Summary
Highlights
Osmosis is the movement of water molecules from a high water potential area to a low water potential area through a semi-permeable membrane. Water potential, represented by a trident symbol, measures the potential of water to move. Pure water has the highest water potential, valued at zero, and all other solutions have negative water potentials. A more negative value indicates a more concentrated solution with less water.
When cells are placed in a dilute solution or pure water (high water potential), water moves into the cell by osmosis. In animal cells, this causes them to swell and eventually burst because the cell membrane cannot withstand the increased volume. It's crucial to state that water moves by osmosis from high to low water potential.
In an isotonic solution, the water potential of the solution is the same as the cell's cytoplasm. This means there is no net movement of water into or out of the cell, as equilibrium is reached. While water molecules still move, the rates of movement in and out are equal.
When cells are in a concentrated solution (low water potential), water moves out of the cells by osmosis. Animal cells will shrivel and shrink because they lose water and volume from their cytoplasm, lacking a cell wall for structural support.
Similar to diffusion, the rate of osmosis is affected by the water potential gradient, membrane thickness, surface area, and the amount of aquaporins. A higher water potential gradient, thinner membrane, larger surface area, and more aquaporins all lead to a faster rate of osmosis.