Photo means light. The process when an organism, especially plants, gives a directional response in the presence of light is called phototropism.
Auxins:
Auxins are the phytohormones found in plants, mainly in stem tips and root tips.
It stimulates the formation of chloroplasts.
It also promotes the division of cells.
Auxins are responsible for cell elongation in protoplasm.
Auxins move to the darker side of the plant (or the one not receiving light) which leads to their growth. This creates a bending effect whereby the lighter side directionally faces the lighter side.
