Biology Chapter 3

• 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, kissing, contact with bodily fluids, microorganisms from faeces, infected plant material)
  • By water (drinking or coming into contact with dirty water)
  • By air (pathogens carried in droplets from sneezing, coughing or talking)
• Reducing the damage of disease to populations

  1. Improving hygiene (hand washing, using disinfectants, isolating raw meat, using tissues)

  2. Reducing contact with infected individuals

  3. Removing vectors (using pesticides/insecticides, removing habitat)

  4. Vaccination (injecting a small amount of a harmless pathogen to make the individual immune)
• Measles


  Viral disease with symptoms of fever and red skin rash, can lead to other problems like pneumonia, encephalitis and blindness
• HIV


  Viral disease that initially has flu-like symptoms, then attacks the immune system leading to AIDS
• Preventing the spread of HIV

  1. Using condoms, not sharing needles, screening blood, mothers with HIV bottle-feeding instead of breastfeeding

  2. Using antiretroviral drugs to stop the virus replicating
• Tobacco mosaic virus


  Plant pathogen that causes discolouration of leaves, reducing photosynthesis and yield
• Preventing the spread of tobacco mosaic virus


  Good field hygiene and pest control, growing TMV-resistant strains
• Salmonella food poisoning


  Bacterial disease with symptoms of fever, stomach cramps, vomiting, diarrhoea
• Preventing the spread of Salmonella

  Poultry vaccinated against Salmonella, keeping raw meat away from cooked food, avoiding washing raw meat, washing hands and surfaces, cooking food thoroughly
• Gonorrhoea


  Bacterial sexually transmitted disease with symptoms of thick yellow/green discharge and pain when urinating
• Preventing the spread of gonorrhoea

  Using contraception like condoms, using antibiotics (though resistant strains are developing)
• Rose black spot


  Fungal disease that causes purple/black spots on rose leaves, reducing photosynthesis and causing leaves to turn yellow and drop early
• Preventing the spread of rose black spot

  Using fungicides or stripping affected leaves and burning them
• Malaria


  Protist disease with symptoms of fevers and shaking when the protists burst out of blood cells
• Preventing the spread of malaria

  Using insecticide coated nets, removing stagnant water to prevent mosquito breeding, travellers taking antimalarial drugs
• Non-specific immune defences


  • Skin (physical barrier, antimicrobial secretions, skin flora)
  • Nose (hairs and mucus to prevent particles entering lungs)
  • Trachea and bronchi (mucus to trap pathogens, cilia to waft mucus upwards)
  • Stomach (hydrochloric acid to kill pathogens)
• Specific immune defences


  • Phagocytosis (white blood cells engulfing and consuming pathogens)
  • Producing antibodies (bind to pathogen antigens)
  • Producing antitoxins (neutralise pathogen toxins)
• Vaccination


  Injecting a dead or inactivated form of a pathogen to stimulate white blood cells to produce antibodies, providing immunity before infection
• How vaccination works


  1. The vaccine contains a dead or inactivated form of the pathogen

  2. This stimulates white blood cells to produce antibodies complementary to the pathogen antigens
• Advantages of vaccination


  • Eradicated many diseases, reduced occurrence of many
  • Can prevent epidemics through herd immunity
• Disadvantages of vaccination


  • Not always effective in providing immunity
  • Bad reactions (such as fevers) can occur
• Antibiotics


  Medicines that kill bacterial pathogens inside the body without damaging body cells
• Antibiotics cannot kill viruses as they use body cells to reproduce, meaning any drugs that target them would affect body tissue too
• Painkillers


  Only treat the symptoms of a disease, rather than the cause
• How antibiotics work


  1. Can be taken as a pill, syrup or directly into the bloodstream

  2. Different antibiotics are effective against different types of bacteria, so receiving the correct one is important

  3. Their use has decreased the number of deaths from bacterial diseases
• Penicillin


  Example of an antibiotic
• The great concern is that bacteria are becoming resistant to antibiotics
• How antibiotic resistance develops

  1. Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics

  2. When these bacteria are exposed to antibiotics, only the non-resistant ones die

  3. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases
• Preventing the development of antibiotic resistant strains

  1. Stop overusing antibiotics (unnecessarily exposing bacteria)

  2. Finishing courses of antibiotics to kill all bacteria
• Many drugs were initially discovered in natural sources
• 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)
• 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