Here's why:

* Phototropism is the growth of a plant in response to a light stimulus. Plants will bend towards a light source.

* Auxin is a plant hormone that plays a crucial role in regulating plant growth and development.

* How it works: When light strikes one side of a plant stem, auxin accumulates on the shaded side. This higher concentration of auxin stimulates cell elongation on the shaded side, causing the stem to bend towards the light.

Let me know if you have more questions about plant hormones or phototropism!