How can some large molecules and charged ions get through the cell membrane?

water to move into the cell.

Explanation:

Osmosis is the process by which water moves from a region of low solute concentration (high water conc.) to a region of high solute concentration (low water conc.) across a semipermeable membrane. The movement of water is initiated by the formation of an osmotic gradient i.e. difference in concentration between the two sides of the membrane.

In this case, an animal cell is said to be surrounded by fresh water. This means that the solution in the animal cell is HYPERTONIC (high in solute concentration) to the solution in the extracellular environment, which is HYPOTONIC. This osmotic pressure causes water to move into the animal cell i.e. from the region of high water conc. (freshwater) into region of low water conc. (animal cell), causing the cell to burst.