Plant diseases and defences

• • nitrates needed to make proteins and therefore for growth
  • lack of nitrates can cause stunted growth
  • magnesium needed for chlorophyll, for photosynthesis
  • lack of magnesium causes chlorosis and yellow leaves
• physical defences:

  • waxy cuticle - barrier to stop pathogens entering
  • cell walls - physical barrier after waxy cuticle
  • layer of dead cells around stem - barrier to stop pathogens entering
• chemical defences:

  • antibacterial chemicals - kill bacteria e.g mint, witch hazel
  • poisons - deter herbivores e.g tobacco plants, foxgloves, nightshade
• mechanical defences:

  • thorns and hairs
  • drooping / curling leaves - prevent being eaten by knocking insects off, moving away from harmful things
  • mimicking— passion flower has yellow spots to look like butterfly eggs to stop other butterflies laying eggs there