Cell membranes are completely permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.
Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell’s cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell’s cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute as an another solution (e.g. the cell’s cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.