Final answer:
After a few days of a dahlia stem being toppled onto the ground, you would likely notice that the stem grows upward due to the plant's negative gravitropism, guided by the settling of amyloplasts and distribution of the growth hormone auxin.
Step-by-step explanation:
Gravitropism is the growth of plants in response to the pull of gravity. Negative gravitropism describes the upward growth of plant shoots, while positive gravitropism refers to the downward growth of roots. When a dahlia stem is toppled by the wind and lies on the ground, after a few days, you would likely notice that the stem grows upward. This upward growth, despite the plant being on its side, is due to the plant's gravitropic response, ensuring that the shoots grow towards the light and away from the pull of gravity. This is made possible by amyloplasts, which settle to the bottom of the gravity-sensing cells within the plant and influence the distribution of auxin, a plant growth hormone that stimulates cells on the lower side of the shoot to expand, causing the shoot to curve upward.