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Plant Hormones

  • Auxins produced at the tops of roots and shoots cause cell elongation, prevent leaf abscission, maintain apical dominance, control tropisms and stimulate the release of ethene for fruit ripening.
  • Gibberellins cause stem elongation, the breaking of dormancy and the use of food stores during germination and pollen tube growth during fertilisation.
  • Ethene causes fruit ripening and leaf fall.
  • ABA (abscisic acid) maintains dormancy, stimulates antifreeze production and stomatal closing in response to abiotic stress.

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Specification: OCR Biology A (H420), A-level, 5.1.5 Plant and animal responses. Topic: Plant Responses.

Key terms in this lesson

Hormone
A chemical messenger, secreted directly into the blood by an endocrine gland, that travels to target cells and alters their activity.
Tropism
A directional growth response of a plant towards or away from a directional stimulus, such as light or gravity.
Apical dominance
The suppression of the growth of lateral (side) buds by auxin produced in the apical (tip) bud.
Abscission
The shedding of leaves, or fruit, from a plant, brought about by enzymes that digest cell walls in the abscission zone.

More in Plant Responses

All 19 lessons in Plant Responses · All OCR A-level Biology topics