Communicable Diseases: animal and plant pathogens

Question 1

What are communicable diseases?

Answer 1

Diseases caused by infective organisms known as pathogens.

Question 2

Examples of pathogens

Answer 2

Bacteria, viruses, fungi and protoctista.

Question 3

How are communicable diseases spread?

Answer 3

From one organisms to another. In animals this is most commonly from 1 individual of a species to another, but can be between species.

Question 4

How is disease spread in plants?

Answer 4

Spread directly from plant to plant.

Question 5

What are vectors?

Answer 5

Carry pathogens from one organism to another. e.g. mosquitos in malaria, as well as water for cholera.

Question 6

Describe bacteria

Answer 6

More than any other type of organism. Prokaryotic. No membrane bound organelles or nucleus.

Question 7

How are bacteria classified?

Answer 7

Basic shape - rod shaped (bacilli) spherical (cocci) comma shaped (vibrios) spiralled (spirilla) corkscrew (spirochaetes).
Cell wall - Gram positive bacteria look purple-blue under a light microscope, e.g. MRSA. Gram negative bacteria look red, e.g. E.coli.

Question 8

How is the method of gram staining useful?

Answer 8

The cell wall type affects how the bacteria react to different antibiotics.

Question 9

Describe a virus

Answer 9

Non-living infectious agents. 0.002-0.3 micrometers in diameter. 50x smaller in length than bacterium. Basic structure is genetic material surrounded by a protein.

Question 10

How do viruses infect?

Answer 10

Invade living cells, where the genetic material of the virus takes over the cell biochemistry of the host to reproduce. Inject genetic material to infect. They evolve and develop adaptations to their host, which makes them successful.

Question 11

What are bacteriophages?

Answer 11

Viruses that attack bacteria, by taking over the bacterial cells and use them to replicate, destroy in the bacteria in the process - parasitic relationship.

Question 12

Describe protoctista

Answer 12

Eukaryotic with a wide variety of feeding methods. This includes single-celled organisms and cells in colonies. A small % are pathogens. These are parasitic. May need a vector to transfer disease to hosts, e.g. malaria and sleeping sickness, or enter directly to the body through polluted water, e.g. dysentery.

Question 13

Describe fungi

Answer 13

More significant in plants. Eukaryotic. Multicellular. Yeasts causing human disease are single-celled, e.g. thrush. Cannot photosynthesis and digest food extracellularly. Many are saprophytes - feed on dead and decaying matter. Some are parasitic. These are pathogenic.

Question 14

How do fungal infections affect plants?

Answer 14

Often affect the leaves, stopping photosynthesis, which can kill the plant quickly. Fungi produce millions of spores, which can spread over huge distances, so can spread widely. Can causes hardship and starvation in many countries.

Question 15

How are symptoms of disease caused?

Answer 15

Damage to tissues of the host organism combined with the way in which the body of the host responds to the damage.

Question 16

How do viruses damage the host tissue?

Answer 16

Viruses take over cell metabolism. The virus attaches to the host cell, and inserts the viral nucleic acid into the host DNA. The viruses uses the host cell to replicate the viral nucleic acid, which is synthesised by the host cell. The viral particles assemble, and the host cell undergoes lysis, which spreads the viral proteins to other cells.

Question 17

How do protoctista damage the host tissue?

Answer 17

Take over cells and break them open by lysis as the new generation emerge, but do not take over genetic material. Simply digest and use the cell contents as they reproduce.

Question 18

How do bacteria damage host tissue?

Answer 18

Produce toxins that poison or damage the host cells causing disease. Some toxins break down the plasma membranes, whilst some make enzymes inactive, and others interfere with the host cells genetic material so cells cannot divide. These toxins are by-products of the normal functioning of bacterial cells.