Explain the role of auxins in the control of phototropism

A phototropism is the growth of a plant in response to light. This is mediated by auxins such as IAA (Indoleacetic acid). This is released in the tips and shoots of flowering plants. In response to light IAA moves to the shaded side in both shoots and roots. In shoots this causes the shaded side to elongate and therefore the shoot bends towards the light. In roots this inhibits root growth on the shaded side and therefore the root bends away from the light.