Animal And Plant Pathogens

What is communicable disease?

Disease that can be spread from one plant or animal to another.

What are communicable diseases caused by?

Infective organisms known as pathogens.

What do pathogens include?

• Bacteria.

• Viruses.

• Fungi.

• Protoctista.

How are communicable diseases spread in animals?

From one individual of a species to another, and also between species.

How are communicable diseases spread between plants?

Directly from plant to plant.

What do vectors do?

They carry pathogens from one organism to another, are involved in the spread of a number of important plant and animal diseases. Common vectors include water and insects.

Are bacteria prokaryotes of eukaryotes?

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 ways bacteria can be classified?

• By their shapes - they may be rod, spherical, coma, spiralled or corkscrew shaped.

• By their cell walls.

How can plants be classified in terms of their cell walls?

The two main types of bacterial cells have different structures and react differently with a process called grain-staining. Following staining, gram positive bacteria look purple-blue under the light microscope. Gram negative bacteria appear res. This is useful because the type of cell wall affects how bacteria react to different antibiotics.

What are viruses?

Non-living infectious agents, they are around 50 times smaller in length than the average bacterium.

What is the basic structure of a virus?

Some genetic material (DNA or RNA) surrounded by protein.

What do viruses do?

They 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.

What are all naturally occurring viruses?

Pathogenic; they take over the bacterial cells and use them to replicate, destroying the bacteria at the same time.

What do people now use bacteriophages for?

Both to identify and treat some diseases, and they are very important in scientific research. Medical scientists consider viruses to be the ultimate parasites.

What are Protoctista (Protista)?

A group of eukaryotic organisms with a wide variety of feeding methods. They include single-celled organisms and cells grouped into colonies.

What do a small percentage of Protoctista act as?

Pathogens, causing devastating communicable diseases in both animals and plants. The protists which cause disease are parasitic - they use people or animals as their host organism.

What may pathogenic protists need?

A vector, to transfer them to their hosts or they may enter the body directly polluted water.

What is a vector?

An organism that transfers a pathogen from one host to another.

What is a parasite?

An organism that lives on or within another organism (called the host) and derives nutrients at the host’s expense.

What are fungi?

Eukaryotic organisms that are often multicellular, although the yeasts which cause human diseases are single-celled.

Can fungi undergo photosynthesis?

No, they digest their food extracellularly before absorbing the nutrients. Many fungi are saprophytes, meaning they feed on dead and decaying matter.

What are some fungi?

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, what do they stop them from?

Photosynthesising, and so can quickly kill the plant.

When fungi reproduce, what to 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.

What are the two ways in which pathogens can act?

• Damaging the host tissues directly.

• Producing toxins which damage host tissues.

What do many types of pathogen do?

Damage the tissues of their host organism. It is this damage, combined with the way in which the body of the host responds to this damage, that causes the symptoms of disease.

What do viruses take over?

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 it to infect other cells.

What do some protoctista do?

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 produce.

What do fungi do to living cells?

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.

What do 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.

What do some fungi produce?

Toxins which affect the host cells and cause disease.