A piece of dialysis tubing is filled with a solution of 60 % glucose and placed in distilled water. Osmosis will cause water to move how?

Answer 1

Hey! Good question.

The first thing to consider here is that all living things are in a constant state of trying to achieve equilibrium, or balance. Cells are constantly trying to make things even with their surroundings. The dialysis bag acts as a model for a cell.

Now we can consider the situation... you have a bag, or cell model, with 60% glucose inside. Glucose is a sugar, and sugar molecules are HUGE. On the outside, you have 100% water. Water molecules are small and they can move pretty much anywhere they want. This cell/dialysis bag is not in a state of equilibrium, because the inside contents do not equal the outside contents. So how does the cell try to fix that?

Think of the dialysis bag as a gate at the amusement park... the kind with the turn-styles. It is a selectively permeable membrane—selective meaning “some stuff” and permeable meaning “able to pass”. The dialysis bag acts just like a living cell does, as living cells are also selectively permeable.

How is it selectively permeable? There are a few ways, but a lot of it is based on size.

Think about how small those turn-styles are at the amusement park. You could probably get a dog through one of those. But there is NO WAY you’d get a rhino through one of those. The inside of the dialysis bag is made of 60% glucose molecules (rhinos— cause glucose is huge) and 40% water (dogs—much more reasonable size), so a ratio of 60 glucose molecules for every 40 water molecules. The outside is 100% water (dogs)... so a ratio of 0 glucose rhinos to 100 water dogs. The cell wants equal ratios of rhinos to dogs on the inside of the cell versus the outside.

But remember... the glucose rhinos can’t pass the selectively permeable membrane of turn styles, because they’re too big!! They’re stuck inside. Only water dogs can pass. So the cell tries to move towards equilibrium by flooding water dogs in through the membrane to the inside of the cell, diluting the glucose rhinos and getting that ratio as close to the 0:100 ratio on the outside as possible.

Hope this helped!