One important light response in plants is phototropism, which involves growth toward—or away from—a light source. Positive phototropism is growth towards a light source; negative phototropism is growth away from light.

Is tropism a response?

Tropism, response or orientation of a plant or certain lower animals to a stimulus that acts with greater intensity from one direction than another. It may be achieved by active movement or by structural alteration.

How does the phototropic response occur?

The phototropic response occurs because greater quantities of auxin are distributed to the side away from the light than to the side toward it, causing the shaded side to elongate more strongly and thus curve the stem… ... stems toward the light (phototropism) and against the force of gravity (geotropism).