preventing and identifying disease

• Physical defence system within plants

  • Waterproof waxy cuticle - surface barrier preventing the entry of pathogens
  • Cellulose cell wall - further barrier against pathogens
• Chemical barriers in plants

  • Secretion of toxins to reduce damage by pests e.g. stinging nettles
  • Production of antibacterial chemicals that kill bacterial pathogens
• Medicines derived from plants

  • Quinine - comes from bark and treats malaria
  • Aspirin - painkiller developed from a chemical found in bark
• Importance of plant defence systems

  • Plants are producers so all organisms higher up in food chains rely upon their survival and ability to fight disease
  • Important in maintaining human food security
• How plant diseases can be detected and identified in the field

  1. Observation of symptoms

  2. Analysis of the distribution of infected plants

  3. Changing environmental conditions to eliminate other causes
• How plant diseases can be detected and identified in the lab

  1. Detection of foreign antigens in a sample of plant tissue using monoclonal antibodies

  2. Analysis of DNA to identify any pathogen DNA in a tissue sample
• Non-specific defence

  Always present, same for all organisms, prevents pathogens from entering the body
• Body's physical defence system

  • Skin - protective surface barrier
  • Blood clotting - platelets seal wounds preventing entry of pathogens into the blood
  • Respiratory tract - mucus traps pathogens, cilia waft mucus to the back of the throat where it is swallowed
• Immune system

  The body's defence against pathogens once they have entered the body, aims to prevent or minimise disease caused by pathogens
• How white blood cells detect pathogens


  Pathogens have unique antigens on their surface which are detected by specialised receptors on white blood cells
• How the immune system destroys pathogens

  1. When your B-lymphocytes come across an antigen they produce antibodies

  2.Antibodies bind to new evading pathogen so it can be destroyed by other WBC's

  3.The antibodies produced are specific to the pathogen

  4. Antibodies are produced rapidly and find similar pathogens

  
• Vaccination

  Injecting dead or inactive pathogens into the body. These pathogens carry antigens so although harmless your body makes antibodies to destroy them.

  These antigens trigger memory lymphocytes, so if live pathogens of the same type get into the body, the memory lymphocytes will cause a fast secondary immune response, and you are less likely to get infected

  
• Components of a vaccine

  Dead, weakened or inactivated pathogens with their antigens still present
• pros of vaccinations

  • Herd immunity - vaccination of a significant proportion of the population gives some protection to individuals who are not immune
  • Helps to prevent epidemics and pandemics
• cons of vaccinations

  • May have a bad reaction to a vaccine (eg swelling)
  • Not guaranteed to work