Health and disease

• Pathogens


  Microorganisms that cause infectious disease, including viruses, bacteria, protists and 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
  • 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)
  • 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 (a common example is the droplet infection)
• Reducing the damage of disease to populations

  1. Improving hygiene

  2. Reducing contact with infected individuals

  3. Removing vectors

  4. Vaccination
• Vaccination


  Injecting a small amount of a harmless pathogen into an individual's body, so they can become immune to it and not get infected
• Herd immunity


  When a large proportion of the population is vaccinated, the spread of the pathogen is reduced as there are less people to catch the disease from
• Measles


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


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


  • Symptoms: Discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield
  • Spread by contact between diseased plants and healthy plants, insects act as vectors
  • Prevented by good field hygiene and pest control, growing TMV-resistant strains
• Salmonella food poisoning

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


  • Symptoms: Thick yellow or green discharge from the vagina or penis, pain when urinating
  • Spread through unprotected sexual contact
  • Prevented by using contraception such as condoms and antibiotics
• Rose black spot


  • Symptoms: Purple or black spots on leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early
  • Spread by the spores of the fungus in water or by wind
  • Prevented by using fungicides or stripping the plant of affected leaves
• Malaria

  • Symptoms: Fevers and shaking
  • Spread by the female Anopheles mosquito, in which the protists reproduce sexually
  • Prevented by using insecticide coated insect nets, removing stagnant water, and travellers taking antimalarial drugs
• Non-specific defence system

  1. The skin acts as a physical barrier, produces antimicrobial secretions, and has good microorganisms

  2. The nose has hairs and mucus to prevent particles entering the lungs

  3. The trachea and bronchi secrete mucus and have cilia to trap pathogens

  4. The stomach produces hydrochloric acid to kill pathogens
• Specific immune system

  White blood cells can phagocytose (engulf and consume) pathogens, produce antibodies that bind to pathogens, and produce antitoxins to neutralise toxins
• Antibodies

  Specific complementary antibodies are produced to bind to the antigens on the surface of pathogens
• Immunity

  If you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate, so the individual will not feel the symptoms of the illness
• Vaccination

  Involves making an individual immune to a certain disease by injecting a dead or inactivated form of the pathogen, which stimulates white blood cells to produce antibodies
• Antibiotics

  Medicines that kill bacterial pathogens inside the body, without damaging body cells. They cannot kill viruses.
• Painkillers

  Only treat the symptoms of the disease, rather than the cause
• Bacteria becoming resistant to antibiotics

  Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics, and these resistant bacteria survive and reproduce
• Preventing the development of resistant bacterial strains

  1. Stop overusing antibiotics

  2. Finishing courses of antibiotics to kill all of the bacteria
• Epidemics (lots of cases in an area) can be prevented through herd immunity
• Bad reactions (such as fevers) can occur in response to vaccines (although very rare)
• The great concern is that bacteria are becoming resistant to antibiotics
• Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics


  1. When these bacteria are exposed to antibiotics, only the non-resistant one die

  2. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases

  3. This means that antibiotics that were previously effective no longer work
• To prevent the development of these resistant strains

  • Stop overusing antibiotics- this unnecessarily exposes bacteria to the antibiotics
  • Finishing courses of antibiotics to kill all of the bacteria
• Toxicity

  How poisonous a drug is
• Efficacy


  How well a drug carries out its role
• Preclinical testing

  Using cells, tissues and live animals to test new drugs
• Clinical trials

  Using volunteers and patients to test new drugs
• New drugs today are mainly synthesised by chemists
• Plants


  • Aspirin (originates from willow)
  • Digitalis (originates from foxgloves)
• Discovery of Penicillin


  1. Alexander Fleming was growing bacteria on plates

  2. He found mould (Penicillium mould) on his culture plates, with clear rings around the mould indicating there was no longer any bacteria there

  3. He found that the mould was producing a substance called penicillin, which killed bacteria
• Placebo


  Appears to look like the drug but has no active ingredient so no effect
• Single-blind


  Only the doctor knows whether the patient is receiving the drug
• Double blind

  Neither the patient or doctor knows whether they are receiving the drug, removing any biases the doctor may have when they are recording the results