Chapter 12-12.1- Animal and plant pathogens Flashcards
What are communicable diseases caused by?
Infective organisms known as pathogens.
Pathogens include bacteria, viruses, fungi, and protoctista. Each has a particular characteristic that affects the way they are spread and the ways we can attempt to prevent or cure the diseases they cause.
What is the difference in how communicable diseases are spread within animals and plants?
A communicable disease can be passed from one organism to another. In animals they are most commonly spread from one individual of a species to another, but they can also be spread between species.
Communicable diseases in plants are spread directly from plant to plant.
Vectors, which carry pathogen from one organism to another are involved in the spread of a number of important plant and animal diseases.
What are two common vectors?
Water and insects.
Around how many people die as a result of communicable diseases globally?
13 million people a year.
That is 23% of all deaths- non-communicable diseases cause around 68% of all deaths, and injuries cause the rest.
Types of pathogens- What are bacteria?
There are more bacteria than any other type of organism. A small proportion of these bacteria are pathogens, causing communicable diseases.
Bacteria are prokaryotes, so they have a cell structure that is very different from the eukaryotic organisms they infect. They do not have a membrane-bound nucleus or organelles.
What are the two main ways bacteria can be classified?
By their basic shape- they may be rod shaped (bactilli), spherical (cocci), comma shaped (vibrios), spiralled (spirilla), and corkscrew (spirochaetes).
Or
By their cell walls- the two main types of bacteria cell walls have different structures and react differently with a process called Gram staining.
Following staining Gram positive bacteria look purple-blue under the light microscope, for example methicillin-resistant Staphylococcus aureus (MRSA). Gram negative bacteria appear red, for example the gut bacteria Escherichia coli (E.coli). This is useful because the type of cell wall affects how bacteria react to different antibiotics.
Types of pathogens- What are viruses?
Viruses are non-living infectious agents. At 0.02-0.3 (micrometres) in diameter, they are around 50 times smaller in lenth than the average bacterium.
The basic structure of a virus is some genetic material (DNA or RNA) surrounded by protein.
Viruses invade living cells, where the genetic material oif 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.
There are even viruses that attack bacteria, known as bacteriophages. They take over the bacterial cells and then 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 parasite.
Types of pathogens- what is are protoctista?
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 plants and animals. The protists which cause disease are parasitic- they use people or animals as their host organisms.
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 examples of these.
Types of pathogens- what are fungi?
Fungal diseases are not major problems in animals, but they can cause devastation in plants. Fungi are eukaryotic organisms that are often multicellular. although the yeast which cause human diseases such as truth are single-celled.
Fungi cannot photosynthesis and they digest their food extracellularly before absorbing he 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.
Pathogens- modes of action
How do pathogens damage the host tissues directly?
Many types of pathogens damage the tissues of their host organisms. 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. Different types of pathogens attack and damage the host tissues in different ways:
- Viruses take over the cell metabolism. The viral genetic material gets into the host cell and is inserted into the hosts DNA.
The virus’s 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 the damage caused by the fungus gives the symptoms of disease.
Pathogens- modes of action
How do pathogens produce toxins which damage host tissues?
- 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. - Some fungi produce toxins which affect the host cells and cause disease.
