Answer:
The dialysis tubing is semi permeable in nature which means that it allows some molecules to pass through it while hinders the movement of other molecules.
Process:
A dialysis tube filled with water and sugar when placed in pure water will act as a setup that can depict the process of Osmosis. Sugar molecules will not be able to pass the membrane while pure water molecules will move from the area of higher concentration to the area of lower concentration (inside the dialysis tube). This is because the pure water is less concentrated while the water in dialysis tube contains more concentrated solution. This will also increase the liquid level in the dialysis tube.
For example: If we have a dialysis bag that is not permeable to sugar but is permeable to water and it is was placed in a beaker full of pure water.
Suppose the bag’s initial weight was 15g but after 15 minutes the bag's weight can change upto 17 grams, why it happened is due to process of osmosis of movement of pure water into the dialysis bag.
Hope it helps!