How Do Sunflowers Face The Sun?

Young sunflowers face the sun when it rises in the east and then track its motion in the sky throughout the day till it sets in the west in the evening. The process repeats the next day, as sunflowers return to their ‘starting’ position, i.e. facing east. Ancient Greeks knew about this phenomenon, and they called such plants Heliotropium, meaning “sun turn”. Today, we call this phenomenon heliotropism. So, how do sunflowers face the sun? Also, do all sunflowers face the sun?