12.1 - Animal and plant pathogens

Question 1

What are the types of pathogens?

Answer 1

1) Bacteria
2) Viruses
3) Protoctista
4) Fungi

Question 2

Bacteria

Answer 2

• more bacteria than any other organism
• prokaryotes : have no membrane-bound nucleus or organelles
• Bacteria can be classified in two main ways :
  1) By their shapes - rod shaped (bacilli), spherical (cocci), comma shaped (vibrios), spiralled (spirilla), and corkscrew (spirochaetes)
  2) By their cell walls - the two cell walls have different structures and react differently with a process called gram staining. Gram positive bacteria - looks blue-purple under the microscope. Example : staphylococcus aureus (MRSA). Gram negative bacteria appears red. Example : Escherichia coli (E.coli). The type of cell wall affects how bacteria reacts to different antibiotics.

Question 3

viruses

Answer 3

• non-living infectious agents
• 0.02-0.03 um in diameter (50x smaller in length than the average bacterium)
• Basic structure: Genetic material surrounded by protein
• Viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell to make more viruses.
• reproduce rapidly and evolve by developing adaptations to their host, which makes them successful pathogens
• They cause disease in every other type of organism
• Viruses that affect bacteria is know as bacteriophages. They take over bacterial cells and use them to replicate, destroying the bacteria at the same time.
• bacteriophages are used to identify and treat diseases
• viruses are considered the ultimate parasite

Question 4

Protoctista

Answer 4

• Group of eukaryotic organisms with a wide variety of feeding methods.
• Include single-celled organisms and cells grouped into colonies
• Small percentage of protoctista act as pathogens, causing communicable diseases in both plants and animals.
• They are parasitic
• Pathogenic protists may need a vector to transfer them to their hosts - malaria and sleeping sickness are examples- or they may enter the body directly through polluted water- e.g. amoebic dysentery

Question 5

Fungi

Answer 5

• Not a major problem in animals but fatal in plants
• Eukaryotic organisms that are multicellular, although the yeast which cause human disease such as thrush are single-celled.
• Do not photosynthesise
• Digest food extracellularly before absorbing nutrients
• Many fungi are saprophytes which means they feed on dead and decaying matter.
• Some fungi are parasitic
• Fungal infections in plants often affect the leaves, stopping them from photosynthesising.
• When fungi reproduce they produce millions of tiny spores which can spread huge distances, therefore, they can spread rapidly and widely

Question 6

MODES OF ACTION : damaging the host tissues directly

Answer 6

• Viruses take over the cell metabolism. The viral genetic material gets into the host cell and is inserted into the host DNA. The virus then uses the host cell to make new viruses which then burst out of the cell, destroying it and then spread to infect other cells
• Some protoctista also take over cells and break them open as the new generation emerge, but they do not take over the genetic material of the cell. They simply digest and use the cell contents as they reproduce. Protoctists which case malaria are an example
• Fungi digest living cells and destroy them. This combined with the response of the body to the damage caused by the fungus gives symptoms of disease.

Question 7

MODES OF ACTION: Producing toxins which damage host tissues

Answer 7

• Most bacteria produce toxins that poison or damage the host cells in some way, causing disease. Some bacterial toxins damage the host cells by breaking down the cell membranes, some damage or inactivate enzymes and some interfere with the host cell genetic material so the cells cannot divide. These toxins are a by-product of the normal functioning of the bacteria.