Communicable diseases, disease prevention and immune system

• What are the two main ways of classifying bacteria

  • cell wall
  • shape
• What is Gram staining

  A process used to classify bacteria by their cell wall
• What is an antibiotic

  A compound that inhibits or kills bacterial growth
• What is a communicable disease

  A disease that can spread from one organism to another
• What is a vector

  Something that carries pathogens from one organism to another
• What is a bacteriophage

  A virus that attacks bacteria
• What is a parasite

  An organism that lives off a larger organism
• What are the two stains used for Gram staining

  • crystal violet
  • safranin
• What does a Gram positive bacteria look like under a microscope

  blue/purple -> absorbed crystal violet stain -> cell wall is made of peptidoglycan
• What does a Gram negative bacteria look like under a microscope

  red -> absorbed safranin stain -> cell wall made of peptidoglycan and lipopolysaccharide (an extra layer)
• What are the four main shapes of bacteria

  Cocci -> spherical

  Vibrio -> curved

  Bacilli -> rod shaped

  Spirilli -> spiral
• How do bacteria reproduce

  Binary fission:

  1 - duplication of chromosome

  2 - continued cell growth

  3 - division into two cells
• How do bacteria cause disease

  produce toxins -> damage cells -> can damage cell membrane, enzymes or genetic material
• What are the characteristics of tuberculosis

  • bacterial infection
  • damages and destroys lung tissue
  • suppresses immune system
  • curable through antibiotics
  • preventable through improved living standards and vaccination
• What are the characteristics of bacterial meningitis

  • bacterial infection
  • infects meninges of the brain (protective tissue)
  • can spread to rest of body -> causing septicemia and rapid death
  • mainly affects very young children and 15 - 19 year olds
  • creates a blotchy red/purple rash -> does not disappear with glass test
• What are the characteristics of ring rot

  • bacterial infection
  • damaged leaves, tubers and fruit
  • can destroy up to 80% of crop -> no cure
  • once infected -> field cannot be used for the following two years
• How do viruses invade cells to reproduce

  1 - virus attaches to chosen host cell

  2 - genetic material is injected into host cell

  3 - viral genes cause host cell to make new cells

  4 - host cell splits open, releasing new viruses
• What are the characteristics of HIV

  • viral infection
  • targets T-helper cells in immune system
  • gradually destroys immune system
  • spread through bodily fluids
  • no cure or vaccine -> antiretroviral drugs slow progression
• What are the characteristics of influenza

  • viral infection
  • kills ciliated epithelium cells in respiratory -> leaves airways open to secondary infection
  • 3 main strains
  • can be fatal (uncommon) -> most common amongst young children, old people and people with a chronic illness
• What are the characteristics of tobacco mosaic virus

  • viral infection
  • infects tobacco plants and 150+ other species
  • damages leaves, flowers and fruit -> stunts growth and reduced yield -> can lead to total crop loss
• What are the characteristics of cattle ringworm

  • fungal infection
  • causes grey-white, crusty, infectious, circular areas of skin
• What are the characteristics of athletes foot

  • fungal infection
  • grows on and digests warm, moist tissue between toes
  • causes cracking and scaling -> itchy and may become sore
• What are the characteristics of black sigtoka

  • fungal infection
  • found in banana plants
  • attacks and destroys leaves -> hyphae penetrate and digest cells -> turns leaves black
  • resistant strains are being developed
• What are the characteristics of blight in potatoes

  • caused by protists
  • hyphae penetrate host cells -> destroys leaves, tuber and fruit
  • no cure -> resistant strains, careful management and chemical treatments help reduces spread of infection
• What are the characteristics of malaria

  • caused by protists
  • spread through mosquito bites -> reproduce inside female mosquitoes -> female needs blood for her eggs -> infection is spread through the bite
  • invades red blood cells and can invade the brain
  • no vaccine and limited cures -> controlling vectors can help control infection rates -> preventative measures (eg mosquito nets)
• What are the key features of a protist

  • unicellular
  • has a nucleus
  • not classed as an animal OR a plant cell
• What are the forms of disease transmission between animals

  DIRECT TRANSMISSION:

  Direct contact (eg contact with bodily fluids / skin to skin)

  Inoculation (eg breaks in skin / sharing needles)

  Ingestion (eg taking in contaminated food/drink)

  INDIRECT TRANSMISSION:

  Fomites (inanimate objects eg bedding / socks)

  Droplet infection

  Vectors
• What are an animals non-specific defences against infection

  • inflammation
  • fever
  • phagocytes
• How does inflammation help prevent infection in animals

  • localised response
  • mast cell is activated in damaged tissue -> releases histamines and cytokines

  Histamines:

  • cause blood vessels to dilate -> localised heat and redness
  • make blood vessels more 'leaky' -> forces plasma out (becomes known as tissue fluid) -> causes swelling and pain

  Cytokines -> attract white blood cell
• How does a fever help prevent infection

  • a raised body temperature
  • higher temperatures can inhibit pathogen reproduction
  • specific immune system works best at higher temperatures
• How do phagocytes help prevent infection

  Specialised white blood cells that build up at site of infection and engulf pathogens
• What are the steps that phagocytes undergo to help prevent infection

  1 - Phagocyte is attracted to chemicals made by pathogens

  2 - Phagocyte recognises non-self proteins on pathogens

  3 - Phagocyte engulfs pathogens and encloses it in a phagosome (this is similar to a vacuole)

  4 - Phagosome combines with lysosome to form phagolysosome. Enzymes from the lysosome digest and destroy the pathogen

  5 - MHC/antigen complex is displayed on phagocyte membrane, making it an antigen presenting cell
• What is clonal selection

  Selecting the correct antibody for cloning
• What are the types of B-cells

  Plasma cells

  B-effector cells

  B-memory cells
• What are the key features of plasma cells

  Only live for a few days

  produce and release antibodies into circulation -> can produce up to 2000 antibodies per second
• What are the key features of B-effector cells

  divide to form plasma cells
• What is CD4

  A protein present on the surface of T cells
• What are the four types of T cell

  Killer

  Helper

  Memory

  Regulator
• What is the main use for CD4

  Binds to surface antigens on antigen presenting cells (APC)
• How do killer T cells work

  Produce perforins -> makes holes in membranes -> makes it permeable