COMMUNICABLE DISEASES

What parts of the plant does Ring Rot damage?

Leaves, tubers and fruit

What causes a communicable disease?

A pathogen

What are the 4 main types of pathogen?

1. Bacteria
2. Viruses
3. Protoctista
4. Fungi

What does a vector do?

Carry pathogens from one organism to the other

How are communicable diseases in plants spread?

Directly plant-to-plant

What proportion of bacteria cause communicable disease?

Only a small proportion

What are the two main ways bacteria are classified?

1. By shape
2. By cell wall

What shape are bacilli?

Rod-shaped

What is chain of bacteria called?

Strepto-species type
i.e. Streptobacilli

What is a cluster of bacteria called?

Staphylo-species type
i.e. staphylococci

What shape is a vibrios?

Comma shaped

What is a corkscrew-shaped bacterium called?

Spirochaetes

What shape is a coccus?

Spherical

What are the two types of bacterial cell wall?

Gram-positive and gram-negative

What colour do gram-positive bacteria go with gram staining?

Purple-blue

What colour do gram-negative bacteria go with gram staining?

Red

What are some features of a gram-positive cell wall (excluding colour with gram staining)

Thicker but less tough, more susceptible to antibiotics which damage the cell wall, more peptidoglycan, lower lipid content, more prominent mesosome

What makes a gram-positive cell wall go purple-blue with gram staining?

The peptidoglycan in their cell wall retains crystal violet stain

What are some features of a gram-negitive cell wall (excluding colour with gram staining)?

Thinner but tougher, higher lipid content due to outer cell membrane, less susceptible to antibiotics

What is an example of a bacterium with a gram-positive cell wall?

MRSA

What is an example of a bacterium with a gram-negative cell wall?

E.coli

What is a bacterial cell wall mostly made up of?

Peptidoglycan

What is the structure of peptidoglycan?

Massive disaccharide polymers cross-linked by short chains of identical amino acid monomers

What is the basic structure of any virus?

Some genetic material (either DNA or RNA) surrounded by a protective protein coat

What is the mechanism of infection of a virus?

They attach to the cell and inject their genetic material, which takes over the biochemistry of the host cell to make more viruses by inserting itself into the host DNA, until so many are made that the host cell is lysed (bursts) and the new viruses are released

What 2 things make viruses very successful pathogens?

They reproduce rapidly and evolve by developing adaptations to their host

What proportion of naturally occurring viruses are pathogenic?

All of them

How many other types of organism do viruses infect?

Every other type of organism, including other viruses

What is a bacteriophage?

A virus which attacks a bacteria

What is a virophage? Give an example

A virus which infects other viruses, such as the Sputnik virus

Are protoctista eukaryotic or prokaryotic?

Eukaryotic, with a wide variety of feeding methods

What proportion of protoctista are pathogenic?

Only a small percentage, most are harmless

What are fungi a major problem for?

Some plants- they tend not to be a major problem for animals

Are fungi eukaryotic or prokaryotic?

Eukaryotic

Are protoctista unicellular or multicellular?

Unicellular, although they can group into colonies

Are fungi unicellular or multicellular?

Usually multicellular, with the exception of yeasts

How do fungi feed?

Many are saprophytes, but the pathogenic ones are parasites and eat living organisms. They can't photosynthesise, so digest food outside of their cells before absorbing the nutrients

What do saprophytes feed on?

Dead and decaying matter

What part of a plant do many plant fungal diseases affect?

The leaves, stopping the plant photosynthesising and killing it rapidly

How do fungi reproduce?

They produce millions of spores, which can spread huge distances and spread their disease quickly among crops

What organelles does yeast have?

Nucleus, mitochondria, cell membrane and a permanent vacuole

Apart from yeast organelles, what organelles may a more complex fungus have?

A cell wall (and vesicles) and food storage granules of starch

What are the two main pathogenic modes of action?

1. Damaging host tissue directly
2. Producing toxins which damage host tissue

What is the mechanism of infection of fungi?

They digest and destroy living cells. This, combined with the response of the body to damage caused by the fungus, cause the disease

What is the mechanism of action of protoctista which damage host tissue directly?

They take over cells and lyse them as a new generation emerge, but do not take over the genetic material of the cell like a virus; instead, they digest and use the cell contents as they reproduce

Apart from bacteria, what type of pathogen can produce cytotoxins?

Fungi

Are bacterial toxins produced deliberately to damage the host?

No, they are a by-product of the natural function of the bacterial cell

What is the mechanism of action of most pathogenic bacteria?

They produce toxins which poison/damage the host cells in some way

What are 3 ways bacterial toxins can damage cells?

1. Breaking down cell membranes
2. Damaging/deactivating enzymes
3. Interfering with the host DNA so the cell can't replicate

What organisms does tuberculosis affect?

Humans, cows, pigs, badgers and deer

What type of pathogen is tuberculosis caused by?

Bacteria

People suffering from what other disease are more likely to suffer from tuberculosis?

HIV/AIDS

How is TB cured and prevented?

Cured with antibiotics, prevented by vaccination or better living standards

How is TB spread in humans?

Droplet infection

What is the mechanism of TB?

It damages and destroys lung tissue and suppresses the immune system so that the body is less able to fight off other diseases

How is bacterial meningitis spread?

By droplet infection

How is bacterial meningitis cured and prevented?

Curable with antibiotics if administered early enough, vaccines can protect against some forms

What are the mechanism and symptoms of bacterial meningitis?

Infection of the meninges (protective membranes on brain surface) which can spread to the rest of the body and cause fatal septicaemia. Symptoms vary depending on type of bacteria, but all share a blotchy red/purple non-blanching rash

Who are the main groups affected by bacterial meningitis?

Very young babies and 15-19 year olds

What is the mechanism of the HIV virus?

It attacks T helper cells, which gradually destroys the immune system and leaves sufferers vulnerable to secondary infection

What type of virus is HIV/AIDS?

A retrovirus

How does a retrovirus work?

A virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase, that gives them the unique property of transcribing their RNA into DNA after entering a cell. The retroviral DNA can then integrate into the chromosomal DNA of the host cell, to be expressed there.

What animals does bacterial meningitis affect?

Humans

What animals does HIV/AIDS affect?

Humans and some other primates

How is HIV spread?

Passed between people via infected bodily fluids i.e. via unprotected sex, shared needles, contaminated blood and mother to baby through either pregnancy or breastfeeding. FGM also increases its spread if equipment is reused

How is HIV cured?

No vaccine or cure but antiretroviral drugs can slow its progress

What animals does influenza affect?

Mammals and birds

What is the mechanism of influenza?

Infects ciliated epithelial cells in the gas exchange system, killing them and leaving the airways vulnerable to secondary infections such as bacterial pneumonia

What are the 3 types of influenza and which is most virulent?

A,B,C, with A being most virulent

Why is a vaccine made each year for flu?

Because flu viruses undergo small, regular mutations, so their surface antigens are constantly being reshuffled

Is the a cure for flu?

No

What is zoonosis and give an example of something that does it?

Where a disease can spread from animals to humans. An example would be influenza (swine flu or bird flu)

What causes malaria?

Several species of protoctista from the genus Plasmodium, with the most common being Plasmodium Falciparum, spread by the bite of the female Anopheles mosquito

What is the mechanism of malaria?

Infects red blood cells, liver, brain. Disease recurs, making people weak and vulnerable to secondary infection

What is the cure for malaria?

No vaccine and limited cures such as quinine, but preventative measures such as vector control through mosquito nets etc. can be very effective

What are 2 reasons malaria can be difficult to treat?

1. Protoctista 'hides' inside red blood cells
2. Caused by several different species so surface antigens may be different

What causes ringworm?

Fungi, with different fungi affecting different species.

What is a cure for ringworm or Athlete's Foot?

Antifungal creams

What are the symptoms of ringworm?

Grey-white, crusty, infectious circular area of skin which aren't damaging but are unsightly and itchy

What causes Athlete's Foot?

Tinia Pedia, a form of human ringworm fungus

Where does the Athlete's Foot fungus typically grow?

The warm, moist skin between toes, which it digests

What are the symptoms of Athlete's Foot?

Cracking and scaling which is itchy and may become sore

What animals does ringworm affect?

Mammals

What plants does Ring Rot affect?

Potatoes, tomatoes and aubergines

What is the cure for Ring Rot?

There is none

What happens to a field once it has been infected by Ring Rot?

It cannot be used to grow potatoes, tomatoes or aubergines for at least 2 years

What type of pathogen causes Ring Rot?

A bacterium

What does TMV infect?

Tobacco plants and 150 other species

How is TMV prevented and cured?

Resistant crop strains can prevent it but there is no cure

What is the mechanism of TMV?

Damages leaves, flowers and fruit, stunting growth and reducing yield, and can leads to almost total crop loss

What is Potato late blight caused by?

A fungus-like protoctista called an oomycete

How is Potato late blight prevented and cured?

No cure but can be prevented via use of resistant strains, careful management and chemical treatments

What is the mechanism of Potato late blight?

Hyphae penetrate host cells and destroy leaves, tubers and fruit, leading to millions of pounds of crop damage per year

What type of pathogen causes Black Sigatoka?

A fungus

What type of plant does Black Sigatoka affect?

Bananas

What part of the plant does Black Sigatoka affect?

The leaves

What is the mechanism of Black Sigatoka?

Hyphae penetrate and digest cells, turning leaves black. Can cause 50% reduction in yield of infected plants

How is Black Sigatoka cured and prevented?

No cure but resistant strains being developed and good husbandry and fungicide treatment can control the spread of the disease

What are the two main types of transmission of communicable diseases between animals?

Direct and indirect

What are the three main types of direct transmission in animals?

1. Inoculation
2. Direct contact
3. Ingestion