If you take a cell that was living in seawater and drop it into fresh water, what will most likely happen? Will the cell contract and shrivel? Or will the cell expand and perhaps even burst?

the cell will expand and perhaps burst

Explanation:

A cell living in a seawater will be hypertonic, that is, the cell will have higher salt content. When such cell is put in freshwater, it will absorb water from the freshwater which is hypotonic until both are isotonic and because the freshwater is much compared to the cell, the cell will continue to absorb water in a bid to be in equilibrium with the freshwater surrounding and may likely burst.