2.82: Describe Positive Phototropism of Stems

PHOTOTROPIC RESPONSE: Growth in Response to the Direction of Light

AUXINS: Plant Hormone Produced in the Stem Tips and Roots, which Controls the Direction of Growth

• Auxin is Produced at the Tip of Stems and Roots and Changes the Elasticity of Cells (More Elastic will Absorb More Water and therefore Grow Longer, Causing Bending in the Stem or Root)
• Factors such as Gravity can Interfere the Transport of Auxin Causing it to be Unevenly Distributed, Causing a Phototropic Response

POSITIVE PHOTOTROPISM OF PLANTS:

POSITIVE PHOTOTROPISM IN STEMS

Diagram showing Positive Phototropism Caused by Auxins in the Stems

PROCESS: Auxins will be Produced at the Tip of the Stem As the Unshaded Side of the Stem is Exposed to the Light, Light will Destroy Auxins on the Unshaded Side The Shaded Side will still have Auxins as it is Not Exposed to Light and Auxins will Stimulate the Growth of Stem Cells so will cause Cells on the Shaded Side to Grow Longer and Elongate The Stem will Bend Towards the Light, Allowing Positive Phototropism to Absorb More Light for Photosynthesis