Why do sunflowers turn toward the Sun?

Sunflowers exhibit a behaviour called heliotropism, where their stems grow in response to sunlight. During the day, young sunflowers track the Sun from east to west, a movement driven by hormonal changes in the stem that cause differential growth. This behaviour maximises light capture for photosynthesis. Once the plant matures and blooms, it usually faces east to warm quickly in the morning and attract pollinators.