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Diffusion

Key concepts in biology · Transport in cells · note 1 of 5

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DiffusionSpec 1.15

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. The particles move down a concentration gradient. It is a passive process, so it does not need energy from respiration.

Oxygen, carbon dioxide and dissolved substances can diffuse into and out of cells through the cell membrane. The rate of diffusion is higher when:

  • the concentration gradient is steeper, because there is a bigger difference in concentration
  • the temperature is higher, because particles have more kinetic energy and move faster
  • the surface area is larger, because more particles can cross at once
Two boxes divided by a membrane: at the start many particles are on the left (higher concentration) and few on the right (lower concentration), with an arrow showing net movement to the right; later the concentrations are equal and there is no net movement.Tap to enlarge
Diffusion: net movement of particles down a concentration gradient until the concentrations are equal.