Cells in isotonic solution stay the same because the solutes on either side of the membrane are even. In hypertonic solution the cells actually crenate, or in other words, they will shrivel because the solutes on the inside are less than the outside. They rush in and burst the membrane. Hypotonic solutions are just the opposite. The solutions on the inside are greater than on the outside, which causes everything to rush into the cell and it lyses.
