Infection and response

• Pathogen


  A microorganism that causes disease
• Main types of pathogen

  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Bacteria

  • Salmonella (in animals)
  • Agrobacterium (in plants)
• Fungi


  • Athlete's Foot (in animals)
  • Rose black spot (in plants)
• Pathogen life cycle


  1. Infect a host

  2. Replicate and reproduce themselves

  3. Spread from their host and infect other organisms
• Pathogens


  • Have structural adaptations that make them successful at completing their life cycles and enable them to cause further disease
• Communicable diseases


  Diseases caused by pathogens that can be transmitted from one person to another or from organism to organism
• There are other types of disease which cannot be caught, such as inherited disorders like cystic fibrosis and deficiency diseases caused by lack of vitamins/minerals
• Diseases like cancer develop naturally due to carcinogens (chemical or other agents that cause cancer) or due to cell division occurring incorrectly
• All organisms, even bacteria, are affected by pathogens, but only some infections can be transferred to other organisms
• Ways pathogens can spread

  • Direct contact (e.g. shaking hands, sexual intercourse)
  • Water (e.g. dirty water transmitting cholera)
  • Air (e.g. coughs/sneezes spreading virus droplets)
  • Unhygienic food preparation (e.g. undercooked/reheated food causing E. coli food poisoning)
  • Vector (an organism that can transmit disease)
• White blood cells help destroy pathogens.
• Phagocytosis

  White Blood cells digest and engulf pathogens
• White blood cells make specific antibodies
• Antibodies attach to a pathogen and clump them together so more white blood cells can engulf more at once
• White blood cells produce anti-toxins to neutralise toxins
• Lymphocytes are the white blood cells involved in the specific immune response. They produce antibodies that respond to specific antigens on the surface of pathogens. Memory cells remain in the blood stream and lead to a quicker and stronger defence against a secondary infection by the same pathogen
• External protection against pathogen


  Nose

  Trachea

  Stomach

  Skin
• Nose


  Mucus traps pathogens
• Trachea and bronchi 


  Cilia wafts mucus up for you to swallow and go down into stomach
• Stomach 


  Acid kills the pathogens
• Skin 


  Scabs form a tough layer of defence