According to the Infoplease website from Pearson Education, the biological importance of osmosis is that it facilitates the distribution of essential nutrients in the body and the excretion of metabolic waste products. Cells have semipermeable membranes, and osmosis makes it possible for liquid solvents to pass through these cell membranes.
Infoplease notes that cells of plants and animals have outer coverings called cell membranes, which serve as a barrier that separates the cells from their environment. This semipermeable membrane controls the substances that enter and leave the cell. This means that not all substances can enter the cell with equal ease. Without this selective mechanism, all the essential substances spread into the surroundings of the cell, and even toxic substances are able to invade the cell.
Infoplease states that through the process of osmosis, liquid solvents that the body needs are able to pass through semipermeable membranes that do not allow solutes to enter. If a cell is exposed to an isotonic solution, it neither swells nor shrinks. If a cell is placed in contact with a hypertonic solution, the cell decreases in size because it loses water. Lastly, if it is exposed to a hypotonic solution, the cell enlarges.