Isotonic..Hypotonic..Hypertoni…

My students used to have trouble with this also so here's how I explained it. We all know that water follows salt so that is the solute I used for my example. The solute could be any electrolyte, I just like to use salt. So in an isotonic solution, iso- as a prefix means 'same'. So the salt inside and outside the cell is the same, so no water movement and no reaction by the cell. Hypotonic, hypo- is the prefix for 'below'. So the salt in the solution is lower than in the cell, so the water from the solution will enter the cell (remember water follows salt) so the cell will start to swell and maybe even burst (lyse). In hypertonic, hyper is the prefix for "above", so in this case the salt solution is higher than in the cell, so the water in the cell moves out into the solution causing the cell to shrink in size (crenate). I hope that helps.