things

• How plant diseases can be detected and identified in the field

  1. Observation of symptoms , books and online resources aid identification

  2. Analysis of the distribution of infected plants can indicate the type of pathogen involved , e.g the pathogen may be airborne if there is random distribution or there may be a problem with the soil if they are all in one area

  3. Changing environmental conditions to eliminate other causes such as nutrient deficiencies or water logged soil
• Many diseases may have similar symptoms, making it difficult to identify a disease using symptoms alone
• 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
• 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. B-lymphocytes (type of WBC) produce antibodies in response to a particular antigen on the pathogen present

  2. Each antibody is specific to an antigen and binds to it

  3. Antibodies 'tag' pathogens or clump them together, disabling them so that they can be killed by other WBCs
• Memory lymphocytes

  WBCs produced in response to a foreign antigen that remain in the body after the pathogen has been destroyed, provide immunity - if the body is re-infected, antibodies are produced more rapidly due to the memeory lymphocytes and the pathogen is destroyed before it can produce disease symptoms
• Vaccination

  Deliberate exposure of an individual to foreign antigens, triggers an immune response (produces antibodies) and provides immunity (due to memory cells), the individual does not contract the disease that they are being immunised against
• antibody

  produced by b lymphocytes and is specific to a certain antigen , clumps pathogen cells together and disables them making it easier for other cells to kill them