* Osmosis: Osmosis is the movement of water across a semipermeable membrane (like the cell membrane) from an area of high water concentration to an area of low water concentration.

* Animal Cells and Fresh Water: Animal cells have a higher concentration of solutes (dissolved substances) than fresh water. This means there is a lower concentration of water inside the cell compared to the surrounding environment.

* Osmotic Pressure: Due to this difference in concentration, water will move from the outside (where it's more concentrated) into the cell (where it's less concentrated) to try to equalize the concentration. This movement of water into the cell creates pressure called osmotic pressure.

* Bursting: If the osmotic pressure is too high, the cell membrane can't withstand the pressure, causing the cell to swell and potentially burst (a process called lysis).

In summary: The freshwater environment creates a situation where water rushes into the animal cell, causing it to swell and potentially burst due to the imbalance in osmotic pressure.