The process of phototropism is the growth of an entity in response to a light stimulus. This process is most commonly observed in plants but can also occur in other entities such as fungi. Plant cells that are farthest from light have a chemical known as auxin which is active and reacts when phototropism occurs. Tips of leaves and stems contain auxin, causing them to positively grow towards the light.
- In this phenomena, the plant grows towards the sunlight hence the plant body grows in this process. When the plant body grows in the opposite direction to the sunlight, it is termed negative phototropism.
- Positive phototropism is the response of a plant toward a light source, while negative phototropism causes growth in the opposite direction.
- Plant roots usually use negative phototropism although additionally, they use gravitropism, which is the response to gravitational pull.
An example of a plant that is highly phototrophic is the sunflower. Scientists have discovered that sunflowers need more light for growth and survival, as well as fruiting, and flowering, than most other flowering plants. They can be visibly seen to track the sun’s movements from East to West throughout the day. At night, the heads move back from West to East in anticipation of the next day’s sunrise.