B3.3 - Plant Disease

• How can plant diseases be detected?

  • stunted growth
  • spots on leaves
  • areas of decay (rot)
  • growths
  • malformed stems or leaves
  • discolouration
  • the presence of pests.
• How can plant disease identification be made?

  • reference to a gardening manual or website
  • taking infected plants to a laboratory to identify the pathogen
  • using testing kits that contain monoclonal antibodies.
• How can plants be infected?

  • A range of viral, bacterial, and fungal pathogens
  • Insects
• What is stunted growth caused by?

  Nitrate deficiency
• What is chlorosis caused by?

  Magnesium deficiency
• What are nitrate ions needed for?

  Protein synthesis and therefore growth
• What are magnesium ions needed for?

  Chlorophyll production
• Physical defences of plants to resist invasion of microorganisms

  • Cellulose cell walls.
  • Tough waxy cuticle on leaves.
  • Layers of dead cells around stems (bark on trees) which fall off.
• Chemical plant defence responses

  • Antibacterial chemicals.
  • Poisons to deter herbivores.
• Mechanical adaptations


  • Thorns and hairs deter animals.
  • Leaves which droop or curl when touched.
  • Mimicry to trick animals.