A hypotonic solution has a low solute concentration than the inside of the cells (solute concentration in the cell is high). Osmotic forces then cause water from a solution to enter the cells. The cell eventually stretches and bursts in the process becoming lysis.
(This is my best explanation, I'm not sure if you need what would happen if the cell was placed in specifically 80%, btw this is the social studies thread, not the biology one!!)
Hope this helps :0