Plant Diseases

• Aphids


  Use their sharp mouthparts to extract sap from the plant phloem, weakening the plant. They are also vectors who can transfer pathogens from diseased plants to healthy plants.
• Reducing the number of aphids

  1. Chemical pesticides

  2. Biological pest control - using ladybirds
• Nitrate ions


  Required to convert sugars into proteins which are required for the plant to grow. If there is not an adequate supply, the growth of the plant will be stunted.
• Magnesium ions


  Required to synthesise chlorophyll, which absorbs light energy during photosynthesis. If there is not an adequate supply, the leaves cannot photosynthesise properly and they turn yellow (chlorosis).
• Symptoms of disease in plants

  • Stunted growth (lack of nitrate ions)
  • Spotted leaves (eg. rose black spot fungus)
  • Decay/rotting
  • Growths
  • Malformation of stems/leaves
  • Discolouration
  • Presence of pests
• Identifying plant disease


  1. Reference to a gardening website or manual

  2. Laboratory testing

  3. Monoclonal antibody test kits
• Physical defence responses used by plants

  • Cellulose cell walls
  • Tough waxy cuticle on leaves
  • Outside layer on stems/bark on trees
  • Leaf fall
• Chemical defence responses used by plants

  • Antibacterial chemicals
  • Poisons
• Mechanical defence responses used by plants

  • Thorns and hairs to deter animals
  • Leaves that droop/curl on contact
  • Mimicry to trick animals