Animal And Plant Pathogens Flashcards
What are communicable diseases caused by
By infective organisms known as pathogens. Include bacteria, fungi, and protoctista.
What are vectors
Carry pathogens from one organism to another, include water and insects.
Bacteria
Only a small proportion of bacteria are pathogens, causing communicable diseases.
Prokaryotes, so they have a cell structure which is very different from the eukaryotic organisms they infect. No membrane-bound nucleus or organelles.
Two ways bacteria can be classified
-By their basic shapes-they may be rod shaped, spherical, comma shaped, spiralled, and corkscrew
-By their cell walls- the two main types of bacterial cell walls have different structures and react differently with a process called gram staining. Following stain in gram positive bacteria look purple-blue under the light microscope. Gram negative bacteria appear red. This is useful because the type of cell wall affects how bacteria react to different antibiotics (a compound that kills or inhibits growth of bacteria)
Viruses
Non-living infectious agents. At 0.02-0.3 micrometers in diameter, they are around 50 times smaller in length than the average bacterium. Basic structure is some genetic material (DNA or RNA) surrounded by protein.
How do viruses work
Viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell to make more viruses. Viruses reproduce rapidly and evolve by developing adaptations to their host, which makes them very successful pathogens.
All naturally occurring viruses are pathogenic. They cause disease in every other type of organism.
What are bacteriophages
Viruses that attack bacteria. They take over the bacterial cells and use them to replicate, destroying the bacteria at the same time. People now use bacteriophages both to identify and treat some diseases, and they are very important in scientific research. Medical scientists consider viruses to be the ultimate parasites.
Protoctista (Protista)
The protoctista (now widely known as Protista) are a group of eukaryotic organisms with a wide variety of feeding methods. They include single-celled organisms and cells grouped into colonies. A small percentage of protoctista act as pathogens, causing devastating communicable diseases in both animals and plants. The Protista which cause disease are parasitic-they use people or animals as their host organism. 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-amoebic dysentery and giardia are example of these.
Fungi
Can cause devastation in plants. Eukaryotic organisms that are often multicellular, although the yeasts which cause human diseases such as thrush are single-celled. Fungi cannot photosynthesise and they digest their food extracellularly before absorbing the nutrients. Many fungi are saprophytes which means they feed on dead and decaying matter. However some fungi are parasitic, feeding on living plants and animals. These are the pathogenic fungi which cause communicable diseases. Because fungal infections often affect the leaves of plants, they stop them photosynthesising and so can quickly kill the plant. When fungi reproduce they produce millions of tiny spores which can spread huge distances, this adaptation means they can spread rapidly and widely through crop plants. Fungal diseases of plants cause hardship and even starvation in many countries around the world.
How pathogens damage the host tissues directly
Many pathogens damage host tissue- it is this damage,combined with the way in which the body of the host responds to the damage, that causes the symptoms of disease.
-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. Proctists which cause malaria are an example of this.
-Fungi digest living cells and destroy them. This combined with the response of the body to damage caused by the fungus gives the symptoms of disease.
How pathogens produce toxins which damage host tissue
-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 cannon divide. These toxins are by-product of the normal functioning of the bacteria.
-Some fungi produce toxins which affect the host cells and cause disease.
