BIOLOGY TOPIC 3 - INFECTION AND RESPONSE

• what is a pathogen?

  microorganism that causes disease
• how do fungi make us ill?


  hyphae produce spores
• what type of disease is measles?

  how is it spread?


  virus

  spread by droplets from coughs and sneezes
• how is salmonella spread?

  bacteria on/in food
• how is HIV spread?

  how can the virus be controlled?

  exchange of bodily fluids

  controlled by antiretroviral drugs in early stages
• how is gonorrhoea controlled?

  barrier contraception
• how is rose black spot spread?

  water and wind
• how is the spread of malaria controlled?

  control of vectors

  use of mosquito nets
• methods used by white blood cells to destroy pathogens

  phagocytosis

  antibodies

  antitoxins
• how does the stomach defend against pathogens?

  hydrochloric acid kills pathogens
• how do tears help us to defend against pathogens?

  contain enzymes that destroy any pathogens that come in contact with our eyes
• how does mucus help to defend against pathogens?

  traps particles and bacteria entering our airways
• how do antibodies destroy pathogens?


  -WBCs recognise foreign antigens on surface of pathogens and produce protein molecules called antibodies

  -the shape of the antibody is complementary to the shape of the pathogen and lock on to the pathogen

  -causing microorganisms to cluster, allowing WBCs to come and digest them through phagocytosis
• what is the process of vaccination?


  -inject small amount of dead/inactive pathogen into blood

  -WBCs recognise the antigen is foreign and produce antibodies against it

  -some WBCs remain in blood as memory cells, so if infected by pathogen they are able to produce antibodies faster

  -if same pathogen infects the vaccinated person, then the immune system will destroy it before it causes illness
• herd immunity


  vaccinating a large proportion of a population, making it harder for pathogen to spread
• ways to prevent antibiotic resistance


  only prescribe when needed (not for minor or viral infections)

  patients should complete the course of antibiotics
• how does antibiotic resistance work?

  -random mutations within a population of bacteria

  -mutated bacteria are resistant to antibiotics, so survive

  -resistant bacteria reproduce, producing genetically identical copies, all resistant to antibiotics
• where does the heart drug digitalis originate from?


  foxgloves
• where does aspirin originate from?

  willow
• what is tested during drug test trials?

  dosage size

  toxicity

  efficacy
• preclinical testing


  first stage of testing

  -testing on human tissue and live animals

  -used to work out toxicity of drugs
• clinical testing


  second stage of testing

  -trials that involve testing drugs on healthy volunteers and patients to check that they're safe

  -if drug is safe, then further trials are done to work out dosage size
• placebo


  alternative that doesn't contain the drug
• double blind trial


  neither doctors or patients know who receives placebo or drug
• how are monoclonal antibodies produced?

  -antigen is injected into a mouse

  -mouse produces lymphocytes, producing antibodies specific to antigen

  -spleen cells which produce the lymphocytes are removed from mouse in surgery

  -spleen cells are fused with human white blood cells called myeloma cells to form hybridoma cells which divide indefinitely

  -hybridoma cells divide and produce millions of monoclonal antibodies specific to the original antigen
• uses of monoclonal antibodies

  pregnancy tests

  identifying chemicals in blood

  treating diseases
• magnesium deficiency in plants

  plant can't photosynthesise well so can't produce glucose needed for growth

  symptom = yellow leaves
• nitrate deficiency in plants


  nitrates are needed for production and synthesis of protein

  causes stunted growth
• plant defences


  bark = physical barrier

  thorns - stop animals eating them

  production of poisons to deter herbivores from eating
• signs of plant disease

  stunted growth

  discolouration

  decay

  spots on leaves
• ways to identify plant disease

  testing kits containing monoclonal antibodies

  gardening manual

  testing in laboratory
• explain how a vaccine for HIV could work to prevent a person from developing HIV infection 


  inactive HIV is injected into bloodstream

  white bloods cells produce antibodies

  specific antibodies are produced quickly

  antibodies destroy HIV
• describe the monoclonal antibody for HIV can be produced 


  HIV injected into mouse

  collect lymphocytes that make a specific antibody to HIV

  lymphocytes are combined with a tumour cell to create a hybridoma

  hybridoma cloned to create many cells that produce the antibody