12.1 Animal and Plant Pathogens Flashcards
What causes communicable diseases?
Pathogens
Define what a ‘pathogen’ is
A bacterium, virus or another microorganism that can cause disease
What are the 4 types of pathogens?
Bacteria, Viruses, Protoctista and Fungi
Each has particular characteristic that affects how it spreads and how it’s treated
What is a communicable disease?
A disease which can spread from one organism to another
How do communicable diseases spread in animals?
From one individual to another.
They can also spread between species.
How do communicable diseases spread in plants?
From direct contact
What is a vector?
Something that doesn’t cause a disease, but spreads the disease - usually an organism
What does a vector do?
Carry pathogens from one organism to another
What are the 2 common vectors?
Water and insects
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What 2 things can be looked at to classify a bacteria?
- Their shape
2. Their cell wall
Why can bacteria be classified by looking at their basic shape?
Bacteria have different shapes. They can be:
- Rod shaped (bacili)
- Spherical (cocci)
- Comma shaped (vibrios)
- Spiralled (spirilla)
- Corkscrew shaped (spirochaetes)
Why can bacteria be classified by looking at their cell wall?
The 2 main types of bacterial cell walls have different structures and react differently with gram-staining.
Gram-positive bacteria appear purple/blue after staining under the light microscope, e.g. MRSA
Gram-negative bacteria appear red after staining under the light microscope, e.g. (gut bacteria) E.coli
Why is it useful to know the type of bacterial cell wall if you want to eliminate the bacteria?
The type of cell wall affects how bacteria will react to antibiotics
What are antibiotics?
Compounds that stunt the growth of/kill bacteria
What is a virus?
A non-living infectious agent
What is the average size of a virus? How does this compare to the average size of a bacterium?
0.02 - 0.3 microns, 50x smaller than average bacterium
What is the basic structure of a virus?
Some genetic material (DNA/RNA) surrounded by protein
What do viruses do to their host’s cells?
Invade living cells, where the genetic material of the virus overtakes the host cell, using it to produce more viruses
What is the main characteristic of viruses?
They reproduce rapidly.
They evolve by developing adaptations to the host.
This makes them very successful pathogens.
What are all naturally occurring viruses called, in terms of what they do?
Pathogenic (cause disease)
What are bacteriophages?
Viruses that attack bacteria
How do bacteriophages destroy bacteria?
Bacteriophages invade the bacterial cells and use them to replicate, destroying the bacteria in the proces
Why are bacteriophages useful for humans?
They can be used to diagnose and treat some diseases
What are protoctista (protista)?
A group of eukaryotes with a variety of feeding methods.
A small % are pathogenic.
What form can protista take?
Protoctista, also known as protista, include single-celled organisms or cells living in colonies.
What are protists called in terms of how they cause diseases?
Parasitic - they use animals or humans as the host
Why would pathogenic protists need a vector? Give an example.
To transfer them to their host.
Malaria, sleeping sickness
How else can pathogenic protists enter the body? Give an example.
Through polluted water - amoebic dysentery
How do fungal diseases affect animals in comparison to plants?
In animals, fungal diseases don’t cause a big problem.
In plants, fungal diseases can be devastating.
What are fungi in terms of their structure?
Eukaryotes.
Often multicellular.
Can be single-celled - e.g. yeasts which cause diseases in humans e.g. thrust
If fungi can’t photosynthesize, how do they obtain energy?
Fungi digest food extracellularly before absorbing the nutrients
Many fungi are saprophytes - what does this mean?
They feed on dead and decaying matter.
Some fungi are parasitic - what does this mean?
They feed on other living organisms.
Why can fungal infections quickly kill plants?
Fungal infections often affect the leaves, stopping them from photosynthesising
How are fungi well-adapted to reproduce?
When fungi reproduce, they produce millions of spores which can spread over huge distances. This means they can quickly spread through the crop.
In a host, what do most pathogens damage?
The tissues of the organism
What makes symptoms of a disease show?
The combination of tissue damage by the pathogen and how the host’s body responds to the damage
How do viruses attack host tissue?
- Viruses take over the cell’s metabolism
- Genetic material of the virus enters the host cell and is inserted into the host cell’s DNA
- The virus then uses the host cell to replicate
- The new viruses burst out of the cell, killing the cell
- The new viruses spread to infect other cells
How do protista attack host tissue?
Some protoctista attack similarly to viruses - they take over cells and burst them open as new protoctista emerge.
However, protoctista don’t override the host cell’s genetic material.
Protoctista digest the cell’s contents and use it to reproduce
How do fungi attack host tissue?
Fungi digest and kill cells.
This, combined with the body’s response to the damage, cause symptoms of the disease.
What do bacteria produce that causes damage in the host?
Toxins - these damage/poison the host cells and cause disease
What are toxins?
By-products of normal functioning in a bacteria
How do other toxins damage the host?
Some toxins break down the cell membrane.
Some toxins damage/inactivate enzymes.
Some toxins interfere with the host cell’s genetic material, meaning the host cell can no longer divide
How else do fungi damage host cells?
Some fungi release toxins which affect the host cell and cause disease
