plant defence systems

• Physical responses


  • Cellulose cell wall difficult for microorganisms to penetrate
  • Waxy cuticle on leaves difficult for microorganisms to penetrate
  • Layers of dead cells (bark) around stems as a barrier to entry for microorganisms
• Chemical response


  • Plants release antibacterial chemicals to kill bacteria and prevent them attacking the plant
  • Plants release poisons to deter herbivores from grazing on the plant
• Mechanical defense system

  • Thorns or hairs that directly protect a plant from being eaten by a herbivore
  • Leaves that droop or curl when touched, which may scare herbivores
  • Mimicry, where a plant looks similar to a stinging nettle but has no sting, deterring herbivores
• Plants have three main defense systems against attack: physical responses, chemical responses, and mechanical defense systems
• Why do plants have throns


  to deter herbivors or stop them from damadging plant
• Explain two other possible reasons for the yellow leaves and stunted growth

  lack of magnesium so not enough chlorophyll for efficient photosynthesis

  not enough glucose to make proteins

  for growth

  lack of chlorophyll produced causes yellow leaves

  infected by pathogens of virus so leaves become discoloured

  infected by aphids which removes sugars from phloem so not enough glucose to make protiens for growth