2.85: Understand the Role of Auxin in the Phototropic Response of Stems

PHOTOTROPIC RESPONSE: Growth in response to the direction of light

AUXINS: Plant hormone produced in the tip of stem and roots which controls the direction of growth

• Auxin changes the elasticity of cells to alter the growth of cells, therefore changing the direction of growth (increase in elasticity will allow cell to absorb more Water, causing size of cell to increase and bend towards specific direction)
• Factors including light and gravity can alter the distribution of Auxin within stem and root, causing different responses

PHOTOTROPIC RESPONSE OF STEMS:

POSITIVE PHOTOTROPISM

Diagram showing Positive Phototropism in Stems

PROCESS: During growth, Auxin produced at tip will be redistributed by light receptors to the shaded side of the Stem As Auxins promote growth of Stem cells, cells on the shaded side will grow larger and elongate (increase in elasticity allows cell to absorb more Water to grow larger in size), whilst cells on the unshaded side exposed to light will grow at a slower rate As a result, Stem will grow towards the direction of light - Positive Phototropism, allowing Plant to maximise the absorption of light for Photosynthesis