B5: communicable diseases

• Communicable diseases

  Diseases that can be passed on, involving a pathogen
• Types of pathogens

  • Fungi
  • Viruses
  • Bacteria
  • Protists
• Pathogen

  An organism that can cause disease
• Ways diseases can spread

  • Direct contact (e.g. STIs)
  • Air (e.g. flu)
  • Water (e.g. cholera)
• Factors affecting susceptibility to communicable diseases

  • Malnutrition weakening immune system
  • Genetics affecting immune system
  • Location and prevalence of disease
• Viruses

  Incredibly small, need host cells to reproduce, hard to treat with antibiotics
• Bacteria

  Larger than viruses, can reproduce independently, often treated with antibiotics
• Pathogens (viruses and bacteria) inside the body

  Produce toxins that make you feel ill
• Bacterial reproduction equation

  Calculates number of bacteria after a given time based on initial number and division rate
• Bacterial infections

  • Salmonella
  • Bacterial infections in plants
• Viral infections in plants

  • Tobacco mosaic virus
• Viral infections in humans

  • HIV
  • Measles
• Measles can be fatal, especially in the elderly and young with poor immune systems, but is almost eradicated in the UK due to vaccination
• Fungal infections are also a type of communicable disease
• Viruses

  Can infect people
• Viral diseases

  • HIV
  • Measles
• Measles

  • Characterised by itchy spots
  • Can be fatal in elderly and young with poor immune systems
  • Almost eradicated in UK due to MMR vaccine
• 145,000 people died globally due to measles, this number could be significantly lower if the vaccine was taken in other countries
• Fungal infections

  Less common in people, more common in plants
• Fungal infection

  • Athlete's foot
• Athlete's foot


  • Found in sports people due to high temperatures and sweat in shoes
  • Needs moisture to grow
• Fungal infections inside the body are more difficult to treat
• Fungal infection in plants

  • Rose black spot
• Rose black spot

  • Causes leaves to turn yellow and weakens photosynthesis
  • Reduces flower growth
  • Spreads via airborne spores
• Protists


  Parasites carried by a vector (e.g. mosquito for malaria)
• Malaria

  • Parasite travels in human bloodstream and affects liver and red blood cells
  • Causes recurrent fever and shaking
  • Can be fatal
  • Weakens affected person over time
• Malaria can be treated if diagnosed early, and prevention is the main strategy (e.g. mosquito nets)
• Ways to control the spread of diseases

  1. Hygiene (e.g. hand sanitisers, safe disposal bins in hospitals)

  2. Government measures (e.g. 2 metre rule for COVID-19)

  3. Vaccinations (can provide herd immunity)

  4. Isolation of infected individuals
• Immune system

  Host defence system comprising biological structures and processes that protect against diseases
• Immune system defences

  • Skin as a physical barrier
  • Saliva and mucus trapping and removing pathogens
  • Stomach acid killing bacteria
  • Lymphocytes producing antibodies and antitoxins
  • Phagocytes engulfing and destroying pathogens
• Plant defences

  • Chemical barriers like antibiotics
  • Physical barriers like waxy cuticle and cellulose layers
  • Defences against herbivores (e.g. poisons, spikes, curling up, mimicking infection)
• Plants can also suffer from mineral deficiencies, which stunt growth and cause discolouration