* A semi-permeable membrane: This is the most crucial component. It allows water molecules to pass through freely but restricts the passage of larger molecules like solutes. The cell membrane, composed of a phospholipid bilayer, acts as this semi-permeable barrier.
* A concentration gradient: This refers to the difference in the concentration of water molecules (or solute concentration) across the membrane. Water will move from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration) to try and equalize the concentration on both sides.
* Water molecules: Obviously, water is essential for osmosis to happen. The water molecules are the ones that move across the membrane.
While not strictly a structure, the presence of solutes is also important. The difference in solute concentration across the membrane drives the movement of water.
In summary:
Osmosis is the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration. This process requires a cell to have a semi-permeable membrane, a concentration gradient, and water molecules.
