Infection and Response

• Pathogens


  Microorganisms that cause infectious disease
• Types of pathogens


  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Viruses


  • Very small
  • Move into cells and use the biochemistry to make many copies of itself
  • 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
  • They produce toxins that can damage cells
• Protists


  • Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
• Fungi


  • Can be single celled or have a body made of hyphae (thread-like structures)
  • They can produce spores which can be spread to other organisms
• Ways pathogens are spread

  • Direct contact
  • By water
  • By air
• Direct contact


  Touching contaminated surfaces, kissing, contact with bodily fluids, direct skin to skin, microorganisms from faeces, infected plant material left in field
• By water


  Drinking or coming into contact with dirty water
• By air


  Pathogens can be carried in the air and then breathed in (a common example is the droplet infection, which is when sneezing, coughing or talking expels pathogens in droplets which can be breathed in)
• Ways to reduce the damage of disease

  • Improving hygiene
  • Reducing contact with infected individuals
  • Removing vectors
  • Vaccination
• Improving hygiene


  Hand washing, using disinfectants, isolating raw meat, using tissues and handkerchiefs when sneezing
• Removing vectors


  Using pesticides or insecticides and removing their habitat
• Vaccination


  Injecting a small amount of a harmless pathogen into an individual's body, they can become immune to it so it will not infect them. This means they cannot pass it on.
• Viruses


  • Particularly dangerous as they can enter all types of cells, and scientists are yet to develop medicines to cure them
• Measles symptoms include fever and red skin rash, can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection) and blindness
• How measles is spread

  Droplet infection
• How measles is being prevented

  Vaccinations for young children to reduce transmission
• HIV initially causes 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 HIV is spread

  By sexual contact or exchange of bodily fluids such as blood
• How HIV 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
• How HIV development to AIDS is being prevented

  Use of antiretroviral drugs (stop the virus replicating in the body)
• Tobacco mosaic virus causes discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield
• How tobacco mosaic virus is spread

  Contact between diseased plants and healthy plants, insects act as vectors
• How tobacco mosaic virus is being prevented

  Good field hygiene and pest control, growing TMV-resistant strains
• Bacterial diseases are on the rise as they are becoming resistant to antibiotics
• Salmonella food poisoning causes fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they secrete)
• How salmonella food poisoning is spread

  These bacteria can be found in raw meat and eggs, unhygienic conditions
• How salmonella food poisoning is being prevented

  • Poultry are vaccinated against Salmonella
  • Keeping raw meat away from cooked food
  • Avoid washing it
  • Wash hands and surfaces when handling it
  • Cook food thoroughly
• Gonorrhoea symptoms include thick yellow or green discharge from the vagina or penis, pain when urinating
• How gonorrhoea is spread

  It is a sexually transmitted disease spread through unprotected sexual contact
• How gonorrhoea is being prevented

  By using contraception such as condoms and antibiotics (used to be treated with penicillin but many resistant strains are developing)
• Rose black spot causes purple or black spots on leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early
• How rose black spot is spread

  The spores of the fungus are spread in water (rain) of by wind
• How rose black spot is being prevented

  By using fungicides or stripping the plant of affected leaves (have to be burnt)
• Malaria causes fevers and shaking (when the protists burst out of blood cells)
• How malaria is spread

  The vector is the female Anopheles mosquito, in which the protists reproduce sexually. When the mosquito punctures the skin to feed on blood, the protists enter the human bloodstream via their saliva.
• How malaria is being prevented

  • Using insecticide coated insect nets while sleeping
  • Removing stagnant water to prevent the vectors from breeding
  • Travellers taking antimalarial drugs to kill parasites that enter the blood
• Non-specific defence system


  • The skin
  • The nose
  • The trachea and bronchi
  • The stomach
• The skin


  • Acts as a physical barrier
  • It produces antimicrobial secretions to kill pathogens
  • Good microorganisms known as skin flora compete with the bad microorganisms for space and nutrients