Phototropism

n.	1.	(Plant Physiol.) The tendency of growing plant organs to move or curve under the influence of light. In ordinary use the term is practically synonymous with heliotropism.
	2.	(Microbiology) exhibiting movement in a direction toward (positive phototropism) or away from (negative phototropism) a source of light.

Noun

1.

phototropism - an orienting response to light

tropism