Final answer:
Paper changes when it absorbs water due to the hydrogen bonding between water molecules and cellulose fibres in the paper, causing capillary action which makes the paper absorbent and leads it to change in structure.
Step-by-step explanation:
Paper changes significantly when it absorbs water because of the interaction between water molecules and the cellulose fibres that make up the paper. Cellulose consists of long chains of molecules that have many -OH groups. These -OH groups form hydrogen bonds with water molecules, causing the water to be drawn up into the fibres. This process, known as capillary action, allows the water to spread throughout the paper, making it absorbent. The property of cellulose forming strong but flexible fibres that do not dissolve in water makes it ideal for creating materials like paper and cotton towels. However, when cellulose in paper absorbs water, it can lead to changes in the paper's structure, which is why paper deforms or wrinkles when wet.