The young sunflower plant would move its stem and flowering head in the direction of the sun as it moves across the sky from sunrise to sunset, a phenomenon known as heliotropism. In the morning, the plant would face east towards the rising sun, and then gradually turn westwards throughout the day to face the setting sun. During the night, the plant would reset its direction towards the east in anticipation of the next sunrise. This movement is guided by the hormone auxin, which accumulates on the shaded side of the stem and causes elongation of cells on that side, resulting in curvature towards the light.
