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Biology LibreTexts

Exercise 3: Osmosis Across a Membrane

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  • Osmosis Across a Membrane

    Observe the movement of water across a semipermeable membrane.


    • Dialysis bags (4 per group)

    • Dental floss

    • 15% sucrose solution

    • 30% sucrose solution

    • Triple beam balance

    • Beakers (4 per bench)

    • Graduated cylinder

    • Stir rods


    1. Obtain 4 strips of dialysis tubing and tie a knot in one end of each using the dental floss.
    2. Pour approximately 10ml of each solution into separate bags (see table below).

      Tube 1 Tube 2 Tube 3 Tube 4
    Inside bag        
    Inside beaker        
    Tonicity of bag?        
    Predicted outcome?        
    1. Remove most of the air from the bag (but leave a little bit of space) and tie the bag.

    2. Blot the bags to remove any sugar that may have spilled; check the bags for leaks.

    3. Record the weight of each baggie in the data table.

    4. Place a bag in each beaker (be sure to keep track of which bag is in which beaker!). Fill the beakers with enough of the appropriate solution to cover your bags (refer to the above table).

    5. Predict what you think will happen during the experiment.

    6. Record weight every 10 minutes in data table.

    7. After 30 minutes, remove the bags from solution and record the final weight.

    Data Tube 1 Tube 2 Tube 3 Tube 4
    Weight at 0 min        
    Weight at 10 min        
    Weight at 20 min        
    Weight at 30 min        


    1. Did you results match your predictions? Propose an explanation for why your results (either overall or an individual bag) may have differed from what you were expecting.

    2. Based on what you have observed, are the dialysis bags permeable to sucrose?