M4, C12 Communicable Diseases

Question 1

Define

a) communicable disease
b) pathogen
c) vectors

Answer 1

Communicable disease – can be passed from one organism to another

Pathogen – disease causing micro-organism

Vectors – carry pathogens from one organism to another (water/insects)

Question 2

How do viruses cause disease?

Answer 2

1) VIrus attaches to host cell
2) It inserts genetic material / viral nucleic acid
3) The viral nucleic acid replicates
4) synthesis of viral protein
5) Virus particles assemble
6) they leave the host cell

They use the cell’s metabolism to replicate

Question 3

how is bacteria classified?

Answer 3

Shape – rod, spherical, comma, spiralled, corkscrew
Cell walls – have different structures and react with gram staining differently, which affects how they react to antibiotics
Gram positive bacteria – purple under light microscope (MRSA)
Gram negative bacteria – red under light microscope (E.coli)

Question 4

what increases the risk of catching a disease in plants

Answer 4

• Planting varieties of crops susceptible to disease
• Overcrowding
• Poor mineral nutrition reduces resistance
• Damp, warm conditions increase survival of pathogens
• Climate change – increased rainfall + wind, promote the spread

Question 5

what are the two lines of defence in mammals

Answer 5

The primary non-specific defence (always present/activated rapidly)
The specific immune response (specific to each pathogen)

Question 6

how does skin keep pathogens out

Answer 6

prevents entry, has skin flora (healthy microorganisms that outcompete pathogens, produces sebum (inhibits growth)

Question 7

how does mucus membrane keep pathogens out

Answer 7

secrete sticky mucus, traps pathogens (contains phagocytes), contains lysozyme (destroys cell walls)

Question 8

how does tears and urine keep pathogens out

Answer 8

contains lysosomes

Question 9

how does stomach acid keep pathogens out

Answer 9

kills pathogens

Question 10

what expulsive reflexes does our body do

Answer 10

Coughs and sneezes from gas exchange system

Diarrhoea and vomiting expel contents of gut

Question 11

what is the process of blood clotting

Answer 11

When you cut yourself:
-Platelets come in contact with collagen in the skin
-Platelets stick to each other
-Secrete several substance
Thromboplastin – enzyme that initiates a cascade of reactions to the formation of a blood clot
Serotonin – causes smooth muscle in walls to contract (narrowing reduces blood supply to area
-Clot dries out, forming a hard, tough scab
-Epidermal cells below start to grow, sealing wound permanently
-Damages blood vessels regrow
-Collagen fibres deposited to give new tissue strength

Question 12

what is

• thromboplastin
• prothrombin
• thrombin
• fibrinogen
• fibrin

Answer 12

Thromboplastin - enzyme
Prothrombin - clotting factors made by the liver
Thrombin - enzyme that converts fibrinogen to fibrin
Fibrinogen - is a glycoprotein
Fibrin - is a fibrous, non-globular protein

Question 13

what is the body’s inflammatory response

Answer 13

= Pain, heat, redness and swelling of tissue

Mast cells (type of WBC) in damaged tissue release

–Histamine
Causes blood vessels to dilate and walls to become leaky (leak out tissue fluid) this tissue fluid causes swelling. Also raised temp (localised heat and redness) helps prevent pathogens reproducing.

–Cytokines
Attract phagocytes to the site

Question 14

How does histamine cause the symptoms of inflammation?

Answer 14

Blood vessels dilating, causes localised redness and heat, so raises temperature to prevent pathogen reproducing

Blood vessels leaky to force blood plasma out, tissue fluid causes swelling and pain

Question 15

what is the process of phagocytosis

Answer 15

1) phagocyte is attracted by chemicals produced by the pathogen
2) phagocyte recognises pathogen as non-self and binds to it
3) phagocyte engulfs the pathogen to form phagosome - lysosome moves towards phagosome and combines with it forming a phagolysosome
4) In phagolysosome, enzymes break down the pathogen
5) Digested pathogen absorbed by phagocyte - antigens combine with MHC in the cytoplasm
6) MHC is displayed on phagocyte membrane, making an antigen presenting cell (APC)

Question 16

what is cytokines

Answer 16

A chemical produced by phagocytes that have engulfed a pathogen
They act as cell-signalling molecules, informing other phagocytes that the body is under attack and it stimulates them to move to the site of infection/inflammation
They can also increase body temp

Question 17

what is opsonins

Answer 17

chemicals that bind to pathogens and ‘tag’ them so they can be more easily recognised by phagocytes.

phagocytes have receptors on their cell membranes that bind to common opsonins and the phagocyte then engulfs the pathogen.

Question 18

what are antibodies made up of

Answer 18

two identical long polypeptide chains called the heavy chains and to much shorter identical chains called light chains.
they are held together by disulphide bridges and there are also disulphide bridges between the polypeptide chains to hold them in shape

Question 19

how do antibodies bind to antigens

Answer 19

lock and key mechanism
the variable region of the antibody is the binding site and this gives the antibody a different shape to other antibodies because each antibody is specific to an antigen
the rest of the antibody is called the constant region as its always the same

when an antibody binds to an antigen it forms an antigen-antibody complex

Question 20

what are the 4 ways in which antibodies defend the body

Answer 20

1) the antibody acts as an opsonin so the pathogen is easily engulfed and digested by phagocytes
2) stop them entering host cells
3) antibodies act as agglutinins which cause pathogens to clump together which stops them spreading and so phagocytes can engulf them at the same time
4) they act as antitoxins which bind to toxins produced by the pathogens and make them harmless

Question 21

what are the two types of lymphocytes and where are they made

Answer 21

B lymphocytes - mature in the bone marrow

T lymphocytes - mature in the thymus gland

Question 22

what are the main types of T lymphocytes

Answer 22

T helper cells
T killer cells
T memory cells
T regulator cells

Question 23

what are the main types of B lymphocytes

Answer 23

plasma cells
B effector cells
B memory cells

Question 24

what are T helper cells

Answer 24

they have receptors on their cell-surface membrane which bind the surface antigens on APCs
they produce interleukins which are a type of cytokine - they stimulate activity of B cells which increases antibody production ad stmulates other types of T cells
attracts and stimulates macrophages to ingest pathogens

Question 25

what are T killer cells

Answer 25

destroy the pathogen carrying the antigen

produce a chemical called perforin which makes holes the cell surface membrane of the pathogen so it is freely permeable

Question 26

what are T memory cells

Answer 26

part of the immunological memory

if they meet a pathogen for a second time they divide rapidly to form a huge number of clones to kill the pathogen

Question 27

what are T regulator cells

Answer 27

they suppress the immune system - control and regulate it
stop the immune response once a pathogen has been eliminated
makes sure the body recognises self antigens and doesn’t set up an autoimmune response

Question 28

what are plasma cells

Answer 28

produce antibodies to a particular antigen and release them into circulation
produces 2000 antibodies per second

Question 29

what are B effector cells

Answer 29

divide to from plasma cell clones

Question 30

what are B memory cells

Answer 30

provide immunological memory
programmed to remember a specific antigen and enable the body to make a rapid response when that antigen on a pathogen is encountered again

Question 31

in cell-mediated immunity how could cells have been changed

Answer 31

viral infection
mutation
antigen processing

Question 32

what happens in the response to cell-mediated immunity

Answer 32

1) APC presents the antigen on the surface of the cell
2) T helper cells have receptors which complement the antigen
3) when the t helper cell binds to the antigen, the t helper cell becomes activated (clonal selection)
4) They produce interleukins
5) this stimulates more T cells that are specific to the antigen to divide and form clones (clonal expansion)
6) the clones then do one of four things:
- produce interleukins to stimulate phagocytosis
- produce interleukins to stimulate B cells to divide
- differentiate into T killer cells
- differentiate into T memory cells

Question 33

whats the difference between cell mediated immunity and humoral immunity

Answer 33

cell-mediated immunity - responses to cells that have been changed in some way

humoral immunity - response to antigens found outside of cells in body fluids (bacteria and fungi)

Question 34

how does the body respond to humoral immunity?

Answer 34

1) B lymphocytes covered in antibodies bind to specific antigens (clonal selection) OR B lymphocytes engulfs the pathogen and present the antigen on the surface
2) With the help from the T helper cell interleukins, the B cells are activated and divide by clonal expansion
3) the clones develop into either plasma cells producing antibodies or into memory cells

Question 35

what is the difference between the primary and secondary immune response

Answer 35

primary response - when the pathogen enters for the first time, you have a slow recovery, B and T lymphocytes are activated and you get symptoms

secondary response - when the pathogen enters for the 2nd time, fast recovery, memory cells are activated and you have no symptoms

Question 36

What is active immunity

Answer 36

Memory cells are produced
Long term protection
Protection has to develop
Requires exposure to antigens

Question 37

What is passive immunity

Answer 37

No memory cells produced
Short term protection
Immediate protection
No exposure to antigen

Question 38

Give an example of:

• natural active immunity
• natural passive
• artificial active
• artificial passive

Answer 38

Natural active - secondary response to antigen entering the body for second time

Natural passive - antibodies from mother passing into baby in breast milk

Artificial active - vaccine with dead pathogens injected into person

Artificial passive - vaccine containing antibodies injected into person

Question 39

How do vaccines work

Answer 39

A dead or inactive pathogen enters the body. It contains the antigens from the pathogen. Antibodies are produced by the white blood cells. These bind to the antigens of the vaccine. Memory cells now know the antigen so if the pathogen returns the body can produce the right white blood cells quickly to destroy the pathogen.

Question 40

What is herd immunity

Answer 40

When a high percentage of the population is protected through a vaccine against a virus or bacteria which prevents the disease from spreading.
Protects people who can’t have the vaccine like children or ill people because the disease can’t spread.

Question 41

define parasite

Answer 41

an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense