What does the net change in the potato sample indicate?

The net change in the potato sample indicate osmosis process.

Explanation:

In osmosis process the solvent molecules move from low solute concentration to high solute concentration. potatoes are full of water and starch, and will gain water when immersed in watery solutions. Conversely looses water in concentric solutions.

For example cut a potato in to two halves, put one half in salt water and the other in normal water. After half an hour remove both the first will have shrunk, indicating that water is diffusing from a less concentrated solution to a more concentrated solution. The one in the tap water solution, in contrast, will actually swell slightly, indicating that it is taking in water.

Since potatoes already contain sugar, less water will diffuse out of the potato placed in sugar water.