Sunflowers in the bud stage exhibit Heliotropism. At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they follow the sun from east to west, while at night they return to an Eastward orientation. Sunflowers in their blooming stage lose their heliotropic capacity. The stem becomes "frozen", typically in an eastward orientation. The stem and leaves lose their green color.
Sunflower heads sold as snacks in China. Sunflower oil, extracted from the seeds, is used for cooking, as a carrier oil and to produce margarine and biodiesel, as it is cheaper than olive oil. A range of sunflower varieties exist with differing fatty acid compositions; some 'high oleic' types contain a higher level of healthy monounsaturated fats in their oil than even olive oil. Sunflowers may also be used to Extract toxic ingredients from soil, such as lead, arsenic and uranium. They were used to remove uranium, cesium-137, and strontium-90 from soil after the Chernobyl disaster.
