pathogens

• communicable disease 


  caused by infective organisms called pathogens, can be passed from one individual to another.
• pathogen 


  infective micro-organism
• vectors

  carry pathogens from one organism to another
• bacteria

  = produce toxins that poison or damage the host cell causing disease, some break down the cell membrane, inactive enzymes interfere with genetic material so cells can't divide.

  • prokaryotes, no membrane bound organelles
  • cell wall made from peptidoglycan, DNA in plasmids.
  • classified by basic shape: bacilli (rod shape), cocci (spherical), vibrios (comma), spirilla (spiralled), spirachaelos (corkscrew)
  • or their walls: gram positive= purple/blue under microscope, gram negative= appear red
  • useful as the type of cell wall affects how bacteria react to different antibiotics.
• viruses

  =non-living infectious agents

  • parasites= feed/live inside another organism and cause it harm.
  • have complementary antigens to host receptors
  • reproduce rapidly and evolve by developing adaptations to their host.
  • bacteriophages= take over bacteria cells and use them to replicate, destroying them at the same time.
  • take over cell metabolism, the viral genetic material gets into the host cell and is inserted into host DNA. Viruses use host cells to make new viruses which then burst out the cell, destroying it.
• fungi

  = produce toxins which affect the host cells and cause disease some digest living cells and destroy them. Fungi affecting leaves stop them photosynthesising so can quickly kill the plant.

  • cell wall made of chitin
  • saprophyric fungi= feed on dead+ decaying matter.
  • pathogenic fungi= cause disease+ feed on living plant and animals.
  • when fungi reproduce they produce millions of tiny spores which can spread huge distances, this means they can spread rapidly and widely through crop plants.
• protists

  = take over cells and break them open as new generations emerge. They digest and use cell contents as they reproduce.

  • have a nucleus, are parasites, use people and animals as their host organism
  • need a vector to transfer them to host eg: malaria
  • or they enter the body directly through polluted water