disease

• Pathogens


  organisms that cause disease
• infectious disease (communicable)


  a disease caused by a pathogenwhich can spread from person to person
• non-infectious disease (non-communicable)


  not caused by pathogenic organisms influenced by genetic or lifestyle
• Types of pathogens


  - Bacteria

  - Viruses

  - Fungi

  - Protoctist
• Tuberculosis (TB) : Bacteria


  - causes : suppress immune system

  - organism : mammals

  - transmission : inhaling droplets

  - treatment : good sanitation and antibiotics
• Ringrot : Bacteria


  - causes : damages leaves, tuber and fruits

  - organism : potatoes, aubergines

  - transmission : direct contact (water)
• HIV / AIDs : Virus

  - causes : target T helps cells > destroys immune system

  - organism : humans and primates

  - transmission : bodily fluids
• Influenza : Virus


  - causes : kills ciliated epithelium cells > airway open to secondary infection like pneumonia

  - organism : mammals

  - transmission : inhaled droplets
• Tobacco Mosaic Virus


  - causes : damages leaves (brown spots), stunted growth, reduced yield

  - organism : plants

  - transmission : direct contact
• malaria : protoctist


  - organism : mammals

  - transmission : female anopheles mosquitoes

  - treatment : mosquitoes nets, infection/tablets
• Potato/tomato late blight : protoctista


  - causes : destroys leaves ( affects photosynthesis )

  - organism : tomatoes and potatoes

  - transmission : hyphae penetrate host cells in wind (direct contact)
• Black Sigatoka : fungus


  - causes : turns leaves black

  - organism : banana plants

  - transmission : spores in the wind (direct contact)
• athletes foot


  - causes : rash

  - organism : mammals

  - transmission : direct contact with contaminated surfaces
• How can communicable diseases be spread?

  direct and indirect transmission
• factors that affect transmission of communicable disease

  - social factors

  - living condition

  -climate
• example of social factors


  HIV undiagnosed in countries with reduced healthcare access
• example of living conditions

  overcrowding increases spread of diseases
• example of climate


  tropical countries ideal for mosquitoes to breed
• defensive barriers


  - mucus membrane

  - skin

  - blood clot

  - tranches

  - stomach hydrochloric acid

  - harmless bacteria

  - inflammation

  - expulsive reflexes
• mucus membrane


  contain lysozymes > kill bacteria by damaging its cell walls
• skin


  - stops pathogens getting inside

  - repaired outer layer

  - cell dividing and migrating of the edges of the wound

  - collagen fibres
• blood clots


  when blood vessels are damaged

  - prevents entry of pathogens and blood loss
• tracheal cartilage


  - contains goblet cells > secrete mucus > trap pathogens

  - ciliated epithelial cells > sweeps mucus towards stomach
• stomach


  contains hydrochloric acid > denature proteins and kills pathogens ingested in our food and drinks
• harmless bacteria


  - on skin and inside intestines

  - compete with any pathogenic organisms and reduce their ability to grow
• imflammation


  - occurs when tissue is damaged

  - helps isolate pathogens that have entered damaged tissue

  - vasodilation increases blood flow to the area > helps white blood cells to the site of damage
• Expulsive reflexes


  coughing and sneezing helps expel pathogens from the body
• 2 plant defences against pathogens

  physical and chemical
• physical defenses


  - waxy cuticle on leaf surface

  - cell wall

  - deposit polysaccharide called callose between cell wall and plasma membrane
• chemical defenses


  - produce antibiotic or fungicidal compounds > inhibited by growth of bacteria and fungi

  - produce insecticides > reduce risk of infection by plant virus by vectors
• antigens


  molecules of pathogen cell surface that trigger an immune response when detected by our immune system
• stages after detecting antigen

  - phagocytosis of pathogen

  - activation of T lymphocytes

  - activation of B lymphocytes

  - production of antibodies by plasma cells
• phagocytosis


  type of white blood cell which can destroy pathogens
• types of phagocytes


  - macrophages

  - monocytes

  - neutrophils
• Stages of phagocytosis


  - detect pathogen when receptors on its cell surface binds to the antigens on the pathogen

  - phagocyte wraps its cytoplasm around pathogen and engulfs it

  -pathogens in phagosomes and lysosome vesicles

  - vesicle lysosomes contain digestive enzymes that fuse with phagosome to form phagolysosome

  - digested pathogen removed by exocytosis but keep some antigen molecules on there cell surface > to alert other cells of foreign antigen

  - phagocyte is now referred to as antigen-presenting cell (APC)
• T lymphocytes (T cells)


  white blood cells with receptors on their surface
• clonal selection and clonal expansion

  - T cell binds to complementary antigen and activates

  - Then divides by mitosis to produce clones
• 4 types of T cells

  - T helper cells

  - T killer cells (cytotoxic T cells)

  - T regulatory cells

  - T memory cells
• T helper cells


  release chemicals to activate B lymphocytes
• T killer cells (cytotoxic T cells)


  destroy any cells which have been infected with the pathogen