The directed movement of a living organism or cell toward or away from a chemical stimulus in its surroundings.
From Greek chemo- 'chemical' + taxis 'arrangement, movement in order.' The term was coined in the late 1800s as scientists observed bacteria moving toward nutrients and away from toxins.
This is why bacteria swarm toward sugar and mosquitoes find you in the dark—life has evolved molecular compasses that read invisible chemical maps written in the environment.
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