Chapter 5

• 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
• Growing bacteria in a lab

  1. Sterilise equipment

  2. Use agar gel

  3. Keep petri dish lid closed
• Bacterial reproduction equation


  Calculates number of bacteria after a given time, based on initial number and division rate
• Salmonella is a common bacterial infection from raw meat and eggs
• Bacterial infections in plants can cause abscesses called galls
• Scientists use bacterial infections in plants to genetically modify them</b>
• Viral infections are more common in plants than bacterial infections
• Tobacco mosaic virus infects many plant species, causing stunted growth and discoloration
• There is no treatment for tobacco mosaic virus, so genetically modified virus-resistant plants are grown
• Measles is a serious viral disease, but can be prevented by vaccination
• 145,000 people globally still die from measles each year due to lack of vaccination
• 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 in people

  • 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


  • Very common infection on rose plants
  • Leaves turn yellow and weakens photosynthesis
  • Flowers don't grow as well
• Reducing spread of rose black spot

  1. Use chemical fungicides

  2. Chop off infected leaves