GCSE Biology (AQA)

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Defining Osmosis

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Cell Biology Transport in Cells

Defining Osmosis

2:43 Osmosis
Spec 4.1.3.2
Previous Exchange in Fish Next Comparing Water Concentrations
  • Solutes are particles that dissolve in a liquid to form a solution.
  • The concentration of water decreases as more solute is dissolved.
  • A diagram shows two solutions separated by a barrier, with water molecules represented by blue dots and salt by orange dots.
  • Examples of solutes include salt and sugar.
  • The left solution in the diagram is dilute (high water concentration, low solute concentration), while the right solution is concentrated (low water concentration, high solute concentration).
  • Osmosis is defined as the diffusion of water from a dilute solution to a concentrated solution across a partially permeable membrane, involving only water molecules.
  • A partially permeable membrane allows only small molecules like water to pass through, not larger molecules like salt.
  • In osmosis, there is a net movement of water molecules from an area of higher water concentration to an area of lower water concentration.
  • Osmosis is a passive process, requiring no energy, and is crucial for cellular function as cells need water to maintain the cytoplasm.
  • The cell membrane is also partially permeable, allowing water to move in and out depending on the external and internal water concentrations.
  • Water movement across the cell membrane via osmosis depends on the relative concentrations of water inside and outside the cell.

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