Osmosis | Biology for GCSE/IGCSE - Year 11 PDF Download

Osmosis

• Every cell is enveloped by a cell membrane, which exhibits partial permeability.
• Water can traverse into and out of cells via a process known as osmosis.
• Osmosis refers to the movement of water molecules from a solution of lower solute concentration (thus higher water concentration) to one of higher solute concentration (and lower water concentration) across a partially permeable membrane.
• This movement entails water flowing down its concentration gradient.
• The partial permeability of the cell membrane implies that it permits the passage of small molecules, such as water, while impeding the movement of larger molecules, such as solute molecules.

Osmosis and the Partially Permeable Membrane

Osmosis is the process of water moving from an area of high water concentration to an area of low water concentration through a partially permeable membrane. This movement occurs without the input of energy.

• Definition: Osmosis is the spontaneous movement of water molecules through a partially permeable membrane from a region of high water concentration to a region of low water concentration.
• Importance: Osmosis is crucial for the balance of water in cells and organisms. It helps in maintaining cell turgidity and plays a role in processes like nutrient uptake in plants.
• Mechanism: Osmosis occurs due to the random movement of water molecules. The net flow of water happens from the side with lower solute concentration to the side with higher solute concentration until equilibrium is reached.
• Example: In plant cells, osmosis is responsible for the entry of water into the cell, creating turgor pressure that keeps the cell rigid and helps support the plant structure.