The reason for the different behavior lies in the presence or absence of a cell wall. Both plant and animal cells take in water by osmosis when placed in fresh water. Animal cells lack a cell wall. As water enters, the cell swells and the cell membrane cannot withstand the increasing internal pressure, causing the cell to burst (lyse*). Plant cells have a rigid cell wall outside their cell membrane. This strong wall prevents the cell from bursting as water enters and the cell swells. Instead, the cell becomes turgid*, with the cell membrane pushing against the cell wall.