Topic 3: infection and response

• Viruses

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


  • Small
  • They 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

  • They can either 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

  1. Direct contact-touching contaminated surfaces

  2. By water- drinking or coming into contact with dirty water

  3. 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)
• Direct contact

  • kissing, contact with bodily fluids, direct skin to skin, microorganisms from faeces, infected plant material left in field
• Droplet infection

  When sneezing, coughing or talking expels pathogens in droplets which can be breathed in
• Ways to reduce the damage of disease 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 to it so it will not infect them. This means they cannot pass it on.
• Bacteria


  Produces toxins inside the body
• Toxins produced by bacteria

  • Damage tissue
  • Make us feel ill
• Viruses

  Live and reproduce in cells, causing cell damage
• Measles

  A contagious viral disease
• Measles symptoms

  • Fever
  • Red skin rash
  • Can lead to pneumonia (lung infection)
  • Can lead to encephalitis (brain infection)
  • Can lead to blindness
• How measles is spread

  Droplet infection
• How measles is being prevented

  Vaccinations for young children to reduce transmission
• How HIV is spread

  • Sexual contact
  • Exchange of body fluids (e.g. blood from sharing needles)
• What happens when HIV enters the body

  1. Initially causes flu-like illness

  2. Enters lymph nodes

  3. Attacks body's own immune cells
• AIDS

  Life-threatening infections that can happen when a person's immune system has been badly damaged by HIV
• HIV

  Causes AIDS
• TMV (Tobacco mosaic virus)

  A pathogen that affects plants, such as tomatoes
• Tobacco mosaic virus (TMV)

  • Causes a unique 'mosaic' pattern of discolouration in the affected plant
  • Stunts the growth of the affected plant
  • Prevents photosynthesis from taking place
• Salmonella

  Bacteria that causes food poisoning if food has not been cooked properly or has been prepared in unhygienic conditions
• Salmonella food poisoning

  1. Bacteria releases toxins (poisons)

  2. Causes fever, stomach pain, vomiting and diarrhoea
• Gonorrhoea

  Sexually transmitted disease
• Gonorrhoea

  • Caused by bacterium
  • Was easily treated with penicillin until many resistant strains appeared
• Barrier methods of contraception

  • Can be used to stop the bacteria spreading from person to person
• Rose black spot

  A disease that affects rose plants
• How rose black spot is spread

  1. In water

  2. In the air (wind)
• Symptoms of rose black spot

  • Purple or black spots on the leaves
  • Leaves discolour and fall off
  • Makes it harder for plants to photosynthesise
  • Plant growth slows
• Treating rose black spot

  1. Removing and destroying discoloured leaves

  2. Using fungicides
• Malaria


  A disease spread by the female anopheles mosquito (a vector)
• How malaria is spread

  Mosquito carrying malaria transfers the infection into a person's bloodstream when it bites them
• Malaria


  • Leads to recurring and severe fevers, which can cause death
• 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
• Nonspecific defense system


  The body's first line of defense against pathogens, preventing them from entering the body
• Parts of the nonspecific defense system


  • Skin
  • Nose and mucus
  • Cilia in trachea and bronchi
  • Stomach acid
• Skin


  • Forms a protective layer covering the body
  • Outer layer of dead cells difficult for pathogens to penetrate
  • Produces sebum which can kill bacteria
  • Can scab over when damaged to prevent pathogen entry
• Nose and mucus


  • Contract pathogens before they enter the breathing system
• Cilia in trachea and bronchi

  • Covered in mucus which contract pathogens upwards towards the throat to be swallowed
• Stomach acid


  • Kills pathogens before they can make their way further down the digestive system