INFECTION AND RESPONSE

• Pathogen


  Microorganisms that enter the body and cause disease
• Communicable (infectious) diseases


  • Diseases that can easily spread
• Both plants and animals can be infected by pathogens
• Bacteria


  Very small living cells that can reproduce rapidly inside your body and produce toxins that damage your cells and tissues
• Viruses


  Tiny, not cells, live inside your cells and replicate using the cells' machinery, then the cell bursts releasing new viruses, causing cell damage
• Protists


  Single-celled eukaryotes, some are parasites that live on or inside other organisms and can be transferred by a vector
• Fungi


  • Some are single-celled, others have a body made up of hyphae that can grow and penetrate human skin and plant surfaces, causing disease, and produce spores that can spread
• Viral, Fungal and Protist Diseases

  • Measles
  • HIV
  • Tobacco mosaic virus
  • Rose black spot
  • Malaria
• Ways pathogens can be spread

  • Water
  • Air
  • Direct contact
• How viruses cause cell damage

  1. Viruses live inside cells and replicate using the cells' machinery

  2. The cell then bursts, releasing new viruses
• Measles


  • Viral disease
  • Spread by droplets from an infected person's sneeze or cough
  • Causes red skin rash and fever
  • Can lead to serious complications like pneumonia or encephalitis
  • Most people are vaccinated against it when young
• HIV


  • Virus spread by sexual contact or sharing needles
  • Initially causes flu-like symptoms
  • Can be controlled with antiretroviral drugs
  • Attacks immune cells
  • Late stage infection is known as AIDS
• Tobacco mosaic virus (TMV)


  • Virus that affects many plant species like tomatoes
  • Causes mosaic pattern on leaves
  • Affects plant growth by reducing photosynthesis
• Rose black spot


  • Fungus that causes purple/black spots on rose leaves
  • Leaves can turn yellow and drop off
  • Reduces photosynthesis and plant growth
  • Spreads through water or wind
  • Can be treated with fungicides and removing affected leaves
• Malaria


  • Caused by a protist
  • Part of life cycle takes place in mosquitoes which act as vectors
  • Causes repeating fever episodes
  • Can be fatal
  • Spread can be reduced by stopping mosquito breeding and using insecticides/nets
• Photosynthesis is important for plant growth because it produces glucose
• Bacterial Diseases


  • Salmonella
  • Gonorrhoea
• Salmonella


  • Bacteria that causes food poisoning
  • Symptoms include fever, stomach cramps, vomiting and diarrhoea
  • Caused by toxins produced by the bacteria
  • Can be contracted from contaminated food, e.g. undercooked chicken
  • Poultry is vaccinated against Salmonella in the UK
• Gonorrhoea


  • Sexually transmitted bacterial disease
  • Causes pain when urinating and discharge
  • Originally treated with penicillin but now strains are resistant
  • Can be prevented by using barrier contraception and treating infected individuals
• Ways to reduce/prevent disease spread

  • Being hygienic (e.g. handwashing)
  • Destroying vectors (e.g. killing insects)
  • Isolating infected individuals
  • Vaccination
• Human body's features for fighting disease

  • Skin acts as barrier and secretes antimicrobial substances
  • Hairs and mucus in nose trap particles
  • Trachea and bronchi secrete mucus and have cilia to trap pathogens
  • Stomach produces hydrochloric acid to kill pathogens
• Immune system


  System that attacks pathogens that make it into the body
• How immune system attacks pathogens

  1. White blood cells consume and digest pathogens (phagocytosis)

  2. White blood cells produce antibodies specific to pathogens

  3. White blood cells produce antitoxins to counteract toxins
• If you have low white blood cell levels, you'll be more susceptible to infections
• HIV attacks white blood cells and weakens the immune system
• Phagocytosis


  White blood cells engulfing and digesting foreign cells
• How trachea and bronchi are adapted to defend against pathogens

  • They secrete mucus to trap pathogens
  • They are lined with cilia that waft mucus up to be swallowed
• Vaccination


  Injecting small amounts of dead or inactive pathogens to stimulate antibody production
• How vaccinations work


  1. Injecting dead/inactive pathogens with antigens

  2. Body produces antibodies to attack them

  3. If live pathogens later appear, antibodies quickly attack and kill them
• Pros of vaccination


  • Helped control many communicable diseases
  • Can prevent epidemics if large percentage of population vaccinated
• Cons of vaccination


  • Vaccines don't always work
  • Can sometimes have bad reactions
• Deciding on vaccination requires balancing risks - risk of catching disease vs risk of bad reaction
• Basia is vaccinated against flu, Cassian isn't


  Basia doesn't fall ill when exposed to flu virus, Cassian does
• Painkillers


  Drugs that relieve pain, but don't tackle the cause of the disease or kill pathogens
• Antibiotics


  Drugs that kill or prevent the growth of bacteria causing the problem, without killing the body's own cells
• Antibiotics don't destroy viruses (e.g. flu or cold viruses)
• The use of antibiotics has greatly reduced the number of deaths from communicable diseases caused by bacteria
• Bacteria becoming resistant to antibiotics

  1. Bacteria mutate and become resistant

  2. Resistant bacteria survive and reproduce

  3. Resistant strain increases in population
• MRSA (meticillin-resistant Staphylococcus aureus) causes serious wound infections and is resistant to the powerful antibiotic meticillin
• Importance of avoiding over-prescribing antibiotics

  To slow down the rate of development of resistant strains