To answer this question, you need to understand the concepts of hypertonic, hypotonic, and semipermeable membrane.
Hypertonic refers to a solution with a higher concentration of solutes (in this case, sugar molecules) compared to another solution. Hypotonic refers to a solution with a lower concentration of solutes compared to another solution. A semipermeable membrane is a membrane that allows the passage of certain substances while blocking others.
In this experiment, the dialysis tubing acts as a semipermeable membrane. It allows water molecules to pass through but blocks the movement of sugar molecules.
When the tubing is initially set up with water inside and immersed in the sugar solution, the sugar solution is hypertonic compared to the water inside the tubing. This means that the concentration of sugar molecules is higher outside the tubing than inside.
Since the tubing is permeable to water molecules but impermeable to sugar molecules, water molecules will tend to move from the area of lower solute concentration (inside the tubing) to the area of higher solute concentration (outside the tubing). This movement of water is called osmosis.
As a result, after 24 hours, some of the water molecules inside the tubing will move outwards into the sugar solution through osmosis. This movement of water causes a decrease in the volume of water inside the tubing, leading to the observed change in the size of the dialysis tube (in this case, the tube shrinks).
In summary, the change in the size of the dialysis tube after 24 hours is due to osmosis, with water molecules moving from an area of lower solute concentration (inside the tubing) to an area of higher solute concentration (outside the tubing) through the semipermeable membrane.