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A-Level Biology OCR A

Shoots Roots  Cell Elongation Lower Inhibits Promotes In 

Shoots are negatively geotropic (grow upwards), and roots are positively geotropic (grow downwards), because IAA builds up on the lower side, inhibiting root elongation and promoting shoot elongation.

Les pousses sont géotropiquement négatives (poussent vers le haut) et les racines sont géotropiquement positives (poussent vers le bas) car l'IAA s'accumule sur le côté inférieur, inhibant l'élongation des racines et la favorisant dans les pousses.

Front Describe and explain the geotropic responses in shoots and roots.
Back Geotropism in shoots and roots:
  • Shoots - negatively geotropic, roots - positively phototropic
  • This is because IAA inhibits cell elongation in roots & promotes it in shoots
  • In both, IAA builds up on lower side of a horizontal shoot/root:
    • In roots, it inhibits cell elongation on the lower side, causing growth downwards
    • In shoots, it promotes cell elongation on lower side, causing growth upwards

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