GCSE Biology (B3)

• Microorganisms


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


  Microorganisms that can cause disease
• Communicable/infectious diseases


  Diseases caused by pathogens that can spread from person to person
• Types of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• How pathogens spread


  1. Through the air

  2. Through contaminated food and water

  3. Through direct contact
• Pathogens spread through the air

  Carried in tiny droplets expelled when coughing or sneezing
• Pathogens spread through contaminated food and water


  Example: Cholera is spread by drinking contaminated water, Salmonella is spread by eating contaminated food
• Pathogens spread through direct contact

  Example: Athlete's foot is spread by walking barefoot on contaminated surfaces
• Methods to reduce pathogen spread

  • Being hygienic (washing hands, cleaning cooking items)
  • Killing vectors (using insecticides)
  • Vaccinating people
  • 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
• 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 to infect other cells
• 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


  • Spread by sexual contact or sharing bodily fluids
  • Causes a deficient immune system
  • Initially causes flu-like symptoms
  • Can develop into AIDS if left untreated
  • Can be managed with antiretroviral drugs
• Tobacco mosaic virus (TMV)


  • Affects plants, not humans
  • Causes discoloured patches on leaves, reducing photosynthesis and plant growth
• Viruses are quite hard to explain
• When using the term HIV, you're referring to the virus, not the disease
• AIDS is classed as a disease or syndrome in which the person's immune system can't cope anymore
• 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
• In this video, we're going to focus on the few bad bacteria that infect humans and cause disease
• 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 might produce toxins which make us feel ill by damaging our cells and tissues
• Bacterial disease


  • Salmonella
  • Gonorrhea
• Salmonella


  Bacteria that causes food poisoning, often from contaminated chicken
• Salmonella generally passes by itself within a week, and people just need to stay well hydrated
• Gonorrhea


  Sexually transmitted bacterial disease
• Fungi


  Eukaryotic organisms, can be unicellular or multicellular
• Fungi


  • Yeast
  • Mushrooms
• Multicellular fungi


  • Have long thread-like structures called hyphae which come out of the main body and spread through the soil
• Hyphae spreading


  1. Can spread over plants or even penetrate human skin and cause disease

  2. 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
• Rose black spot fungus spreading

  Reduces the plant's ability to photosynthesize, so they don't grow so well
• Treating rose black spot

  1. Chop off all infected leaves and destroy them

  2. Spray the plant with fungicides
• Protists


  Eukaryotic organisms, can be single-celled or multi-celled
• Parasitic protists


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