infection and response

• viruses are very small, they can move into cells where it uses their biochemistry to make copies of itself which leads to the cell bursting and releasing copies into blood stream.
• bacteria is small and multiply very quickly through binary fission, they produce toxins which damage cells.
• some protists are parasitic, meaning they use humans and animals as hosts as they live inside.
• fungi can be either single celled or have a body made of hyphae, they can produce spores which can spread to other organisms.
• Symptoms of HIV:

  • initially flu-like symptoms
  • then virus attacks immune system and leads to aids
  • causes body to be susceptible to many diseases.
• symptoms of measles:

  • fever
  • red skin rash
  • sometimes pneumonia
  • sometimes encephalitis (brain infection)
  • sometimes blindness
• symptoms of tobacco mosaic virus:

  • discolouration of the leaves
  • affected part of leaf cannot photosynthesis so less energy produced
• symptoms of salmonella:

  • fever
  • stomach cramps
  • vomiting
  • diarrhoea
• symptoms of gonorrhoea:

  • thick yellow or green discharge from vagina or penis
  • pain when urinating
• symptoms of rose black spot:

  • purple or black spots in leaves of rose plants
  • reduces area of leaf available for photosynthesis
  • leaves turn yellow and drop early
• symptoms of malaria:

  • fevers
  • shaking (when the protists burst out of blood cells)
• how bacterial diseases are prevented:

  • salmonella: vaccinate poultry, keeping raw meet separate, wash hands and surfaces after handling and cooking thoroughly.
  • gonorrhea: contraception like condoms, antibiotics (often used with penicillin due to resistant strains)
• how viral diseases are prevented:

  • measles: vaccination in children
  • HIV: using condoms, not sharing needles, screening blood for transfusion, mothers with HIV bottle feeding and antiretroviral drugs
  • TMV: good field hygiene and pest control, growing TMV resistant strains
• how is rose black spot prevented:

  using fungicides or stripping the plant of diseased leaves (must be burnt).
• how is malaria being prevented:

  using insecticide coated insect nests during sleep, removing stagnant water to prevent vector breeding, travellers taking antimalarial drugs to kill parasites entering the blood.
• the skin (non-specific) acts as a physical barrier, produces antimicrobial secretions and good microorganisms known as skin flora compete with the bad ones for nutrients and space.
• vaccines contain a dead or inactivated form of the pathogen, this stimulates the white blood cells to produce antibodies complementary to the antigens on the pathogen
• how can bacteria become antibiotic resident?

  due to mutations that occur during reproduction which result in certain bacteria no longer being killed
• examples of drugs originating from plants:

  • aspirin as a painkiller (from willow)
  • digitalis to treat heart problems (from foxgloves)
• symptoms of plant diseases:

  • stunted growth: nitrate deficiency
  • spots on leaves: rose black spot
  • areas of decay: rose black spot, potato blights
  • abnormal growth: crown galls due to bacterial infection
  • malformed stems or leaves: aphid infestation
  • discolouration: magnesium deficiency or tobacco mosaic virus
  • pests: caterpillars etc
• how do you identify plant disease?

  • garden manual
  • observing infected plant in a lab
  • using monoclonal antibodies in testing
• what can magnesium deficiency cause?

  chlorosis
• what is chlorosis?

  1. magnesium is needed to make chlorophyll
  2. this is vital for photosynthesis
  3. if less is being made then parts of the leaves appear green and yellow (chlorosis)
• what can nitrate deficiency cause?

  stunted growth
• how does a nitrate deficiency cause stunted growth?

  • nitrates in the soil convert sugars made in photosynthesis into proteins
  • these proteins are needed for growth
• what are a plants physical defences against the invasion of micro-organisms?

  • tough waxy cuticle stops entry into leaves
  • cellulose cell walls form a physical barrier into the cells
  • plants have layers of dead cells around stems to stop pathogens entering, the cells fall off with the pathogen
• what are a plants chemical defences to deter predators?

  • poisons to deter herbivores
  • antibacterial compounds kill bacteria (witch hazel)
• explain phagocytosis?

  1. phagocytes engulf and digest pathogens
  2. this can be non-specific or aided by antibodies which cause clumping of pathogens
  3. this can allow other white blood cells to produce the needed antibody
• production of antibodies:

  1. lymphocytes produce antibodies (each lymphocyte produce one type of antibody)
  2. they are Y-shaped proteins
  3. an antibody is complementary to the antigens on the surface of the pathogen
  4. it can take a few days to produce the antibodies specific to a pathogen which can give the infection enough time to make you feel unwell
• what are memory cells?

  • they are lymphocytes that remain in the body after an initial infection with a particular pathogen, which produce specific antibodies
  • if you get infected by the same pathogen with the same antigens, you can produce antibodies quicker before it can cause damage to the bodies tissues
• production of antitoxins

  • lymphocytes can produce antitoxins to deter toxins produced by pathogens
  • the antitoxins neutralise the effects of the toxin
• how does vaccination work?

  • exposing an individual to the antigens of a pathogen in an inactive or dead form
  • triggering an immune response
  • this results in the formation of memory cells which can make antibodies against it if infection reoccurs
  • they can destroy the pathogen before becoming infectious
  • consequently reduce the likelihood of the spread of infection
• what does herd immunity mean?

  if a large number of the population are vaccinated, it is unlikely that an unvaccinated individual will become infected with the pathogen
• how can we prevent the development of antibiotic resistant strains?

  1. stop overusing antibiotics- this unnecessarily exposes bacteria to antibiotics
  2. finishing courses of bacteria to kill all of the bacteria
• what are a plants mechanical defences?

  • thorns and hairs make it painful for animals to eat
  • some leaves droop or curl to move insects off
  • mimicry to trick animals (patterns, appearance and mimicking unhealthy traits)