geotropism:
The growth of a living organism in response to gravity, as the downward growth of plant roots.

phototropism:
Growth or movement of a sessile organism toward or away from a source of light.

Thigmotropism:
The turning or bending response of an organism upon direct contact with a solid surface or object. Also called stereotropism.

Cemotropism:
Movement or growth of an organism or part of an organism in response to a chemical stimulus.

Tropism