Animal and Plant Pathogens

Question 1

What are pathogens?

Answer 1

• Infectious organisms which spread communicable diseases.
• Includes bacteria, viruses, fungi and protoctista. The type of pathogen determines how it spreads.
• A vector is something which carries a pathogen from one organism to another.

Question 2

Bacteria

Answer 2

• They are prokaryotes so they have v. different ultrastructure to the organisms they infect. Most bacteria are not pathogens.

They can be identified in 2 main ways:

1) Cell walls: bacterial cell walls react differently to a process called gram staining because of their different structures - gram pos. bacteria appears purple whereas gram neg. bacteria appears red.
- This is useful as bacteria with diff. cell walls respond differently to antibiotics.
2) Basic shapes: Bacillus (rod), Streptobacillus, Coccus (sphere), Streptococcus, Staphylococci, Vibrio (comma), Spirillum (spiral), Spirachaete (corkscrew)

Question 3

Viruses

Answer 3

• Non living infectious agents, 0.2-0.3um in diameter. All viruses are pathogens.
• Basic structure is some DNA/RNA surrounded by protein.
• They invade living cells where the genetic material takes over the host to make more viruses. They reproduce rapidly and evolve by adapting to the host.
• Bacteriophages are viruses which attack bacteria and use them to replicate, destroying them at the same time, and can be used to identify and treat disease.

Question 4

Protoctista

Answer 4

• A group of eukaryotic organisms with a variety of feeding mechanisms, which can be uni- or multicellular. Only a small amount of protoctista are pathogens.
• Parasitic, so use animals as their host organism. They may need a vector to transfer them from one organism to another, or enter directly.

Question 5

Fungi

Answer 5

• Generally multicellular eukaryotic organisms which are major problem in plants, but can affect animals.
• Digest their food extracellularly and then absorb the nutrients, meaning they feed on decaying matter.
• Fungal infections kill plants by attacking leaves and stopping them from photosynthesising.
• Reproduce by releasing millions of spores which can travel long distances.

Question 6

Pathogenic modes of action: Damaging host directly

Answer 6

• Viruses take over cell metabolism as the viral DNA/RNA is inserted into host DNA, causing new viruses to be synthesised. When viruses burst out to spread to another cell, the cell dies.
• Some protoctista take over cells and kill them as a new generation emerges like viruses. They don’t take over the genetic material but they only digest cell contents as they reproduce.
• Fungi digest living cells and destroy them.

Question 7

Pathogenic modes of actions: Producing toxins

Answer 7

• Bacteria produce toxins which poison or damage the host in some way, causing disease. Such as breaking down membranes, inactivating enzymes or interfering with genetic materials. Toxins are a by-product of normal functioning.
• Fungi can also produce toxins.

Question 8

How bacteriophages work

Answer 8

1) Attach to host.
2) Insert viral DNA/RNA
3) Replication of DNA/RNA
4) Assembly of viral protein
5) Assembly of virus
6) Lysis of host