Shoots of a plant bends towards the light because
Unequal distribution of auxins
Unequal distribution of auxin causes bending of shoots towards sunlight. Auxin is a hormone synthesized by meristematic cells at shoot tip. It moves from shoot tip to other parts and tends to get accumulated more on the darher side of the plant. This results in the shady side of stem grows faster than the side receiving light and becoes heavy. As a result, stem bends towards the direction of light.