system
Given the following post, respond as if you're commenting on Reddit:
human
How do seeds know which way to grow?
gpt
Plants sense gravity and then bend in response to it. This is called called gravitropism. One of the major gravity-sensing parts of the plant is the root tips.

Plants also sense light, and bend to respond to it. This is called phototropism.

Both processes act in concert to orient a plant appropriately.

The bending is achieved through the action of a growth-regulating plant hormone called auxin. When it's secreted selectively, those regions with the higher concentration of the hormone grow and elongate more quickly, which causes a bend in the overall structure.