GCSE Biology (AQA)

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Defining Diffusion

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Cell Biology Transport in Cells

Defining Diffusion

2:39 Factors Affecting Diffusion
Spec 4.1.3.1
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  • Diffusion is the spreading out of particles of a gas or any substance in solution.
  • Example given: Pouring chlorine into a swimming pool results in a high concentration at the point of entry and a lower concentration further away.
  • Diffusion causes a net movement of a substance from an area of higher concentration to an area of lower concentration.
  • Particles move randomly but show a net movement from high to low concentration areas.
  • Particles continue moving even after the animation stops, simulating continuous diffusion in real life.
  • The difference in concentration between two areas is termed the concentration gradient.
  • Particles move down or with their concentration gradient.
  • When concentration is the same on both sides, there is no net movement, and particles reach equilibrium.
  • Diffusion into and out of cells is a passive process, requiring no energy.
  • Substances like oxygen, carbon dioxide, and urea move across cell membranes by diffusion.
  • The cell membrane is partially permeable, allowing selective movement of substances in and out of cells.

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