Control and coordination in plants

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  • Created by: portia
  • Created on: 03-05-17 18:29

Most plant responses involve changing some aspect of their growth to respond to factors such as gravity, light and water availability.

Plants can also respond fairly quickly to changes in carbon dioxide concentration, lack of water, grazing by animals and infection by fungi and bacteria. Some of these responses are brought about by quick changes in turgidity, as when stomata respond to changes in humidity, carbon dioxide concentration and water availability

Electrical communication in plants

  • like animal cells plant cells have electrochemical gradients across their cell surface membranes
  • they also have resting potentials
  • like in animal cells, action potentials are triggered when the membrane is depolarised
  • in atleast some species responses to stimuli are coordinated by action potentials
  • the 'sensitive plant', Mimosa, responds to touch by folding up its leaves
  • microelectrodes inserted in leaf cells detect similar changes in pd to action potentials in animals
  • the depolarisation results from the outflow of negatively charged Cl- ions and not from the influx of positively charged sodium ions
  • repolarisation is achieved in the same way by the outflow of K+ ions
  • many plant cells can transmit waves of electrical activity similar to those transmitted along neurones of animals
  • the action potentials travel along the plant cell membrane from cell to cell through plasmodesmata that are lined by cell membrane

Many different stimuli trigger action potentials in plants

  • chemicals coming into contact with a plant's surface trigger action potentials
    • dripping a solution of acid of similar pH to acid rain on soya bean leaves causes action potentials to sweep across them
    • in potato plants, Colorado beetle larvae feeding on leaves induce action potentials
    • no-one knows the effect, if any, these action potentials have but it is thought they may bring about changes in metabolic reactions taking place in some parts of the plant

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

  • the specialised leaf is divided into two lobes either side of a midrib
  • the inside each lobe is often red and has nector-secreting glands around the edge to attract insects
  • each lobe has 3 stiff sensory hairs that respond to being deflected
  • the outer edges of the lobes have stiff hairs that interlock to trap the insect inside
  • the surface of the lobes has many enzyme secreting glands for the digestion of trapped insects
  • the touch of a fly or other insect on the sensory hairs on the inside of the folded leaves of the Venus fly trap stimulates action potentials that travel very fast across the leaf causing it to fold over and trap the insect

The deflection of a sensory hair activates calcium ion channels in cells at the base of the hair

  • these channels open to enable calcium ions to flow in to generate a receptor potential
  • if two of these hairs are stimulated within a period of 20 to 35 seconds, or one hair is touched twice within the same time interval, action…

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