17 June 2016

#124 Venus fly trap

The Venus fly trap is a carnivorous plant that obtains a supply of nigtrogen compounds by trapping and digesting small animals, mostly insects.

Anatomy of the Venus fly trap

  • Midrib = hinge
  • 2 lobes
  • glands that secrete digestive enzymes
  • 3 sensory hairs on each lobe that respond when they are deflected
  • nectar-secreting glands to attract insects
  • stiff outer-edges that interlock to trap insects

Electrical communication in plants

  • microelectrodes in leaf cells detect changes in potential difference.
  • depolarisation results from the outflow of Cl-
  • repolarisation is achieved by the outflow of  K+
  • action potentials travel along cell membranes, from cell to cell through plasmodesmata
  • these action potentials last longer and travel more slowly than in animal neurones

1. Sensory hair is deflected

2. Ca2+ channels at the base of the hair opens. Ca2+ flows in and generates a receptor potential.

3. Within 20 - 35 seconds, if 2 hairs get stimulated or 1 hair is stimulated twice, an action potential will spread acroos the lobe --> trap closes

Further stimulation (deflection of hairs) will force the edges of lobes to seal --> more Ca2+  enter cells --> stimulates the exocytosis of vesicles containing digestive enzymes.

Once the insect is digested, the cells on the upper surface of the midrib grow slowly so the leaf reopens and tension builds in the cell walls of the midrib so the trap is set again.

Adaptations to reduce waste of energy

  • one hair stimulated will not close the trap e.g.: wind, raindrop
  • gap between stiff outer edges allow small insects to escape because they are not worth it

   Syllabus 2016-2018

15.2  Control and co-ordination in plants

Plant co-ordination systems involve rapid responses as in the case of the Venus fly trap, but also complex interactions between plant growth regulators, such as auxin and gibberellin. Plants respond quite differently to different concentrations of plant growth regulators.

a) describe the rapid response of the Venus fly trap to stimulation of hairs on the lobes of modified leaves and explain how the closure of the trap is achieved

b) explain the role of auxin in elongation growth by stimulating proton pumping to acidify cell walls

c) describe the role of gibberellin in the germination of wheat or barley

d) 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

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