Plant responses to herbivory

• State examples of physical defences

  • Thorns
  • Barbs
  • Spiny leaves
  • Fibrous and inedible tissues
  • Hairy leaves
  • Stings
  • Discourage consumption by herbivores
• what are alkaloids? what do alkaloids do as a chemical defence?

  • bitter nitrogenous compounds
  • drug- affects metabolism of animals that consume the plant and poisons them
  • eg- caffeine, nicotine, cocaine, and morphine
  • caffeine- toxic to fungi and insects. Can also spread through the soil and prevent germination of other plant seedlings, protecting plant from herbivores and other plant rivals
  • nicotine- toxic, transported to leaves and stored in vacuoles to be released when the leaf is eaten
• define what pheromones are

  Chemical made by an organism which affects the social behaviour of a different member of the same species
• Describe how pheromones affects a plant

  • Plant/tree attacked by insects
  • Pheromones released
  • Absorbed by leaves on other branches, which make callose to protect against attack
  • Nearby trees also prepare in response to signals
• What are volatile organic compounds? What effect do they have?

  • Act as pheromones between plants and other organisms
  • Diffuse through air in and around plant
  • Usually produced if attack is detected
  • Chemicals in saliva of insects may cause gene switching
  • causes neighbouring plants to also produce VOCs before they are attacked
  • some plants produce VOCs that attract predators of the pest organism
• How does the mimosa pusica respond to touch?

  • Leaves fold and collapse
  • Frighten larger herbivores, dislodge small insects on leaves
• How does the Venus flytrap work?

  • Trigger hairs
  • Insect contacts these, action potentials cause cells at the hinge to take up water
  • Causes leaf to close
  • Takes less than one second
• What are pheromones?

  Affect social behaviour of other organisms of the same species
• what are the two main chemical defences of plants against herbivory?

  • alkaloids
  • pheromones
• True or false? plants rely a lot on pheromones to communicate with each other

  FALSE- plants do not communicate socially a lot, so don't rely on pheromones a lot
• how do pheromones have an effect in roots?

  Some evidence that they are released in root systems and plants can communicate and tell if their neighbour is under water stress
• what does volatile mean?

  easily evaporated at normal temperatures