Phototropism in a plant stem or shoot – The bending of a plant stem towards light represents the phototropism process. Due to the action of auxin, a growth hormone, the plants stem bends towards the light. This hormone is present at shoot tip of the growing plant. It usually prefers to stay in shade or away from sunlight so when the sunlight falls on the stem directly from one side then it gets concentrated on the other side. Due to presence of more auxin, the shady side of the stem or shoot grows longer in comparison to the side of stem which is facing direct sunlight hence, makes the stem bend towards light.