GCSE Biology (AQA)

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Gravitropism

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Homeostasis and Response Plant Hormones

Gravitropism

2:25 Control and Coordination in Plants
Spec 4.5.4.1
Previous Phototropism Next Gibberellins
  • Gravitropism is a response where shoots and roots grow in response to gravity using hormones.
  • Gravitropism and geotropism are synonymous terms.
  • The prefix "geo" in geotropism refers to the earth, indicating roots growing downwards towards the earth.
  • Gravitropism enables trees to grow upright, even on a hillside.
  • Roots are positively tropic, growing in the direction of gravitational force.
  • Gravity acts as a pulling force directed towards the earth's center.
  • The plant hormone auxin affects growth; in roots, it causes cells to grow slower on the side where it accumulates.
  • Auxin accumulates on the lower side of a sideways-growing root, inhibiting cell growth there and causing the root to bend downwards.
  • In shoots, which are negatively tropic, auxin causes cells on the lower side to elongate faster, making the shoot grow upwards against gravity.
  • The difference in auxin's effect on roots and shoots results in roots bending downwards and shoots bending upwards.

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