Chapter 12

• How are bacteria classified?

  - by shapes - rod (bacilli), spherocal (cocci), spiralled, corkscrew, comma-shaped

  
  

  - by cell walls - 2 main types of cell walls have diff structure and react diff w gram-staining - type of cell wall affects how bacteria react to diff antibiotics
• Bacteria mode of action

  - produce toxins that poison or damage the host cells, causing disease

  
  

  - some break down cell membranes, some damage or inactivate enzymes and some interfere w genetic material so cells can't divide
• Fungi - features

  - eukaryotic organisms

  - cannot photosynthesise - digest food extracellularly

  - many are saprophytes - feed on dead and decaying matter

  - some are parasitic- feeding on living plants and animals - these are the pathogenic fungi, cause communicable diseases

  - when reproduce they produce spores that can spread large distances - spread rapidly and widely through crop plants
• Fungi mode of action

  - Digest living cells and destroy them
• Viruses - features

  - non-living

  - basic structure - genetic material surrounded by protein
• Viruses mode of action

  - viral genetic material is inserted into host's DNA, taking control of cell metabolism

  - virus uses host cell to make new viruses
• Protoctista features

  - Eukaryotic organisms

  - Single celled

  - No tissue differentiation
• Protoctista mode of action

  - Some take over cells and break them open as new generation emerge

  - simply digest and use the cell contents as they reproduce
• Bacterial plant diseases

  - Ring rot

  
  

  * destroys vascular tissue in leaves and tubers
• Fungal plant diseases

  - Black sigatoka

  
  

  * hyphae pentrate and digest leaf cells, turning leaves black
• Viral plant diseases

  - tobacco mosaic virus (TMV)

  
  

  * mosaic patterns of discoloration on leaves, flowers and fruit
• Protoctista plant disease

  - potato blight

  
  

  * hyphae penetrate cells, destroying tubers, leaves, and fruit
• Bacterial animal disease

  - tuberculosis (TB)

  
  

  * destroys lung tissue, resulting in coughing, fatigue, and chest pain

  
  

  - bacterial meningitis
• Fungal animal disease

  - athlete's foot

  * digests skin on people's feet, causing cracking and itchiness

  
  

  - ring worm
• Viral animal disease

  - HIV/ AIDS

  * infects T helper cells, inhibiting immune system

  
  

  - influenza
• Protoctista animal disease

  - malaria

  
  

  * infects erythrocytes and liver cells, causing fever & fatigue
• Direct modes of transmission in animals

  - contact

  - inoculation

  - ingestion
• Contact

  - kissing or any contact w body fluids

  - direct skin-to-skin contact

  - microorganisms from faeces transmitted onto hands
• Examples of animal disease transmitted through direct contact

  - bacterial meningitis

  - athlete's foot

  - diarrhoeal diseases
• Inoculation

  - through a break in skin e.g. in sex

  - animal bite

  - puncture wound or sharing needles
• examples of animal disease transmitted through inoculation

  - HIV/ AIDS

  - rabies

  - septicaemia
• Ingestion

  - consumption of contaminated food/ drink
• examples of animal disease transmitted through ingestion

  - amoebic dysentery
• Indirect modes of transmission in animals

  - fomites

  - inhalation

  - vectors
• Fomites

  - inanimate objects (e.g. bedding/clothes/cosmetics) that transfer pathogens
• Examples of animal disease transmitted through fomites

  - athlete's foot

  - staphylococcus
• Inhalation (droplet infection)

  - breathing in droplets (of saliva/mucus expelled from mouth) containing pathogens
• examples of animal disease transmitted through inhalation

  - influenza

  - tuberculosis
• Vectors - animals

  - anything that transmits pathogens from one host to another (e.g. water & diff animals)
• example of animal disease transmitted through vectors

  - malaria (vector = mosquitoes)
• Factors affecting transmission of communicable diseases in animals

  - overcrowded living/ working conditions

  - poor nutrition

  - compromised immune system

  - poor disposal of waste, providing breeding sites for vectors

  - climate change- intro new vectors and diseases

  - culture and infrastructure

  - socioeconomic factors - lack of trained health workers and insufficient public warning of disease outbreak
• Direct transmission of pathogens between plants

  - involves direct contact of healthy plant w any part of a diseased plant
• examples of plant disease through direct transmission

  - tobacco mosaic virus (TMV)

  - potato blight
• Indirect modes of transmission in plants

  - soil contamination

  - vectors
• Soil contamination

  - Infected plants leave pathogens or reproductive spores in the soil to infect next crop
• example of plant disease transmitted through soil contamination

  - ring rot

  - black sigatoka
• Vectors of plant viruses

  - wind, water, animals, humans can act as vectors to transmit plant pathogens
• Factors affecting transmission of communicable diseases in plants

  - planting varieties of crops that are susceptible to disease

  - over-crowding increases likelihood of contact

  - poor mineral nutrition reduces resistance of plants

  - damp, warm conditions inc survival and spread of pathogens/ spores

  - climate change - icn downfall and wind promote spread
• What is callose

  a polysaccaride formed from B-glucose monomers, joined w 1,3 glycosidic bonds (& some 1,6 linkages)
• Plant physical defences

  - callose is synthesised and deposited between cell walls and membrane in cells next to infected cells as response to pathogen attack - barriers preventing pathogens entering site of infection

  - after intial infection callose continues to be deposited in cell walls - lignin added, making barrier thicker & stronger

  - callose blocks sieve plates, sealing off infected part & preventing spread of pathogens

  - callose deposited in plasmodesmata between infected cells and neighbours - sealing off from healthy cells, prevent spread