Raisins swell up when placed in water.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Condition of Raisins**: Raisins are dried fruits that have lost most of their water content. In their dry state, they have a low water concentration and a high concentration of solutes (like sugars).

2. **Placing Raisins in Water**: When raisins are placed in water, they are surrounded by a solution that has a higher concentration of water compared to the inside of the raisins.

3. **Concept of Osmosis**: Osmosis is the movement of water across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration. In this case, the water outside the raisins (hypotonic solution) has a lower concentration of solutes than the inside of the raisins.

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