Animal and Plant Defences

• Indirect transmission - a disease is transmitted from one organism to another via a vector
• Vector - Organism that carries a pathogen from one host to another. usually these are insects
• Methods of Transmission (Direct)

  • Physical contact
  • Contaminated food/ drink/ surfaces
  • Droplet infection
  • Spores
  • Bodily fluids
• Types of Plant defences

  • Passive defences - present all the time
  • Active defences - Only used/produced when infection occurs
• Passive plant defences

  Present before infection occurs

  • Cellulose cell wall - physical barrier, contains chemical defences
  • Waxy cuticles - physical barrier, reduces spread of water-bone pathogens
  • Lignin - indigestible waterproofing substance (in the xylem)
  • Bark - contains chemical defences
• Passive Chemical Plant Defences

  A lot of energy is required to produce antimicrobial chemicals

  • Terpenes
  • Alkaloids
  • Hydrolytic (digestive) enzymes
• Active plant defences - physical

  • Close stomata - pathogens detected via changes in cytoplasmic volume in guard cells so stomata close
  • Callose - large, insoluble polysaccharide deposited between the cell wall and plasma membrane
  • Tyloses formation - Swellings that block xylem vessels to restrict pathogen spread
• Active plant defences - chemical

  Oxidative bursts produce highly reactive oxygen molecules which damage pathogen cells.

  Antimicrobial chemical production is increased

  1. Saponins destroy plasma membrane of fungal cells
  2. Phytoalexins inhibit pathogen growth

  Infected cells are deliberately sacrificed in necrosis; limits the spread of the pathogen to the rest of the plant
• Animal defence types

  • Primary defences - stop pathogens entering the body
  • Secondary defences - actions of phagocytes to kill pathogens that surpass the primary defences