1a) Dialysis tubing can be used to make bags that model a cell with a semipermea

Question

1a) Dialysis tubing can be used to make bags that model a cell with a semipermeable membrane. These membranes are impermeable to sucrose but not water. Four bags were filled with the following solute concentrations: Bag A – 10 ml of 1% sucrose Bag B – 10 ml of 20% sucrose Bag C – 10 ml of 45% sucrose Bag D – 10 ml of 80% sucrose Each bag was weighed before placing them in a beaker: Bags B and C were placed in a beaker containing 80% sucrose Bags A and D were placed in a beaker containing 1% sucrose At 15 minute intervals, each bag was blotted dry, weighed, and returned to the same beaker. Q.) After 1 hour – did the weight of each bag change from the initial weight and if it did, how did it change, and why? Be sure to include the terms isotonic, hypotonic, and hypertonic.

Explanation / Answer

Water moves from high water potential to low water potential.

Water potential of a solution decreases with the increasing concentration of the solute.

i.e. A 10% solution contains high water potential than 1 20% solution.

In the given case,

A = 1% sucrose; Placed in 1% sucrose solution. Both solutions are isotonic. So, no change in the weight.

B = 20% sucrose; Placed in 80% sucrose solution. The solution in the dialysis bag is hypotonic. So, water moves out of the bag. Hence weight decreases.

C = 45% sucrose; Placed in 80% sucrose solution. The solution in the dialysis bag is hypotonic. So, water moves out of the bag. Hence weight decreases.

D = 80% sucrose; Placed in 1% sucrose solution. The solution in the dialysis bag is hypertonic. So, water moves into the bag. Hence weight increases.

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