infection and response

• Pathogens


  Microorganisms that enter the body and cause communicable disease (infectious)
• Pathogens


  • Plants and animals can be infected by them
• Viral Diseases


  Diseases caused by viruses
• Viral Diseases


  • Measles
  • HIV
  • Tobacco mosaic virus
• Measles


  • Spread by droplets of liquid from sneezes and coughs
  • Symptoms include a red rash on the skin and a fever
  • Can be serious or even fatal and can lead to pneumonia
  • Most people are vaccinated against measles when they are very young
• HIV


  • Spread by sexual contact or exchanging body fluids
  • Can be controlled by antiviral drugs which stop the viruses replicating
  • Attacks the cells in the immune system
  • If the immune system is badly damaged, the body cannot cope with other infections - this is the late stage and is called Aids
• Tobacco mosaic virus


  • Affects plants
  • Parts of the leaves become discoloured
  • This means plants cannot carry out photosynthesis, affecting the plants growth
• Bacterial Diseases


  Diseases caused by bacteria
• Bacterial Diseases


  • Salmonella
  • Gonorrhoea
• Salmonella


  • Causes food poisoning
  • Symptoms include fever, stomach cramps, vomiting and diarrhoea
  • Caused by the toxins produced by the bacteria
  • Food contaminated with salmonella can give you food poisoning
  • Most poultry in the UK will have had a vaccination against salmonella
• Gonorrhoea


  • A sexually transmitted bacterial disease, passed on by sexual contact
  • Symptoms include pain when urinating and thick yellow/green discharge from the vagina or penis
  • To prevent the spread, people should be treated with antibiotics and use a condom
• How to prevent the spread of pathogens

  • Being hygienic - washing hands thoroughly
  • Destroying vectors - killing vectors by using insecticides or destroying their habitat
  • Isolation - isolating an infected person will prevent the spread
  • Vaccination - people cannot develop the infection and then pass it on
• Fungal Diseases


  Diseases caused by fungi
• Fungal Diseases


  • Rose black spot
• Rose black spot


  • Shows as black spots on the leaves of the plant
  • Means less photosynthesis occurs, so the plant does not grow as well
  • Spread by the wind or the water
  • Can be treated by using fungicides and taking the leaves off the infected plant
• Protist Diseases


  Diseases caused by protists
• Protist Diseases


  • Malaria
• Malaria


  • Caused by a protist
  • Mosquitoes are the vectors, becoming infected when they feed on an infected animal
  • The protist is inserted into the blood vessel
  • Malaria can cause fever and it can also be fatal
• Bacteria


  • Small cells that can reproduce very quickly in the body
  • They produce toxins that make you feel ill, damaging your cells and tissues
• Viruses


  • Much smaller than bacteria
  • They can also reproduce quickly in the body
  • Viruses live inside your cells where they replicate
  • They then burst out of the cell, releasing new viruses
• Protists


  • Eukaryotes (multicellular)
  • Some are parasites which live on or inside other organisms, often carried by a vector
• Fungi


  • Sometimes single celled, others have hyphae that grow and penetrate human skin and the surface of plants
  • They can produce spores which can spread to other plants
• How Pathogens Are Spread

  • Water - by drinking dirty water, e.g. cholera
  • Air - carried by air and breathed in, e.g. influenza
  • Direct contact - touching contaminated surfaces including the skin, e.g. athlete's foot
• Plant Deficiency Symptoms


  • Stunted growth
  • Yellow leaves
  • Patches of decay
  • Abnormal growth
  • Malformed stems or leaves
  • Discolouration
• Plant Defences


  • Physical - waxy cuticle, cell walls, layer of dead cells
  • Mechanical - thorns, hairs, leaves that droop or curl, mimicking other organisms
• White Blood Cells


  • Phagocytosis - engulf pathogens and digest them
  • Produce antitoxins to neutralise toxins
  • Produce antibodies that lock onto pathogen antigens, allowing white blood cells to destroy the pathogens
• Antibodies are specific to one antigen and will only work on that pathogen
• Painkillers


  Relieve the pain and symptoms, but do not tackle the cause
• Antibiotics


  Kill the bacteria causing the problem, but do not work on viruses
• Viruses are very difficult to kill because they live inside the body cells
• Stages of Drug Testing

  • Pre-clinical testing - Drugs tested on human cells/tissues, then tested on living animals
  • Clinical testing - Tested on healthy human volunteers, starting with low dose then testing on people with the illness to find optimum dose
• Placebo


  A substance that is like the drug but does not do anything
• Placebo Effect


  When the patient thinks the treatment will work even though their treatment isn't doing anything
• Blind Trial


  When the patient does not know whether they are getting the drug or the placebo
• Double-Blind Trial


  When both the doctor and the patient do not know whether they are getting the drug
• Vaccination


  • Involves an injection of a dead or weakened version of the pathogen
  • Carries antigens which cause the body to produce antibodies to attack the pathogen
  • If infected again, the white blood cells can produce antibodies quickly
• Body's Defence System


  • Skin acts as a barrier to pathogens
  • Hairs and mucus in nose trap particles
  • Trachea and bronchi secrete mucus and have cilia to trap pathogens
  • Stomach contains hydrochloric acid to kill pathogens
• Monoclonal Antibodies


  Identical antibodies produced by fusing a B lymphocyte from a mouse with a tumour cell to create a hybridoma cell
• Uses of Monoclonal Antibodies

  • Pregnancy testing
  • Treating diseases - anti-cancer drugs can be attached to target cancer cells
  • Research to find specific substances
• Monoclonal antibodies have more side-effects than originally thought, so are not used by doctors as much as was first thought