Answer:

tropism

AnswerCrossword Clue
TROPISMResponse to a stimulus, biologically
TROPISMPlant tendency to grow toward light
TROPISMTurning towards the sun, e.g.
TROPISMPlant's movement
TROPISMTendency to turn, as a flower toward light.
TROPISMWhy plants turn to the sun