Biology : Topic 10

• Pathogen


  Disease-causing organism
• Transmissible disease


  Disease in which pathogen can be passed from one host to another
• Incubation period


  The time when a pathogen is inside the body and starts to multiply and increase in number before you start to feel ill
• Methods of microbes' transmission

  1. Direct Transmission

  2. Indirect Transmission
• Direct Transmission


  • Host —> Host
• Indirect Transmission


  • Host —> vector —> host
• Indirect Transmission


  • Animal vectors
  • Food / water borne
• Body defense mechanisms


  • Mechanical Barriers
  • Chemical Barriers
• Mechanical Barriers


  • The dead outer layer of skin cells is a barrier
  • Oil glands in your skin makes antiseptic oil that kill pathogen
  • Blood clot prevents entry of microbes
  • Nose hairs filter the air and act as a barrier for microbes
• Chemical Barriers


  • Stomach acid kills the pathogen in your food
  • Mucous in your air passages sticks the dust and microbes
  • Cilia sweep mucous, dust and microbes up to your throat to be swallowed
  • Tears contain lysozyme enzyme that kills pathogen
• Second line of defense

  • Phagocytes engulf pathogens and destroy them
  • Lymphocytes produce antibodies and memory cells
• Antibodies


  Break down bacterial cell wall