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. Isolating/quarantining infected people
• Quarantine is generally only used for really serious diseases that could harm others if spread
• Fungi

  Eukaryotic organisms, can be unicellular or multicellular
• Examples of Fungi

  • Yeast (unicellular)
  • Mushrooms (multicellular)
• Structure of 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
• Example of 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
• Vectors

  Other organisms like insects that transport protists between different host organisms, but the vectors don't get the disease themselves
• Example of a Protist disease

  • Malaria
• How malaria spreads

  1. Mosquito feeds on infected animal and sucks up malaria parasites

  2. Mosquito then feeds on healthy person and transfers the parasites
• Malaria symptoms

  • Recurrent episodes of bad fevers, headaches, and feeling dreadful
  • Can be fatal in some cases
• Preventing protist diseases

  1. Reduce number of vectors (e.g. destroy mosquito breeding sites, use insecticides)

  2. Stop vectors from feeding on humans (e.g. use mosquito nets, repellents)
• 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 colonising and bursting host cells damages the body and makes us feel ill
• Examples of Viral diseases

  • 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
• Bacteria can replicate rapidly within our bodies because of the good food supply
• How do bacteria make us feel ill?

  Produce toxins which make us feel ill by damaging our cells and tissues
• 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
• Symptoms of salmonella

  • Fever
  • Stomach cramps
  • Vomiting
  • Diarrhea
• 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
• Examples of Bacterial diseases

  • Ghonorea
  • Salmonela
• Physical and chemical barriers stops pathogens from getting into the body
• Immune system

  Destroys pathogens that do make it into the body
• Skin

  • Acts as a physical barrier that pathogens can't get through
  • Secretes oils and antimicrobial substances that can kill pathogens
• Nose

  Has hairs and mucus that can trap pathogens and particles in the air
• Trachea and esophagus

  Only two tubes leaving the throat that pathogens can enter