b3

• pathogen: microorganism that causes disease
• pathogen is spread through

  water droplets eg dirty water

  direct contact eg shaking hands, sex

  air eg coughing and sneezing
• pathogens can be reduced by good hygiene, disinfectants
• Bacteria - causes disease by dividing via binary fission and releasing toxins which make you feel ill
• bacteria

  salmonella

  • caused by undercooked foods
  • vomiting, diarrhoea
  • prevented by good food hygiene
  • unlikely to use antibiotics because it removed bacteria quickly through vomiting so isnt there long enough

  gonorrhoea

  • caused by sexual contact
  • green/yellow discharge, pain while urinating
  • prevented by condoms
• virus - causes disease by reproducing in body cells and exploding them

  • cannot use antibiotics because it cannot enter body cells without damaging it
• fungi - penetrate human skin and surface of plants
• fungi

  RBS:

  • spread by wind and water
  • black spots on leaves = less photosynthesis = stunted growth
  • prevented by destroying infectious plants and using fungicides
• protists - maybe parasites

  parasites - live in another organism and causes damage, transferred to other organisms by a vector which doesnt get the disease itself eg mosquito
• preventing disease

  • being hygienic eg washing hands
  • destroying vectors
  • isolating infected individuals
  • vaccinations

  scientists have not yet discovered how to cure viral diseases
• skin prevents pathogens from entering the body by

  • acting as a physical barrier
  • scab formation after a wound
  • secretes oils and antimicrobial substances that kill pathogens
• respiratory system prevents pathogens from entering the body by

  • nose - has hair and mucus which traps pathogens
  • trachea and bronchi - has mucus that traps pathogens, ciliated cells move mucus to the mouth so it can be swallowed
• stomach prevents pathogens from infection the body by

  • secreting hydrochloric acid which kills any pathogens present
• White blood cells

  • phagocytes - engulf and digest pathogens
  • b-lymphocytes (2nd line defence) - 1. send antibodies to antigen (complementary shape - only target one antigen) for a pathogen, 2. wait for phagocytes to engluf and digest it 3. produce memory cells which stay in the blood and reproduce antibodies quickly if the pathogen enters again
  • lack of WBCs = risk of infection, pathogen remains in the body
• edward jenner - discovery of vaccinations
• vaccinations

  • dead or weakened pathogen injected (it cannot reproduce)
  • b-lymphocytes send antibodies which are specific to the antigen of the pathogen
  • phagocytes engulf and digest
  • memory cells produced
• monoclonal antibodies - one type of antibody
• antitoxins bind to toxins released by pathogens to neutralise them
• monoclonal antibodies

  1. mouse is injected with specific pathogen
  2. in response, b-lymphocytes are produced which have specific antibodies for the antigen of the pathogen
  3. these are collected
  4. it is fused with a tumour cell because they clone quickly - they are called hybridoma
  5. hybridoma can clone antibodies quickly
  6. screened to make sure they are producing correctly
  7. more are clones
• uses of monoclonal antibodies

  • pregnancy tests

  1. pee on a stick where mobile antibodies bond to HCG hormone
  2. mobile antibody also has a blue bead attached
  3. test strip near end of stick has more mobile antibodies
  4. when pregnant, HCG hormone attaches to the blue bead and moves along the stick to the strip with the antibodies turning it blue
  5. if not pregnant, the blue bead has no hormones attached so moves up the stick but doesnt bind to the antibody
• teating diseases (monoclonal antibodies)

  cancer cells have antigens on their cell membranes called tumour markers (not found on normal body cells)

  1. Producing monoclonal antibodies specific to the tumour markers in order to stimulate the immune system to attack the cell.
  2. monoclonal antibodies bind to receptor sites on the cell surface membrane of the cancer cells. This means growth-stimulating molecules cannot bind, stopping the cell from dividing.
  3. monoclonal antibodies can attach to toxic drugs, chemicals or radioactive substances and transport them as they can only bind to cancer cells.
• herd immunity - when a large proportion of a population is immune to a disease so the spread of the pathogen is reduced as there are less people to catch the disease from
• advantages of vaccinations

  • eradicated many deadly diseases (eg chicken pox)
  • many epidemics prevented
  • herd immunity protects those without the vaccination

  disadvantages

  • not guaranteed to work
  • side effects such as fevers
• antibiotics can kill bacterial infections because it inhibits the synthesis of cell walls but not viral infections because viruses invade inside cells and antibiotics cannot enter cells without damaging it

  unlikely to use with salmonella because the bacteria is removed quickly via vomitting
• antibiotic resistance - mutations of bacteria are random and dangerous because they become resistant to the antibiotic. The antibiotic therefore cannot kill the bacteria, and the mutated bacteria survives and reproduces quickly passing on their alleles and creating a larger proportion of antibiotic resistant bacteria, the disease therefore cannot be cured

  to prevent this, it is prescribed less often and avoid overuse
• painkillers only treat the symptoms not kill the pathogen
• digitalis is extracted from foxglove to treat heart conditions
• asprin is extracted from willow bark - painkiller
• alexander flemming discovered penicilin from a type of mould that kills bacteria
• drug trials

  1. preclincal: tested on live animals, cells or tissue to test for toxicity
  2. clinal: low dose given to a healthy group of volunteers to test for side effects
  3. tested on a small number of those with the disease to test for optimum dosage
  4. double blind trial: half with a placebo and half with the drug (no one knows which is which) to check for efficacy and removes bias off the doctor
  5. peer reviewed to check for repeatability
• advantages of monoclonal antibodies

  • only bind to specific cells - healthy cells are not affected
  • can treat many conditions

  disadvantages:

  • expensive to develop
  • difficult to attach monoclonal antibodies to drugs
• non specific defence system

  • skin - acts as a protective barrier, has hair to trap pathogens
  • platelets clot open wounds and form scabs to prevent microbes from entering
  • respiratory system - nose contains hair to trap pathogens, trachea contains mucus to trap pathogens, trachea contains cillia to sweep mucus up the throat so pathogens enter digestive system
  • stomach contains hydrochloric acid to kill pathogens