Diffusion
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
Diffusion is the passive movement of a substance from higher to lower concentration until the concentration is equal throughout a space.
Show
Ammonia vapor released from a bottle spreads outward through a room, thinning as it moves from its point of highest concentration.
Watch for
Diffusion needs no cellular energy — the concentration gradient itself, not the cell, drives the movement.