Mod. 4 Communicable diseases

Question 1

What are the types of pathogen?

Answer 1

bacteria
virus
protoctista
fungi

Question 2

How do pathogens damage a host?

Answer 2

direct damage to tissues - taking over metabolism, take over cell, digesting/destroying cells.
producing toxins to damage tissues

Question 3

How do pathogens directly damage a host tissue?

Answer 3

viruses take over metabolism. Viral genetic material is injected, copied and new viruses are made, which then burst out of the cell.
Some protoctista do similar, but do not insert their DNA.
Fungi digest living cells and destroy them.

Question 4

How do toxins produced by pathogens damage host tissues?

Answer 4

Most bacteria produce toxins. Some toxins break down membranes, some inactivate enzymes, some interfere with host genetic material so cell cannot divide. By-product of normal function.
Some fungi produce toxins which affect host cells and cause disease.

Question 5

Give examples of pathogenic diseases in plants.

Answer 5

Ring rot - bacterial disease affects potatoes, tomatoes and aubergines.
tobacco mosaic virus - virus that damages leaves, flowers and fruit, and stunts growth of tobacco plants.
Blight - caused by a fungus-like protoctist.
Black sigatoka - fungus that attacks and destroys banana plant leaves.

Question 6

Give examples of pathogenic diseases in animals.

Answer 6

TB - bacterial disease
Meningitis - bacterial infection
HIV/AIDS - virus that targets T helper cells of immune system
Influenza - viral infection of epithelial cells in gas exchange system
Malaria - caused by protoctist.
Ringworm - fungal disease causing itchy rings on the skin
Athlete’s foot - fungal disease that affects the foot.

Question 7

What is direct transmission with animals?

Answer 7

The pathogen is transferred directly from one individual to another.

• direct contact (exchange of fluids, skin on skin, contact with fluids)
• inoculation (break in skin, sharing needles, bite)
• ingestion (eating contaminated food)

Question 8

What is indirect transmission with animals?

Answer 8

The pathogen travels from one individual to another indirectly

• fomites (inanimate objects, sheets, clothing, cosmetics)
• droplet infection (droplets of spit expelled in a sneeze or talking)
• Vectors (water or an immune organism transfers communicable pathogen from one to another)
• Animal to human transmission (animals can pass diseases to humans and vice versa, as well as being vectors for diseases)

Question 9

What factors increase transmission of communicable diseases between animals?

Answer 9

• overcrowded living/working conditions
• poor nutrition
• compromised immune system
• poor waste disposal
• climate change
• cultural practice
• lack of infrastructure
• socioeconomic factors

Question 10

What is direct transmission with plants?

Answer 10

direct contact of a healthy plant with any part of a diseased plant.

Question 11

What is indirect transmission with plants?

Answer 11

Transmission through a medium other than the plant.

• soil contamination (infected plants can leave pathogens in the soil)
• vectors (wind, water, animals, humans)

Question 12

What factors increase transmission of communicable diseases in plants?

Answer 12

• planting crop susceptible to disease
• over-crowded planting increasing contact
• poor mineral nutrition reduces resistance
• damp warm conditions are favourable so pathogens spread
• climate change introduces new vectors/diseases

Question 13

What physical defenses do plants have against pathogens?

Answer 13

• external barriers (waxy cuticle layer, tree bark)
• cellulose cell wall
• callose production.

Question 14

How does callose act as a defense to pathogens?

Answer 14

callose is made of β-1,3 and β-1,6 bonds between glucose molecules to make a polysaccharide. Callose is synthesised withing minutes of initial attack and is deposited between cellulose cell wall and the cell membrane, acting as barriers to pathogens trying to enter cell. Callose continues to be deposited after initial infection, lignin is added to strengthen and thicken the barrier. Callose is also deposited in the plasmodesmata between infected cells and neighbours to seal off infection.

Question 15

How do plants recognise a pathogenic attack?

Answer 15

Receptors in the cell respond to molecules produced by a pathogen, triggering release of signal molecules that turn on genes that create cellular responses such as defensive chemicals, sending of alarm signals, and callose and lignin production.

Question 16

How do plants use chemical defenses against a pathogenic infection?

Answer 16

insect repellents (pine resin, citronella)
insecticides (pyrethins, caffeine)
antibacterial compounds inc. antibiotics (phenols, gossypol, defensins, lysosomes)
antifungal compounds (phenols, gossypol, saponins, chitinases)
anti-oomycetes (glucanases)
general toxins (chemicals broken down into cyanide)

Question 17

How do mammals keep pathogens out in non-specific methods?

Answer 17

Skin prevents pathogens from entering the body, and produces oily sebum inhibiting growth of pathogens.
Mucous membranes in many body tracts trapping microorganisms.
Lysozymes in tears, urine and stomach prevent pathogens entering.
Explosive reflexes to expel pathogens (cough, sneeze, vomiting and diarrhea.

Question 18

How does blood clotting and wound repair help protect against pathogens in mammals?

Answer 18

Cuts in skin allow pathogens to access the body, blood clotting seals a wound rapidly. Platelets come into contact with collagen in skin or wall of damaged blood vessel and secretes thromboplastin and serotonin. Thromboplastin (enzyme) triggers reactions that result in blood clotting, serotinin causes smooth muscle in blood vessel walls to contract restricting blood supply to damaged area. The clot dries to form a scab, perpenantly sealing the wound.

Question 19

How does a blood clot form?

Answer 19

damaged tissues –> platelets activated by damaged tissue –> releases thromboplastin
thromboplastin catalyses prothrombin and Ca2- reaction to form thrombin. Thrombin catalyses fibrinogen to fibrin reaction. Fibrin forms a clot.

Question 20

What is the mammalian inflammatory response to pathogenic infection?

Answer 20

Mast cells are activated in damaged tissue, releasing histomines and cytokines. Histamines make blood vessels dilate (localised heat and redness prevent pathogens reproducing). Histamines also make blood vessels more leaky, forcing blood plasma out, becoming tissue fluid, causing swelling and pain. Cytokines attract phagocytes to dispose of pathogens by phagocytosis.

Question 21

How do mammals fight infection in a non-specific way?

Answer 21

Fevers - raising body temperature above 37°C inhibits pathogen reproduction, triggered by cytokines. Specific responses work better at higher temperatures.
Phagocytosis - neutrophils and macropages build up at infection and attack pathogens.

Question 22

What are the stages of phagocytosis?

Answer 22

1 - pathogens produce chemivals that atract phagocytes
2 - phagocytes recognise the non-human proteins
3 - phagocyte engulfs pathogen in a phagosome
4 - phagosome combines with lysosome forming a phagolysosome

Question 23

What are antibodies?

Answer 23

part of the specific immune system.
Y-shaped glycoproteins called immunoglobins
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Base part is the constant region, the same on every one, with the receptor binding sites and two heavy chains bound together by glycogen.
The variable region is made of the top sections of the heavy chain and the light chain, making a specific antigen binding site, specialised to the pathogen.

Question 24

How do antibodies defend the body?

Answer 24

1. antibody acts as an opsonin (signpost) signalling to phagocytes where the antigen-antibody complex is.
2. Once part of an antigen-antibody complex, the pathogen cannot effectively invade host cells.
3. Antibodies act as agglutinins, attracting other antigens to clump together.
4. act as antitoxins, binding to toxins produced by pathogens making them harmless.

Question 25

Which cells are involved in the lymphatic response?

Answer 25

T lymphocytes - made in thymus gland

B lymphocytes - made in bone marrow

Question 26

What is the role of T helper cells in specific immune response?

Answer 26

Have CD4 receptors on cell surface membrane that bind with APC antigens.
Produce interleukins, stimulating B cell activity and other T cells.

Question 27

What is the role of T killer cells in specific immune response?

Answer 27

Produce perforin killing the pathogen through puncturing the membrane making it fully permeable.

Question 28

What is the role of T memory cells in specific immune response?

Answer 28

Part of immunological memory. If an antigen is met again, they divide rapidly, forming many clones of T killer cells.

Question 29

What is the role of T regulator cells?

Answer 29

Control the extent of immune reactions, stopping the reactions once pathogen is gone. Prevents autoimmune responses.

Question 30

What is the role of plasma cells in specific immune response?

Answer 30

Produce antibodies to specific antigens and releases them into circulation. Up to 2000 antibodies produced in few day lifespan.

Question 31

What is the role of B effector cells in specific immune response?

Answer 31

Divide to form plasma cell clones.

Question 32

What is the role of B memory cells in specific immune response?

Answer 32

Form the immunological memory, remembering a specific antigen and can launch a rapid response when pathogen is encountered again.

Question 33

What is the process of cell mediated immunity?

Answer 33

T lymphocytes respond to cells that are infected by a virus or affected by a mutation.
1 - non-specific defence system. Phagocytes perform phagocytosis, form antigen-presenting cells.
2 - T helper cell receptor fits the antigen on APC, T helper cell produces interleukins, promoting more T cells to divide rapidly by mitosis. All carry the right antigen to bind to pathogen.
3 - T cell clones: develop into T memory cells for rapid response, produce interleukins for phagocytosis, produce interleukins for B cell division, stimulate clone of T killer cells specific to antigen.

Question 34

What is the process of humoral immunity?

Answer 34

Response to antigens found outside of a cell.
1 - activated T helper cell binds to antigen presenting B cell, clonal selection.
2 - interleukins produced by T helper cells activate B cells
3 - activated B cell divideds by mitosis into plasma cells and B memory cells. clonal expansion.
4 - plasma cells produce high numbers of correct antibodies complimentary to antigens on pathogen in primary immune response.
5 - B memory cells live for years, and when they meet antigen again they rapidly divide into plasma cells and produce correct antibody in secondary immune response.

Question 35

What happens with autoimmune diseases?

Answer 35

Immune system attacks “self cells”.
Causes:
Genetic, immune system responding abnormally to mild pathogen/normal body organism.
Can be stopped with immunorepressants, but leaves the body vulnerable to other communicable diseases.

Question 36

What is natural immunity?

Answer 36

Natural Active Immunity - The immune system develops antibodies which destroy an antigen when it meets it for the first time, then stores this information in T and B memory cells.
Natural Passive Immunity - antibodies cross the placenta in fetal development, so at birth there is some immunity. Mammalian milk/cholostrum is high in antibodies.

Question 37

What is artificial immunity?

Answer 37

Immunity that we do not develop ourselves.
Artificial Passive Immunity - antibodies formed in one individual are extracted and injected into bloodstream of another for temporary immunity. e.g. tetanus and rabies shots
Artificial Active Immunity - vaccination. Immune system is encouraged to make it’s own antibodies by injecting a safe form of antigen into the blood stream.

Question 38

How does the body react to form an immunisation from a vaccine?

Answer 38

1 - pathogen is made safe, such as killed or inactivated bacteria, attenuated strains, altered toxin molecules, isolated antigens, genetically engineered antigens.
2 - small amounts of antigen injected into blood
3 - primary immune response is triggered by foreign antigens. Body produces antibodies and memory cells.
4 - If pathogen is encountered again, secondary immune response is triggered.

Question 39

epidemic

Answer 39

communicable disease spreads rapidly through a lot of people at a local or national level.

Question 40

pandemic

Answer 40

communicable disease spreads rapidly across a number of countries and continents

Question 41

What is the benefit of vaccination?

Answer 41

Helps prevent epidemics and pandemics and spread of disease to a wider population.
Herd immunity protects those who cannot be vaccinated.