infection and responce

• microorganisms that enter the body can cause communicable disease (infectious) plants, animals and humans can be infected by them
• three viral diseases?

  • measles
  • HIV
  • tobacco mosaic virus
• how is measles spread?

  measles is spread of droplets of liquid from sneezes or coughs.

  symptoms include a red rash on the skin and a fever

  can lead to pneumonia

  most people are vaccinated against it
• how is HIV spread?

  spread by sexual contact or exchanging bodily fluids, can be controlled by antiviral drugs, attack the cells in the immune system, can lead to AIDS
• effects of tobacco mosaic virus plants

  parts of the leaves become discoloured, affecting photosynthesis and plant growth.
• how does salmonella food poisoning work?

  caused by the salmonella bacteria, symptoms include fever, stomach cramps, vomiting and diarrhea, caused by toxins produced by the bacteria, most poultry in the UK vaccinated against it.
• how does gonorrhea work?

  sexually transmitted bacterial disease passed on my sexual contact, symptoms include pain when urinating and thick yellow/green discharge, treated with antibiotic and can be prevented by using barrier methods during sexual contact
• ways to prevent the spread of diseases

  • being hygienic ( e.g. washing hands)
  • destroying vectors
  • isolation
  • vaccination
• how is malaria spread?

  caused by a protist, transmitted bt mosquitoes, causes fever and can be fatal
• what is bacteria?

  small cells that reproduce quickly in the body, produce toxins that make you feel ill and damage cells and tissues
• what is a virus?

  much smaller than bacteria, reproduce quickly in the body, live inside other cells where they replicate and burst out to release the virus
• protists


  eukaryotes, some are parasites living on or inside other organisms, often carried by a vector
• fungi


  some single-celled, others have hyphae that grow and penetrate human skin and plant surfaces, produce spores for spreading
• how are pathogens spread?

  through water, air, direct contact including contaminated surfaces
• defence system

  • the skin acts as a barrier to pathogens
  • hairs (e.g. eyelashes)
  • mucus
  • ear wax
• defence system components

  • the skin acts as a barrier to pathogens
  • hair and mucus in the nose trap particles
  • trachea and bronchi secrete mucus to trap pathogens
  • stomach contains hydrochloric acid to kill pathogens
• white blood cells

  • phagocytosis engulf and digest pathogens
  • produce antitoxins to neutralise toxins
  • produce antibodies which lock onto antigens on pathogens surface
• vaccinations

  • injection of dead or weakened pathogen to produce antibodies -> these antibodies then remember these antibodies, so its easier to fight off the pathogen in the future
  • antibodies attack the pathogens upon reinfection
• developing drugs

  1. pre-clinical testing on human cells and tissues
  2. testing on living animals
  3. clinical testing on healthy human volunteers
  4. placebo and placebo effect
  5. blind and double blind trials
• painkillers


  relive pain and symptoms but do not tackle the cause
• antibiotics


  kill bacteria, not viruses
• drugs from plants

  • aspirin - willow tree
  • digitalis - foxglove
  • penicillin - mould (penicillium)