3: infection

• What are the four types of pathogens?

  Virus, bacteria, fungi, protozoa
• What is a pathogen?

  A microorganism that causes infectious disease
• How can pathogens be spread?

  Direct contact

  Water

  Air

  Vectors
• What can bacteria produce?

  Poisons (toxins) that damage tissues and make us feel ill
• Where do viruses live and reproduce?

  Inside cells, which causes cell damage
• What is measles?

  -viral disease

  -causes fever and red skin rash

  -can be fatal

  -most young children are vaccinated

  -spread by droplets from coughs and sneezes
• What is HIV?

  -viral disease

  -causes flu symptoms

  -attacks immune cells

  -can be controlled with antiretroviral drugs

  -spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.

  
• What is AIDS?

  -caused by HIV

  -when the body's immune system becomes so badly damaged it can no longer deal with other infections
• What is TMV?

  -tobacco mosaic virus

  -viral infection

  -affects plants eg tomatoes

  -causes 'mosaic' discolouration on leaves

  -plant has reduced growth due to less photosynthesis

  
• What is Salmonella?

  -bacteria which release toxins

  -food poisoning

  -spread by bacteria ingested in food/on food prepared in unhygenic conditions

  -In the UK, poultry (chickens etc) are vaccinated against Salmonella to control the spread.

  -causes cramps, vomiting and diarrhoea
• What is gonorrhoea?

  -bacteria

  -STD (sexually transmitted disease)

  -causes a thick yellow or green discharge from the vagina or penis and pain on urinating

  -bacteria used to be easily treated with penicillin

  -now there are resistant strains, harder to treat

  -spread by sexual contact > prevent by using a barrier method of contraception, eg a condom
• What is rose black spot?

  -fungal disease

  -purple/black spots develop on leaves

  -leaves turn yellow and drop off

  -photosynthesis reduced -> less growth

  -treat with fungicides/removing and destroying affected leaves

  
• What is malaria?

  -protist

  -mosquitos are the vector (they carry the protist)

  -causes cycles of fever and can be fatal

  -spread prevented by using mosquito nets and preventing mosquitos from breeding
• What non-specific defences do humans have?

  -skin

  -nose (nose hairs)

  -trachea and bronchi (villi/mucus to remove pathogens)

  -stomach (Hydrochloric acid)
• What is phagocytosis?

  lymphocytes (white blood cells) engulf foreign cells (pathogen) and destroy them
• What is antitoxin production?

  Lymphocytes produce antitoxins to neutralise toxins produced by pathogens
• What are antibodies?

  -produced by lymphocytes

  -specific to one pathogen

  -bind to the pathogen
• What does vaccination involve?

  Introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate white blood cells to produce antibodies.

  
  

  If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection
• What are the two differences between the primary and secondary immune response?

  Secondary is faster

  Secondary produces more antibodies
• What are antibiotics?

  Medicines that help to cure bacterial disease by killing infective bacteria inside the body.

  Only work on bacteria

  Specific antibiotics work on specific bacteria

  Eg penicillin
• What has been a pro and a con of using antibiotics?

  + Reduced deaths from infectious bacterial diseases

  
  

  - Strains of bacteria that are resistant to antibiotics have emerged
• What are painkillers and what do they do?

  Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens.
• What is the problem with developing drugs to kill viruses?

  It is difficult to develop drugs that kill viruses without also damaging the body's tissues.
• Where does the heart drug digitalis originate from?

  Foxgloves plant
• Where does the painkiller aspirin originate from?

  Willow tree
• Where does penicillin originate from, and who discovered it?

  Penicillium mould

  Discovered by Alexander Fleming
• Where do most new drugs come from?

  -Synthesised by chemists in pharmaceutical industry

  -Starting point may still be chemicals from plants
• What are new drugs tested for?

  Toxicity, efficacy and dose
• What happens during drug clinical trials?

  -Clinical trials use healthy volunteers and patients.

  -Very low doses of the drug are given at the start of the clinical trial.

  -If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.
• What is a double blind trial?


  Where the patients AND researchers don't know if patients have the drug or placebo
• What is a placebo?

  A "fake" drug, often a sugar pill to see if improvements are psychological.
• [Triple only] What are monoclonal antibodies?


  Produced from a single clone of cells

  Specific to one binding site on one protein antigen

  Can target a specific chemical or specific cells in the body
• [Triple only] How are monoclonal antibodies produced?

  -A mouse is injected with a form of the pathogen to stimulate its lymphocytes to make a particular antibody.

  
  

  -The lymphocytes are combined with a tumour cell to make a hybridoma cell.

  
  

  -The hybridoma cell divides and makes the antibody.

  
  

  -Single hybridoma cells are cloned to produce many identical cells that all produce the same antibody.

  
  

  -A large amount of the antibody can be collected and purified.
• [Triple only] What are some uses of monoclonal antibodies?

  -for diagnosis such as in pregnancy tests

  
  

  -in laboratories to measure the levels of hormones and other chemicals in blood, or to detect pathogens

  
  

  -in research to locate or identify specific molecules in a cell or tissue by binding to them with a fluorescent dye

  
  

  -to treat some diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other cells in the body.
• [Triple only] Are monoclonal antibodies widely used and why?

  They are not yet as widely used as everyone hoped when they were developed

  
  

  They create more side effects than was expected
• [Triple only] How can plant diseases be detected?

  • stunted growth

  • spots on leaves

  • areas of decay (rot)

  • growths

  • malformed stems or leaves

  • discolouration

  • the presence of pests
• [Triple only] How can plant diseases be identified?

  • reference to a gardening manual or website

  • taking infected plants to a laboratory to identify the pathogen

  • using testing kits that contain monoclonal antibodies.
• [Triple only] What can plants be infected by?

  Viral, bacterial, fungal infections

  Insects
• [Triple only] How can plants be damaged by ion deficiency?

  • stunted growth caused by nitrate deficiency

  -nitrate ions are needed for protein synthesis/growth

  
  

  • chlorosis caused by magnesium deficiency

  -magnesium ions are needed to make chlorophyll
• [Triple only] What are some physical defence mechanisms of plants?

  • Cellulose cell walls.

  • Tough waxy cuticle on leaves.

  • Layers of dead cells around stems (bark on trees) which fall off.