4.1 Communicable Diseases, Disease Prevention And The Immune System

Question 1

What organisms are pathogens?

Answer 1

Bacteria, viruses, fungi, protoctista.

Question 2

What communicable diseases are caused by bacteria?

Answer 2

Ring rot (potatoes and tomatoes)
Tuberculosis
Bacterial meningitis

Question 3

What communicable diseases are caused by viruses?

Answer 3

Tobacco mosaic virus
HIV/AIDS
Influenza

Question 4

What communicable diseases are caused by fungi?

Answer 4

Black Sigatoka (bananas)
Ring worm
Athletes foot

Question 5

What communicable diseases are caused by protoctista?

Answer 5

Malaria
Potato/tomato blight

Question 6

Examples of direct transmission in animals.

Answer 6

Direct contact (kissing, direct skin contact, faeces mircroorganisms on hands)
Inoculation (break in skin, animal bite, sharing needles/puncture wound)
Ingestion (contaminated food/drink, transfer from hands to mouth)

Question 7

Examples of indirect transmission in animals.

Answer 7

Fomites (inanimate objects)
Droplet infection (saliva and mucus from talking/coughing/sneezing)
Vectors (animals transmitting disease, water)

Question 8

Factors affecting transmission of communicable diseases in animals.

Answer 8

Overcrowding
Poor nutrition
Compromised immune system
Poor waste disposal
Climate change
Culture/infrastructure
Socioeconomic factors

Question 9

Examples of direct transmission in plants

Answer 9

Direct contact of healthy plant with any part of a diseased plant

Question 10

Examples of indirect transmission in plants.

Answer 10

Soil contamination (infected plants leave spores or pathogens in soil)
Vectors (wind, water, animals, humans)

Question 11

Factors affecting transmission of communicable diseases in plants.

Answer 11

Planting varieties of crops susceptible to disease
Over-crowding
Poor mineral nutrition
Damp, warm conditions
Climate change

Question 12

What is an example of a physical defence in plants and how does it work?

Answer 12

High production levels of callose.
Minutes following an attack, it’s synthesised and deposited between cell walls + cell membrane in cells next to infected cells.
Act as barrier and prevent pathogens spreading to other cells.
Lignin added, making barrier thicker + stronger
Sieve plates blocked, sealing infected region.
Deposited into plasmodesmata.

Question 13

List examples of chemical defences in plants.

Answer 13

Insect repellents
Insecticides
Antibacterial compounds (antibiotics)
Antifungal compounds
Anti-oomycetes
General toxins

Question 14

What are the body’s barriers to entry of pathogens as part of non-specific defences?

Answer 14

Skin
Body tracts lined by mucous membranes that secrete sticky mucus (which has phagocytes) and contains lysozymes
Lysozymes in tears and urine
Acid in stomach
Expulsive reflexes (coughing/sneezing, vomiting/diarrhoea)

Question 15

Non-specific defences in animals, list 2 examples and explain.

Answer 15

Blood clotting and wound repair (blood clots to seal wound, platelets come into contact with collagen/wall of damaged vessel, they adhere and secrete thromboplastin+serotonin, blood clots and blood supply is reduced to area, clot dries and forms scab to protect, cells grow below+collagen fibres deposited)
Inflammatory response (mast cells activated in damaged tissue, release histamines and cytokines, blood vessels dilate makes it hotter + pathogens can’t reproduce, walls more leaky, tissue fluid forced out, cytokines attract phagocytes)

Question 16

How do fevers act as a non-specific defence mechanism in animals?

Answer 16

Cytokines stimulate hypothalamus and temperature goes up
Higher temperatures inhibit pathogen reproduction
Specific immune system works faster at higher temperatures

Question 17

How does phagocytosis act as a non-specific defence mechanism in animals?

Answer 17

Pathogens produce chemicals that attract phagocytes, they recognise non-human proteins on the pathogen
Phagocyte engulfs pathogen and encloses it in phagosome
Phagosome combines with lysosome to form phagolysosome
Enzymes from lysosome digest and destroy pathogen.
Macrophages digest the pathogen and combine antigens with glycoproteins called the major histocompatibility complex .
MHC complex moves antigens to macrophages’s surface membrane, becomes an antigen-presenting cell.

Question 18

How are cytokines part of the non-specific animal defence?

Answer 18

Phagocytes that have engulfed a pathogen produce them
Act as cell-signalling molecules, inform phagocytes the body is under attack, stimulate them to move to site of infection
Increase body temp, stimulate specific immune system

Question 19

How are opsonins part of the non-specific animal defence?

Answer 19

Bind to pathogens, tag them to be easily recognised by phagocytes
Receptors on cell membranes that bind to common opsonins
Phagocyte engulfs opsonins then pathogen

Question 20

Structure of antibodies

Answer 20

Y-shaped glycoproteins, immunoglobulins
2 identical long polypeptide chains, heavy chains
2 shorter identical chains, light chains
Chains held together by disulfide bridges
Disulfide bridges within the polypeptide chains, holding them in shape.
Variable region, binding site
Constant region, rest of it

Question 21

How do antibodies defend the body?

Answer 21

Antibody of antigen-antibody complex acts as an opsonin so it’s easily engulfed and digested by phagocytes
Most pathogens can’t invade host cells once part of complex
Act as agglutinins, cause pathogens carrying the complexes to clump together
Prevents spreading through body, easier for phagocytes to engulf number of pathogens at the same time
Act as anti-toxins, bind to toxins produce by pathogens, makes them harmless

Question 22

How do T helper cells contribute to the specific immune response?

Answer 22

Have CD4 receptors, bind to antigens on APCs
Produce interleukins, type of cytokine, stimulate activity of B cells, increases antibody production, stimulates production of other types of T cells, attracts and stimulates macrophages to ingest pathogens w complexes

Question 23

How do T killer cells contribute to the specific immune response?

Answer 23

Destroy the pathogen carrying the antigen
Produce perforin, kills pathogen by making holes in cell membrane so its freely permeable

Question 24

How do T memory cells contribute to the specific immune response?

Answer 24

Part of the immunological memory
If they meet an antigen a second time, divide rapidly to form huge number of clones of T killer cells

Question 25

How do T regulator cells contribute to the specific immune response?

Answer 25

Suppress the immune system, acting to control and regulate it
Once a pathogen has been eliminated, they make sure the body recognises self antigens and no autoimmune response occurs

Question 26

How do plasma cells contribute to the specific immune response?

Answer 26

Produce antibodies to particular antigen, release them into circulation
Only lives for few days but produces around 2000 antibodies per second

Question 27

How do B effector cells contribute to the specific immune response?

Answer 27

Divide to form plasma cell clones

Question 28

How do B memory cells contribute to the specific immune response?

Answer 28

Live for a long time, provide immunological memory
Programmed to remember specific antigen and enable body to have rapid response when pathogen carrying that antigen is encountered again

Question 29

What is cell mediated immunity?

Answer 29

T lymphocytes respond to cells of organism that have been changed (virus infection, antigen processing, mutation)

Question 30

Describe the process of cell mediated immunity

Answer 30

Macrophages engulf and digest pathogens, become APCs
Receptors on some of T helpers fit antigens, become activated and produce interleukins, stimulate more T cells to divide rapidly by mitosis, clones of activated T helpers, carry right antigen to bind to particular pathogen
Cloned T cells either
- develop into T memory cells
- produce interleukins that stimulate phagocytosis
-produce interleukins that stimulate B cells to divide
-develop into T killer cells and destroy infected cells

Question 31

What is humoral immunity?

Answer 31

Body responds to antigens found outside cells (bacteria, fungi, APCs)

Question 32

Describe the process of humoral immunity (primary response)

Answer 32

B cell with complementary antibody binds to pathogen, engulfs it and processes it to be APC
Activated T helper cells bind to APC, clonal selection, B cell with correct antibody selected for cloning
Interleukins produced activate the B cells
B cell divides by mitosis, clonal expansion, clones of plasma cells and B memory cells
Plasma cells produce antibodies, bind to antigens, disable them or act as opsonins/agglutinins

Question 33

Describe the process of humoral immunity (secondary response)

Answer 33

Some cloned B cells develop into B memory cells
If body is infected with same pathogen again, B memory cells divide to form plasma cell clones
Produce correct antibody and wipe out pathogen before it can cause symptoms of disease