Phototropism is the growth of an organism which responds to a light stimulus. This involves growth toward a light source. In this pic, these palms are crowded by other trees and are growing towards the area of the most sunlight. How does this work? Plants first sense the light with photoreceptors, which are molecules consisting of protein and pigment that absorbs light. When the light is absorbed, the protein changes shape, initiating a signaling pathway. Plants contain a hormone called auxin, which coordinates growth and behavioral processes throughout life cycles. Auxin is responsible for the curvature of the stems allowing the plants to grow in a given direction.