Infection & Response

• Microorganisms


  A group of tiny organisms including bacteria, viruses, protists and fungi
• Pathogens


  Microorganisms that can cause disease
• Communicable/infectious diseases


  Diseases that can spread from person to person and affect both animals and plants
• How pathogens spread from person to person


  1. Through the air (e.g. coughing, sneezing)

  2. Through contaminated food and water

  3. Through direct contact
• Pathogens spread through the air


  • Influenza virus
  • Measles virus
• Pathogens spread through contaminated food and water

  • Cholera (bacterial disease spread by contaminated water)
  • Salmonella (bacteria spread by contaminated food, particularly chicken)
• Pathogens spread through direct contact


  • Athlete's foot (fungal infection spread by walking barefoot on contaminated surfaces)
• Ways to reduce the spread of pathogens

  1. Being hygienic (e.g. washing hands, cleaning cooking items)

  2. Killing vectors (e.g. using insecticides to kill mosquitoes)

  3. Vaccinating people

  4. Quarantining infected people
• The best way to prevent a pathogen from spreading is to vaccinate everybody
• Quarantine is generally only used for really serious diseases that could harm others if spread
• Viruses


  • Not cells, not living, but considered organisms
  • About 10,000 times smaller than animal cells
  • Can't reproduce by themselves, but can use a host cell's machinery to make copies of themselves
  • Can burst the host cell to release new viruses
• Viruses colonizing and bursting host cells


  Damages the body and makes us feel ill
• Viral diseases covered


  • Measles
  • HIV
  • Tobacco mosaic virus
• Measles virus


  • Spread by droplets when an infected person coughs or sneezes
  • Causes a red rash and fever
  • Rare in UK due to vaccination
• HIV


  • Human Immunodeficiency Virus
  • Spreads through sexual contact or sharing bodily fluids
  • Causes a deficient immune system
  • Initially causes flu-like symptoms, then weakens the immune system over time
  • Can develop into AIDS if left untreated
  • Treatable with antiretroviral drugs
• Tobacco mosaic virus (TMV)


  • Affects plants, not humans
  • Causes discolored patches on leaves, reducing photosynthesis and plant growth
• Viruses are quite hard to explain as they aren't cells and aren't living, but we still consider them to be organisms
• Most bacteria don't have anything to do with humans, and the ones that do actually help us
• There are trillions of bacteria in your intestines right now helping you break down your dinner
• Bacteria


  Single-celled organisms about 100 times smaller than our own cells
• Bacteria can replicate rapidly within our bodies because of the good food supply
• Bacteria


  They might produce toxins which make us feel ill by damaging our cells and tissues
• Bacterial disease


  • Salmonella
• Salmonella causes food poisoning and we can catch it from any food that has been contaminated with the bacteria, most often by eating chicken that caught the disease
• In the UK, most chickens have to be vaccinated against salmonella, so it's relatively rare
• Symptoms of salmonella


  • Fever
  • Stomach cramps
  • Vomiting
  • Diarrhea
• Salmonella generally passes by itself within a week, and people just need to stay well hydrated and have a sick bowl close by
• Bacterial disease


  • Gonorrhea
• Gonorrhea


  A sexually transmitted disease (STD) passed on through sexual contact, for example having unprotected sex
• Symptoms of gonorrhea


  • Pain when urinating
  • Thick yellow-green discharge from the vagina or penis
• We used to use a common antibiotic penicillin to treat gonorrhea, but now a lot of gonorrhea strains are resistant to penicillin, so we're using rarer and more expensive antibiotics
• The best prevention for gonorrhea is avoiding unsafe sex and using barrier methods of contraception like condoms
• Fungi


  Eukaryotic organisms, can be unicellular or multicellular
• Fungi


  • Yeast (unicellular)
  • Mushrooms (multicellular)
• Fungi


  • Have long thread-like structures called hyphae which come out of the main body and spread through the soil
  • Hyphae can spread over plants or even penetrate human skin and cause disease
  • Hyphae can produce spores which spread easily and grow into new fungi
• Fungal disease


  • Rose black spot
• Rose black spot


  • Causes purple or black spots to form on the leaves of plants, especially roses
  • As the fungus does more damage, the leaves can start to turn yellow and drop off
• Treating rose black spot

  1. Chop off all infected leaves and destroy them

  2. Spray the plant with fungicides which kill any fungus
• Protists


  Eukaryotic organisms, can be single-celled or multi-celled, majority are single-celled
• Protist parasites


  Live on or inside other organisms and survive at that other organism's expense