Just like humans, plants also have internal biological clocks, referred to as a circadian rhythm. The circadian rhythm of a human being creates several physiological and chemical changes within the body. Similarly, the circadian rhythm of a plant allows it to respond to changes in roughly 24 hour cycles. So how does the sunflower circadian rhythm play a role in sun tracking behavior? Before the break of dawn, a young sunflower faces east, towards the direction of the sunrise. As the sun moves from East to West, the flower turns westward as well. When the sun sets, the flower reverts to its original position, facing East to begin the cycle again the next day. According an article published in the journal Science in 2016, researchers believe that sunflowers demonstrate this type of Heliotropism due to their stems elongating at different rates at different times of day. This is what researchers observed during their study. When the sun starts moving from East to West in the sky, the east side of the stem of a sunflower plant grows more rapidly than the West side. Due to this unequal growth on either side, the flower tends to bend in the direction of the sun. Similarly when the sun finally sets, the growth on the West side of the stem is greater than the growth on the East. As a result of this, the stem bends east, that is, in the direction where the sun would rise again the next morning.