Should there be an increase or decrease in mass of the dialysis tubing (with glucose, starch in it) after 30mins soaked in distilled water?

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pacorz | High School Teacher | (Level 3) Educator

Posted on

The dialysis tubing in this experiment is a model for a cell. Like cells, it is filled mostly with water with some other things dissolved in it (this represents the cytoplasm), and is surrounded by a semipermeable membrane which simulates the cell membrane.

Because there are substances dissolved in the water inside the tubing, there is less water (by percent) in the tube than in its surroundings, which are basically pure water, and are hypotonic to the contents of the tubing. The process of osmosis causes water to move preferentially from areas where there is more water to areas where there is less. In this case water will move from the surroundings into the tubing, and you will find that this model cell will become more full and will weight more, because water has moved into it.

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apushstudent | Student, Grade 10 | (Level 3) eNoter

Posted on

Looks like an AP lab.  The Bio test was today so this may not be helpful.  Since there is starch and glucose in the dialysis bag, the concentration of water is lower in the bag than in the distilled water.  water always moves down its concentration gradient by osmosis.  Water will move into the bag down its concentration gradient, resulting in an increase of mass.

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