The movement of sunflower heads tracking the sun is an example of:

Heliotropism, also known as solar tracking, is a form of phototropism where plants orient their leaves or flowers in response to the direction of the sun. Young sunflowers exhibit heliotropism by tracking the sun across the sky.

• Nyctinasty is the sleep movement of leaves or petals in response to darkness.
• Seismonasty is movement in response to touch or vibration.
• Geotropism is response to gravity.