Plant diseases & defences

• plants need mineral irons from the soil so if they're on to enough plants suffer deficiency symptoms
• plants can get infected by viral, bacterial and fungal pathogens. they can also be infested by insects
• signs of plant disease: stunted growth, spots on leaves, patches of Decay, abnormal growths, malformed stems or leaves, discolouration
• plants have physical, chemical and mechanical defences
• physical defences

  • waxy cuticle - provides a barrier
  • cell walls made from cellulose
  • layers of dead cells around the stem - barrier to stop pathogens
• chemical defences

  • some can produce antibacterial chemicals which kill bacteria e.g mint plant
  • produce poisons which can deter herbivores e.g tobacco plants
• mechanical defences

  • have thorns and hairs to stop animals from eating them
  • leaves that droop or curl when something touches them to move away from things
  • mimic other organisms e.g passion flowers has leaves which look like butterfly eggs to stop butterflies from laying their eggs there
• nitrates are needed to make proteins and therefore growth a lack of nitrates cause stunted growth
• magnesium ions are needed for making chlorophyll for photosynthesis. Without enough magnesium, plants suffer from chlorosis and have yellow leaves.