The correct option is this: WATER MOVES INTO THE CELL, CAUSING IT TO BURST.
Osmosis is the process by which water molecules move through a semi permeable membrane from the region of low solute concentration to the region of higher solute concentration. In the question given above, the solute concentration inside the unicellular organism is higher, therefore water from the tank, which has a lower solute level will move into the cell of the organism, causing the cell to burst.