gcse biology

• Pathogens


  Microorganisms that cause infectious disease, including viruses, bacteria, protists and fungi
• Pathogens


  • Can infect plants or animals
  • Spread through direct contact, by water or by air
• Viruses


  • Very small
  • Move into cells and use the biochemistry to make many copies of themselves
  • This leads to the cell bursting and releasing all of the copies into the bloodstream
  • The damage and destruction of the cells makes the individual feel ill
• Bacteria


  • Small
  • Multiply very quickly through dividing by a process called binary fission
  • Produce toxins that can damage cells
• Fungi

  • Some are parasitic, meaning they use humans and animals as their hosts
  • Can be single celled or have a body made of hyphae (thread-like structures)
  • Can produce spores which can be spread to other organisms
• Ways pathogens are spread

  • Direct contact-touching contaminated surfaces
  • By water-drinking or coming into contact with dirty water
  • By air-pathogens can be carried in the air and then breathed in
• Reducing the damage disease causes to populations

  1. Improving hygiene: Hand washing, using disinfectants, isolating raw meat, using tissues and handkerchiefs when sneezing

  2. Reducing contact with infected individuals

  3. Removing vectors Using pesticides or insecticides and removing their habitat

  4. Vaccination By injecting a small amount of a harmless pathogen into an individual's body, they can become immune so it will not infect them
• Viral diseases

  • Viruses are particularly dangerous as they can infect all types of cells and scientists are yet to develop medicines to cure them
  • Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection) and blindness
  • How it is spread: Droplet infection
  • How is it being prevented: Vaccinations for young children to reduce transmission
• HIV/AIDS

  • Initially flu-like symptoms, then the virus attacks the immune system and leads to AIDS (a state in which the body is susceptible to many different diseases)
  • How it is spread: By sexual contact or exchange of bodily fluids such as blood
  • How it is being prevented: Using condoms, not sharing needles, screening blood when it is used in transfusions, mothers with HIV bottle feeding their children instead of breastfeeding
  • The development to AIDS: Use of antiretroviral drugs stop the virus replicating in the body
• Tobacco mosaic virus


  • Symptoms: Discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield
  • How is it spread: Contact between diseased plants and healthy plants, insects act as vectors
  • How it is being prevented: Good field hygiene and pest control, growing TMV-resistant strains