Chemical control in plants

  • explain that stomata have daily rhythms of opening and closing and also respond to changes in environmental conditions to allow diffusion of carbon dioxide and regulate water loss by transpiration
  • describe the structure and function of guard cells and explain the mechanism by which they open and close stomata
  • describe the role of abscisic acid in the closure of stomata during times of water stress (the role of calcium ions as a second messenger should be emphasised)
  • explain the role of auxin in elongation growth by stimulating proton pumping to acidify cell walls
  • describe the role of gibberellin in the germination of wheat or barley
  • explain the role of gibberellin in stem elongation including the role of the dominant allele, Le, that codes for a functioning enzyme in the gibberellin synthesis pathway, and the recessive allele, le, that codes for a non-functional enzyme