1) Tropism 
Heliotropism, a form of tropism, is the diurnal motion or seasonal motion of plant parts (flowers or leaves) in response to the direction of the sun. The habit of some plants to move in the direction of the sun was already known by the Ancient Greeks. They named one of those plants after that property Heliotropium, meaning sun turn. The Greeks ass...
movement of plants towards sunlight
• (n.) The phenomenon of turning toward the light, seen in many leaves and flowers.
He`li·ot'ro·pism noun [ Helio- + Greek ... to turn.] (Botany) The phenomenon of turning toward the light, seen in many leaves and flowers. 
The characteristic of turning toward the light.
Type: Term Pronunciation: hē′lē-ot′rō-pizm Synonyms: heliotaxis
[n] - an orienting response to the sun
heliotropism 1. Plant movement or orientation in response to the location of sun light. 2. The reversible phenomenon of color change in a solid as the result of exposure to sun light.
noun an orienting response to the sun