lesson
Particles spread through random motion
1 · Learn
Diffusion is the net movement of particles from a region of higher concentration to one of lower concentration because particles move randomly. Individual particles do not know which way is needed; the overall spread results from their movement.
Diffusion can help substances move into and out of cells. A larger concentration difference can increase the net rate, but the material, temperature and distance also matter. At equilibrium particles still move even though there is no net change in concentration.
2 · Worked example
In a model with more particles on the left, particles cross both ways. More initially cross left to right, so the concentrations become more similar.
3 · Your turn
At equilibrium, have all particles stopped moving?
Check your answer
No. They continue moving, but there is no overall net movement caused by a concentration difference.
4 · Apply your learning
Trace an animated or paper random-motion model and identify which parts represent particles and which assumptions simplify real cells.
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Check a calculation · Year 5 onward
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Powers, roots and trigonometry · Year 7 onward
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