4.1 Communicable diseases

• What is pathogen?

  A microorganism that causes disease
• What are the effects of ring rot in plants? (caused by bacteria)

  • Infects vascular tissue causing leaf wilting
• How do viruses invade cells?

  They take over the genetic machinery of cells
• How do viruses replicate themselves?

  By using the genetic machinery of the host cell
• What are the methods of direct transmission of infections?

  • Inhalation (airborne infection)
  • Direct skin contact or fluid exchange
  • Penetrate skin actively (enzymes) or passively (wounds)
• What are the methods of indirect transmission of infections?

  • Via a vector
  • Spores
  • Consumption of contaminated food/drink
  • Inoculation through contaminated equipment
• What do physical defenses do against infections?

  Reduce infection by blocking entry
• How do chemical defences reduce infections?

  Reduce/prevent the growth of pathogens
• How do alkaloids affect animals?

  They taste bitter and deter feeding
• What do physical boundaries prevent?

  Pathogens from entering the plant
• What is the role of waxy cuticle in plants?

  It prevents pathogen entry
• What is the role of tannins in plant defense?

  They inhibit digestive enzymes in insects
• How do receptor molecules help plants?

  They allow recognition of pathogens
• What is the response of plants to infection?

  Rapid cell death around the infection site
• Why is necrosis important?

  It's the rapid death of tissue surrounding the infection site which prevents the pathogen from spreading
• How do chemical defences reduce infection?

  By producing toxic compounds
• What role does callose play in plant defence?

  It's deposited in the sieve tubes and prevents the flow of phloem sap (prevents pathogen from spreading)
• What is the role of skin in animal defence against infection?

  It acts as a physical barrier

  Salty residue from sweat creates an inhospitable environment for pathogens
• What is the function of hydrochloric acid in the stomach?

  It kills ingested bacteria
• What do hair and mucus do in the respiratory system?

  Trap pathogens
• What are expulsive reflexes in animal defense?

  They expel pathogens from the body
• What is the function of mucous membranes in animal defense?

  They trap and expel pathogens
• What is the role of blood clotting in animal defence?

  It prevents blood loss and infection of pathogen
• Role of inflammation as a primary non-specific defence

  • damaged vessels release histamines causing vasodilation
  • increases blood flow and permeability of blood vessels - causes swelling
  • cytokines are released and trigger an immune response
• What are the primary non-specific defences in animals?

  • Blood clotting
  • Wound repair
  • Inflammation
  • Expulsive reflexes
  • Mucous membranes
• What is a pathogen?

  Microorganism that causes disease
• What does reproductive hyphae do in fungi?

  Releases spores causing redness and irritation
• What are protoctista often known as?

  Parasites that live on or inside other organisms
• How are protoctista transferred?

  By vectors like mosquitoes
• What happens to the host cell during viral replication?

  It eventually bursts, releasing new viruses
• What are passive plant defenses?

  Always present physical and chemical barriers
• What do hydrolytic enzymes do in plant defenses?

  Break down cell walls of pathogens
• What are terpenoids and alkaloids in plants?

  Chemicals toxic to insects and fungi
• What is the role of receptors in plant defenses?

  Detect foreign organisms and trigger defenses
• What is callose deposition in plants?

  Blocks phloem flow to prevent pathogen spread
• What is the function of skin as a barrier to infection?

  Tough keratin layer acts as a waterproof barrier
• How does hydrochloric acid in the stomach protect against pathogens?

  Kills bacteria in consumed food
• What role do hair and mucus play in the nose?

  Trap pathogens and irritants
• What are expulsive reflexes in primary defenses?

  Coughing or sneezing to expel pathogens
• What is the function of blood clotting in defense?

  Prevents blood loss and entry of pathogens