GCSE Biology (AQA)

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Phototropism

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Homeostasis and Response Plant Hormones

Phototropism

1:45 Control and Coordination in Plants
Spec 4.5.4.1
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  • Phototropism is a response where plant shoots and roots grow towards or away from light, influenced by hormones.
  • The term "phototropism" originates from the Greek words "photo" (light) and "tropism" (turning).
  • Diagrams illustrate how plant stems bend towards sunlight.
  • Plant stems that grow towards light are described as positively phototropic.
  • When exposed to light, a hormone called "aen" accumulates on the shaded side of the shoot, promoting growth towards the light.
  • Cells in plant stems elongate faster on the shaded side, causing the shoot to bend upwards towards the light.
  • Plant roots that grow away from light are negatively phototropic.
  • In roots, the hormone "Orin" accumulates on the shaded side when exposed to light, but unlike in shoots, Orin inhibits cell elongation.
  • This inhibition of growth on the shaded side of roots causes them to bend downwards, further into the ground.

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