communicable diseases

• Pathogen


  a microorganism that causes a disease
• Types of pathogen

  viruses, bacteria, fungi, protoctista
• How do viruses work?

  they take over cell metabolism and reproduce within body cells. they then burst out, destroying the cell.
• Examples of viruses in animals

  HIV/AIDS, flu, Covid 19
• How do bacteria work?

  cause disease by damaging cells or by releasing toxic waste products. this may breakdown cell surface membrane or inactivate enzymes
• examples of bacteria in animals

  Meningitis, tuberculosis
• How does fungi work

  sends out reproductive hyphae (mycellium) which release spores which causes redness and irritation. they may produce toxins
• examples of fungi in humans

  ringworm, athletes foot
• how does protoctista work


  may grow inside cells, feeding on the contents, damaging them
• examples of protoctista in animals

  malaria, dysentry
• how do viruses effect plants

  damages leaves, flowers and fruit. causes reduced yield
• examples of plant viruses

  tobacco mosaic virus
• how does bacteria effect plants

  cause blackening and death of vascular tissue- damaging leaves, tubers and fruit
• examples of plant bacteria

  ring rot
• how does fungi effect plants

  releases cellulases to digest and decay surrounding tissues causing mottled leaves and black fruit
• examples of plant fungi

  black sigatoka
• how does protoctista effect plants

  damages leaves, fruit and tubers
• examples of plant protoctista

  tomato and potato late blight
• direct transmission


  passing a pathogen host to host with no intermediary
• indirect transmission 


  passing a pathogen using a vector
• vector

  an organism that carries a pathogen from one host to another
• factors that increase risk of direct transmission

  overcrowding, poor ventilation, homelessness, poor diet, poor sanitation, poor health/immune system
• direct transmission in plants 


  via damaged roots, fungi spores in air or returned to soil by infected seed/fruit/leaf
• indirect transmission in plants

  insect transmission e.g dutch elm disease carried by beetle
• how does climate affect disease

  greater variety of pathogens found in warmer climates as pathogens can reproduce more rapidly
• passive defense 


  prevent entry of microbes
• active defence


  after the pathogen has been detected
• physical defenses

  cellulose cell wall, lignin, waxy cuticle, bark, stomatal closure, callose and tylose
• callose


  a large polysaccharide deposit that blocks phloem sieve tubes
• tylose


  balloon like swelling that blocks xylem vessels and contains terpenes
• active defence examples 


  extra cellulose, callose deposition, oxidative bursts, increase chemical production, necrosis, canker
• chemical defences

  terpenoids- antifungal and antibacterial e.g menthols

  phenols- antibiotic and antifungal properties e.g tannins

  alkaloids- inhibit enzymes and protein synthesis e.g caffeine
• primary defence

  those that prevent pathogens from entering body. it is non specific
• keratinisation


  keratinoctyes migrate to surface and dry out. the cytoplasm is replaced by keratin. results in dead layer of protective cells
• sebum


  oily substance that prevents growth of pathogen
• blood clotting

  exposes collagen, activates plateles and they interact with the collagen. releases clotting factors:

  serotonin- smooth muscles contracts, reduces blood flow

  thromboplastin- triggers enzyme cascade
• scab formation

  collagen is deposited under. stem cells divide tpo form new cells which migrate to surface and differentiate
• inflammatory response

  damaged tissues release:

  cytokines- attract neutrophils

  histamine- vasodilation, more tissue fluid enters lymph
• antigens


  chemical markers on membranes. usually proteins or glycoproteins. specific to the pathogen
• phagocytes


  specialised white blood cells that engluf microbes.

  two types: neutrophils and macrophages