B3

• ways pathogens spread

  1. Through the air - Diseases such as influenza and measles can spread via tiny droplets of saliva that we expel when we cough or sneeze.
  2. Contaminated water - Diseases such as cholera can spread through water sources contaminated by the diarrhoea of infected people. 
  3. Contaminated food - Diseases such as salmonella are spread by eating food which has been infected with salmonella, and then not cooked properly.
  4. Direct contact - Athlete's foot is spread by walking barefoot on surfaces contaminated with the fungi.
• reduce spread of communicable diseases

  Improved hygiene, such as washing hands and cleaning surfaces 

  Vaccination 

  Killing the vectors that carry pathogens 

  Isolating or quarantining people who are infected 
• viruses are not living organisms so they don't have cells
• viruses are about 10,000 times smaller than the average plant or animal cell
• virus multiplication

  1. Viruses can pass between humans via the air, contaminated food or water, or by direct contact.
  2. As they can't reproduce themselves, viruses have to enter one of our cells, and then use it to create multiple copies of the virus itself.
  3. Once there are lots of copies, the viruses cause the cell to burst, and then go on to infect neighbouring cells. 
• 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
• 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
• When referring to HIV, you're referring to the virus, not the 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
• Salmonella bacteria

  • Causes food poisoning
  • Can be caught from any food 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
• Gonorrhea


  • A sexually transmitted disease (STD)
  • Passed on through sexual contact, e.g. unprotected sex
• Symptoms of gonorrhea

  • Pain when urinating
  • Thick yellow-green discharge from the vagina or penis
• Prevention of STDs

  Avoiding unsafe sex and using barrier methods of contraception like condoms
• Treatment of gonorrhea

  Used to be cured by common antibiotic penicillin, but now many strains are resistant to penicillin, so rarer and more expensive antibiotics are used
• STD - Sexually Transmitted Disease 

   STI   - Sexually Transmitted Infection
• Fungi


  Eukaryotic organisms like plants and animals, 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 the 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
• 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)
• Physical and chemical barriers

  Stop 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 little hairs and mucus that can trap pathogens and particles in the air