Is a sunflower heliotropic and why?

Yes, sunflowers are heliotropic, meaning they turn their heads to follow the sun's movement across the sky. This behavior is particularly evident in their early growth stages, helping them maximize light exposure for photosynthesis. The phenomenon is driven by differential growth on the sides of the stem, which causes the flower to tilt towards the sunlight. However, once sunflowers mature and their flowers bloom, they generally face east and remain fixed in that position.