BRAINCAKEDiffusion
Diffusion is the net movement of particles (molecules or ions) from a region of higher concentration to a region of lower concentration, down a concentration gradient.
Particles in liquids and gases move randomly because of their kinetic energy. More particles move from the concentrated region to the dilute region than the other way, so there is a net movement down the gradient. Diffusion is passive: the cell uses no ATP.
When the concentrations become equal, particles still move but in equal numbers in both directions, so there is no net movement. This is equilibrium.
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Key terms in this lesson
- concentration gradient
- The difference in the concentration of a substance between two regions, which determines the direction of net diffusion.
More in Cell Transport Mechanisms
- The Need for Transport
- Transport Across the Cell Membrane
- Passive and Active Transport
- Facilitated Diffusion
- Water Potential ψ
- Osmosis
- Modelling Osmosis
- Osmotic Concentrations
All 18 lessons in Cell Transport Mechanisms · All Edexcel AS-level Biology topics