Phototropism, the stem grows towards light as the sunlight causes auxins to be produced in the shoot tips which move to the side away from the light and causes elongation on the shaded side to grow towards the light source.
How does the roots of a plant respond to light?
negative phototropism, auxins are produced and move to the shaded side of the roots but in high concentrations in the root they inhibit growth and cause the unshaded sight to elongate more and the root bends away from the light source.
How are auxins used as a weed killer?
a version of auxins allow for it to be taken up in plants but not naturally diffuse out which leads to auxins building up in cells and causing rapid cell elongation which causes the stem to grow too quickly and collapse. Also using up all the plants resources which will be its end.
