describe the role of gibberellin in the germination of barley (see 16.3.4)

explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, that codes for a functional enzyme in the gibberellin synthesis pathway, and the recessive allele, le, that codes for a non-functional enzyme

describe the structure and function of guard cells and explain the mechanism by which they open and close stomata