CIE A Level Biology (9700) exams from 2022

Revision Notes

15.2.1 Electrical Communication in the Venus Flytrap

Electrical Communication in the Venus Flytrap

  • Plants possess communication systems that enable them to coordinate the different parts of their bodies
  • The Venus flytrap is a carnivorous plant that gets its supply of nitrogen compounds by trapping and digesting small animals (mainly insects)
  • The specialised leaf is divided into two lobes either side of a midrib
  • The inside of the lobes is red and has nectar-secreting glands on the edges to attract insects
  • Each lobe has three stiff sensory hairs that respond to being touched
  • If an insect (eg. a fly) touches one of these hairs with enough force, action potentials are stimulated, which then travel very fast across the leaf
  • These action potentials cause the two lobes to fold together along the midrib, capturing the insect

How the closure of the trap is achieved

  • If one of the sensory hairs is touched with enough force, calcium ion channels in cells at the base of the hair are activated
  • When these channels open, calcium ions flow in and generate a receptor potential
  • If two of the sensory hairs are stimulated within a period of about 30 seconds, or one hair is stimulated twice within this period, action potentials will travel across the trap and cause it to close
    • When the trap is open the lobes of the leaf are convex in shape but when the trap is triggered, the lobes quickly become concave, bending downwards and causing the trap to shut – it is thought this occurs as a result of a release of elastic tension in the cell walls
  • Sealing the trap requires ongoing activation of the sensory hairs – the prey trapped inside provides this ongoing stimulation, generating further action potentials
  • Further stimulation of the sensory hairs stimulate calcium ions to enter gland cells where they stimulate the exocytosis of vesicles containing digestive enzymes
  • The trap then stays shut for up to a week to allow the prey to be digested and the nutrients from it to be absorbed by the plant


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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