Osmosis

Osmosis is the movement of water molecules from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).
Like diffusion, osmosis is a passive process and does not require the input of energy from the cell.
It takes place across a semi-permeable membrane that allows the passage of water molecules while blocking the passage of solute particles.
Osmosis only takes place if there’s a difference in solute concentrations, which we call a concentration gradient.
It continues until the concentrations of water on both sides of the membrane are equal, or until the system reaches equilibrium.

Osmosis is essential for many biological processes and all living cells rely on it to some extent.
It plays a key role in the transport of nutrients and waste materials in and out of cells.
It is critical for maintaining a cell’s turgidity or firmness. In plant cells, osmotic pressure helps to maintain the structure of the cell, making the plant stand upright.
Osmosis also aids in the regulation of hydration and homeostasis within cells and across whole organisms.
It is important for water uptake in plant roots, as well as in the reabsorption of water in the human kidney.

A hypertonic solution has a higher solute concentration (and therefore, a lower water concentration) than inside the cell. If a cell is placed in a hypertonic solution, water will move out of the cell via osmosis, causing the cell to shrink.
A hypotonic solution has a lower solute concentration (and therefore, a higher water concentration) than inside the cell. If a cell is placed in a hypotonic solution, water will move into the cell via osmosis, causing the cell to swell and possibly burst.
An isotonic solution has the same solute and water concentration as inside the cell. In an isotonic solution, there is no net movement of water in or out of the cell, so the cell retains its original size.