lesson
Updated 6 days ago
If you open a bottle of perfume in the corner of a room, someone standing near the opposite doorway will smell it within seconds.
This spontaneous spreading happens because of diffusion, which is the net movement of particles from an area of higher concentration to an area of lower concentration.
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In 1855, German physiologist Adolf Fick formulated the physical laws of diffusion after studying how salt moves through water, showing that particles always spread outward along a concentration gradient.
Why do particles move this way without any pump or biological motor pushing them?
The Particle Mechanism
All particles in liquids and gases possess kinetic energy, causing them to move randomly in all directions and constantly collide with one another.
Because there are more particles in a crowded area, more particles happen to bounce away from it than bounce toward it, resulting in an overall downhill flow.
How does your body exploit this passive physical process to keep billions of living cells alive?
Gas Exchange in the Lungs
In human lungs, oxygen moves from tiny air sacs called alveoli directly into surrounding blood capillaries across a membrane that is only one cell thick.
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At the exact same time, carbon dioxide diffuses out of the blood and into the alveoli because its concentration is higher in the incoming deoxygenated blood than in inhaled air.