What happens to cells in a hypotonic solution?

When cells are placed in a hypotonic solution, the concentration of solutes outside the cell is lower than that inside the cell. Due to osmotic pressure, water will move into the cell in an attempt to equalize the solute concentrations on both sides of the cell membrane. As water enters, the cells will begin to swell. If the influx of water is significant enough, it can lead to the cell bursting, or undergoing lysis. This phenomenon occurs because animal cells, in particular, lack a rigid cell wall that would otherwise help to counteract the effects of excess water. In summary, in a hypotonic environment, cells will swell as they take in water to balance solute concentrations.