Fact 1: Plants exhibit phototropism, or growing toward a light source.

Fact 2: Many light sources such as the sun and most artificial lights produce unpolarized light.

Given the two facts above, answer the question "What is called when plants grow toward the sun or an artificial light?" with the following options: 
- Exfoliation
 - Brownian motion
 - heat energy
 - phototropism
 - photovoltaic
 - autumn
 - peachleaf willow
 - mitosis


 

    phototropism     