Communicable diseases

Question 1

4.1.1 a)

What are the types of pathogens?

Answer 1

• Bacteria
• Viruses
• Fungi
• Protoctista

Question 2

4.1.1 a)

Describe the pathogen bacteria?

Answer 2

• more bacteria than any other type of organism
  
  • small proportion of bacteria are pathogens (causing communicable diseases)
  • cause disease by damaging cells or by releasing waste products and/or toxins that are toxic to host
  • in plants - bacteria often live in vascular tissues and cause blackening and death of these tissues
• Bacteria belong to the kingdom Prokaryotae (they are prokaryotes - have a different cell structure to eukaryotic organisms that they infect
  
  • smaller than eukaryotic cells
  • do not have a membrane-bound nucleus or organelles - so can reproduce rapidly (especially in the right conditions, e.g. host body)

Question 3

4.1.1 a)

What are the ways that bacteria can be classified?

Answer 3

• by their basic shape:
  
  • rod shaped - (bacilli)
  • speherical - (cocci)
  • comma shaped - (vibrios)
  • spiralled - (spirilla)
  • corkscrew - (spirochaetes)
• by their cell wall
  
  • two main types of cell walls - have different structures and react differently with a process called Gram staining
  • after staining Gram positive bacteria look purple-blue under the light microscope, e.g. methicillin-resistant Staphylococcus aureus (MRSA)
  • Gram negative bacteria appear red, e.g. gut bacteria, E.coli
  • useful because the type of cell wall affects how bacteria react to different antibiotics (a compound that kills/inhibits the growth of bacteria)

Question 4

4.1.1 a)

Describe the pathogen virus?

Answer 4

• Viruses cause many well-known diseases in both plants and animals, e.g. HIV
• Viruses are non-living infectious agents
• 0.02 - 0.03 µm in diameter
• around 50 x smaller in length than the average bacterium
• basic structure - some genetic material (DNA/RNA) surrounded by a protein coat
• Viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell
  
  • then causes the cell to manufacture more copies of the virus
  • the host cell eventually bursts, releasing many new viruses which will infect healthy cells

Question 5

4.1.1 a)

Why are viruses such successful pathogens?

Answer 5

• viruses reproduce rapidly and evolve by developing adaptations to their host - making them very successful
• all naturally occuring viruses are pathogenic
• cause disease in every other type of organism - even bacteria

Question 6

4.1.1 a)

What are bacteriophages?

Answer 6

• Viruses that attack bacteria
• take over the bacteria cells and use them to replicate, destroying the bacteria at the same time
• Bacteriophages now used to both identify and treat some diseases, (also important in scientific research)
• viruses considered the ultimate parasites

Question 7

4.1.1 a)

Describe the pathogen protoctista?

Answer 7

• Protoctista (or protista)
• number of diseases caused by eukaryotic protoctists
• usually cause harm by entering host cells and feeding on the contents as they grow
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