topic 3 infection and response

• Pathogens


  Microorganisms that cause infectious disease, including viruses, bacteria, protists, and fungi
• Types of pathogens


  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Viruses


  • Very small
  • Move into cells and use the biochemistry to make copies
  • Cause cell bursting and release copies into bloodstream
  • Damage and destroy cells, making individuals feel ill
• Bacteria


  • Small
  • Multiply quickly through binary fission
  • Produce toxins that can damage cells
• Protists


  • Some are parasitic, using humans and animals as hosts
• Fungi


  • Can be single-celled or have a body made of hyphae
  • Can produce spores that spread to other organisms
• Ways pathogens are spread

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


  • Kissing
  • Contact with bodily fluids
  • Direct skin to skin
  • Microorganisms from faeces
  • Infected plant material left in field
• Droplet infection


  Pathogens expelled in droplets when sneezing, coughing, or talking
• The damage that disease causes to populations can be reduced by limiting the spread of the pathogens
• Ways to limit the spread of pathogens

  • 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
• Vaccination


  • Injecting a small amount of a harmless pathogen to become immune
• Viruses are particularly dangerous as they can enter all types of cells, and scientists are yet to develop medicines to cure them
• Viral diseases


  • Measles
  • HIV
  • Tobacco mosaic virus
• Measles


  • Symptoms: Fever and red skin rash
  • Can lead to pneumonia, encephalitis, and blindness
  • Spread by droplet infection
  • Prevented by vaccinations for young children
• HIV


  • Symptoms: Initially flu-like, then attacks immune system leading to AIDS
  • Spread by sexual contact or exchange of bodily fluids
  • Prevented by using condoms, not sharing needles, screening blood, and antiretroviral drugs
• Tobacco mosaic virus


  • Symptoms: Discolouration of leaves, reduced yield
  • Spread by contact between diseased and healthy plants, insects as vectors
  • Prevented by good field hygiene and pest control
• Bacterial diseases


  • Salmonella food poisoning
  • Gonorrhoea
• Salmonella food poisoning


  • Symptoms: Fever, stomach cramps, vomiting, diarrhoea
  • Spread by raw meat and eggs, unhygienic conditions
  • Prevented by vaccinating poultry, keeping raw meat away from cooked food, washing hands and surfaces
• Gonorrhoea


  • Symptoms: Thick yellow or green discharge, pain when urinating
  • Spread through unprotected sexual contact
  • Prevented by using contraception and antibiotics
• Fungal diseases


  • Rose black spot
• Rose black spot


  • Symptoms: Purple or black spots on leaves, reduces photosynthesis
  • Spread by water or wind
  • Prevented by using fungicides or stripping affected leaves
• Protist diseases


  • Malaria
• Malaria


  • Symptoms: Fevers and shaking
  • Spread by female Anopheles mosquito
  • Prevented by insecticide nets, removing stagnant water, antimalarial drugs
• Non-specific defence system


  • Prevents pathogens from entering the body
• Components of the non-specific defence system

  • Skin
  • Nose
  • Trachea and bronchi
  • Stomach
• Skin


  • Acts as a physical barrier
  • Produces antimicrobial secretions
  • Skin flora compete with bad microorganisms
• Nose


  • Has hairs and mucus to prevent particles from entering lungs
• Trachea and bronchi


  • Secrete mucus to trap pathogens
  • Cilia waft mucus upwards to be swallowed
• Stomach


  • Produces hydrochloric acid to kill pathogens
• Specific immune system


  • Destroys pathogens that pass through non-specific system
• Modes of action of white blood cells

  • Phagocytosis
  • Producing antibodies
  • Producing antitoxins
• Phagocytosis


  • Engulfs and consumes pathogens, destroying them
• Producing antibodies


  • Each pathogen has an antigen, antibodies bind to them, clumping pathogens for easier identification
• Producing antitoxins


  • Neutralises toxins released by pathogens
• Vaccination


  • Makes individuals immune to a disease before infection
  • Immunising a large population reduces spread (herd immunity)
• Vaccine


  • Contains a dead or inactivated form of the pathogen
  • Stimulates white blood cells to produce antibodies
• Antibiotics


  • Kills bacterial pathogens without damaging body cells
  • Cannot kill viruses
  • Example: Penicillin
• Painkillers


  • Treat symptoms of disease, not the cause