salt. Water would move into the bag (high to low water potential, but bag has higher solute, lower water potential? Wait, no: solute concentration in bag (30%) > beaker (10%), so water potential in bag < beaker. So water moves into bag. Not correct.
• Option B: Bag has 30% salt, beaker has 20% salt. Solute in bag > beaker, water potential in bag < beaker. Water moves into bag. Incorrect.
• Option C: Bag has 10% salt, beaker has 10% salt. Equal solute, equal water potential. No net movement. Incorrect.
• Option D: Bag has 20% salt, beaker has 40% salt. Solute in bag (20%) < beaker (40%), so water potential in bag > beaker. Water moves from bag (higher water potential) to beaker (lower water potential), which is water moving out of the "cell" (bag). Correct.

Answer:

D. Place a bag containing a 20% salt solution into a beaker containing a 40% salt solution