CIE A Level Biology (9700) 2019-2021

Revision Notes

15.2.3 The Role of Gibberellin in Germination of Barley

The Role of Gibberellin in Germination of Barley

  • Gibberellins are a type of plant growth regulator involved in controlling seed germination and stem elongation
  • When a barley seed is shed from the parent plant, it is in a state of dormancy (contains very little water and is metabolically inactive)
  • This allows the seed to survive harsh conditions until the conditions are right for successful germination (eg. the seed can survive a cold winter until temperatures rise again in spring)
  • The barley seed contains:
    • An embryo – will grow into the new plant when the seed germinates
    • An endosperm – a starch-containing energy store surrounding the embryo
    • An aleurone layer – a protein-rich layer on the outer edge of the endosperm
  • When the conditions are right, the barley seed starts to absorb water to begin the process of germination
  • This stimulates the embryo to produce gibberellins
  • Gibberellin molecules diffuse into the aleurone layer and stimulate the cells there to synthesise amylase
    • In barley seeds, it has been shown that gibberellin does this by regulating genes involved in the synthesis of amylase, causing an increase in the transcription of mRNA coding for amylase
  • The amylase hydrolyses starch molecules in the endosperm, producing soluble maltose molecules
  • The maltose is converted to glucose and transported to the embryo
  • This glucose can be respired by the embryo, providing the embryo with the energy needed for it to grow


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

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