The movement of plant components in reaction to light is known as phototropism. Shoots are phototropic in a positive way, whereas roots are phototropic in a negative way. The action of auxins like indole-acetic acid causes phototropism in plants (IAA). IAA molecules travel to the opposite (shaded) side of the shoot when one side is exposed to sunlight. IAA causes cell division and elongation on the shaded side of the shoot rather than the light-exposed side. This results in unequal growth on both sides of the stalk, with the shaded side growing faster than the sunny side. As a result, the shoot bends toward the light.