1/2 MOD 7

Question 1

Prions

Answer 1

Non cellular, protein that has been altered from its normal structure and can then alter other proteins to develop more prions, creating a chain like reactions.
Causes scrapie in sheep,

Question 2

Viruses

Answer 2

Non cellular, consist of DNA or RNA enclosed in protein, live inside living cell. They are so small cannot be seen with microscope. Causes influenza, cold, foot and mouth

Question 3

Bacteria

Answer 3

Prokaryotic, very simple cells without internal membranes, cell wall e.g. boils, tuberculosis

Question 4

Protozoans

Answer 4

Microscopic single celled organisms with internal membrane bound organelles, Eukaryotic e.g. malaria

Question 5

Fungi

Answer 5

Eukaryotic. Heterotrophic, cannot produce own food, organisms. Some (yeasts) are unicellular others consist of long branching threads
cause ringworm, blight in plants, mildew, Panama disease

Question 6

Macro-organisms

Answer 6

Eukaryotic. Organisms that are visible to the naked eye, also called parasites.
e.g. fleas, ticks, tapeworms, plant parasites

Question 7

Validity

Answer 7

a measure of how well experiment tests hypothesis
e.g. control variables

Question 8

accuracy

Answer 8

how close measured value is to true value
e.g. appropriate equipment and technique

Question 9

reliability

Answer 9

consistency of measurements - repeat 3x

Question 10

Risk assessment

Answer 10

do not incubate at 37 as might grow pathogenic growth

Question 11

3 modes of transmission

Answer 11

direct contact: the transfer of the pathogen via exposure to infected skin or body secretions

Indirect: the transfer of the pathogen to a new host via a non-living object

Vector transmission/borne disease, insect bites:

Question 12

Direct
PTP
DS

Answer 12

Person to person contact: transmission occurs when an infected person touches or exchanges body fluids with someone else e.g. sexually transmitted diseases, skin to skin

Droplet spread (LESS THAN 1.5m): the spray of droplets during coughing, sneezing, can spread infectious disease, requires close proximity as droplets fall to ground e.g. influenza

Question 13

Indirect
A
C
C

Answer 13

airborne transmission: some infectious agents travel long distances and remain suspended in the air for an extended period of time e.g. common cold

Contaminated objects (fomites): some organisms live on objects for a short time. If touching an object soon after an infected person does, you are exposed to infection, transmission occurs when touching nose, eyes, mouth before washing hands e.g. E.coli

Contaminated food and drinking water (vehicular transmission): infectious diseases can be transmitted via contaminated food and water E.g. E.coli is often transmitted through improperly handled produce or undercooked meat.

Question 14

Vector transmission/borne disease (insect bites)

Answer 14

Some infectious agents are transmitted by insects especially those that suck blood. These include mosquitos, fleas, ticks. The insects become infected when they feed on infected hosts, such as birds, animals, humans e.g. malaria and dengue fever

Question 15

Louis Pasteur: identifying cause of disease
1. fermentation
2. pasteurisation
3. Germ theory
4. Vaccination

Answer 15

1. fermentation: he studied fermentation of beet juice and found that the process was due to the presence of living organisms, yeast
2. Pasteurisation: Found that other microorganisms were responsible for the souring (turning to vinegar) of alcohol and that heating the solution kills bacteria. –> today, process of pasteurisation ensures milk is free of disease causing micro-organisms
3. Germ theory: Pasteur showed that microorganisms came from pre-existing microorganisms through his swan neck bottle experiment. One flask with a long straight neck and one with a curved swan neck –> Pasteur boils broth in both flasks to begin –> leaves flask in open environment for 3 days –> microbial growth was observed in the straight necked flasks but no growth in curved swan neck flask –> spontaneous generation was dead and Pasteur published his germ theory
4. he found a way to weaken bacteria so that they are introduced to a host, causing the body to recognise real infections and be ready. He produced vaccine that prevented chickens from developing chicken cholera, and a vaccine for anthrax then for rabies.
   - Pasteur had established the principle of immunity and provided an effective way to prevent infectious disease

Question 16

Robert Koch and his experiment

Answer 16

• provided proof that microscopic pathogens caused diseased through experiments with the disease in anthrax sheep
• Bacteria are isolated –> the microorganisms are grown in pure culture –> the microorganisms are identified, the microorganisms are injected into a healthy animal –> the disease is reproduced in the second animal, microorganisms are isolated from this animal –> pathogenic microorganisms are grown in pure culture –> identical microorganisms are identified –> bacteria can be compared –> Koch was able to state a series of steps that can identify the causative organism of an infectious disease.

Question 17

Kochs postulates

Answer 17

Step 1: all infected hosts must contain the suspect organism
Step 2: A pure culture of the suspect organism must be obtained
Step 3: A healthy organism infected with the pure culture must have the same symptoms as the original host
Step 4: the suspect organism must be isolated from the second host grown in pure culture and prove to be identical to the first culture
(symptoms of the disease are carefully identified and blood is examined)

Question 18

Innate immunity

Answer 18

Provides the early line of defence against microbes. Consists of cellular and biochemical defence mechanisms that are in place even before infections and are ready to respond rapidly to infections
- physical (skin, mucous membrane)
- internal (inflammation, pahocytic cells, NK cells complement proteins)

Question 19

skin

Answer 19

Skin continuously grows by new cells being produced from below. Closely packed cells to form a protective layer covered by dead cells (tough, dry
When unbroken, skin prevents the entry of pathogens. Pores in the skin secrete substances that kill bacteria

Question 20

Mucous membrane

Answer 20

Cells lining the respiratory tract and openings of the urinary and reproductive systems that secrete a protective layer of mucus. Mucus is sticky and traps pathogens and other particles. When there are many pathogens more mucus is produced to flush them out.

Question 21

Cilia

Answer 21

Hair – like projections from cells lining the air passages. Move with a wavelike motion to push pathogens from the lungs up to the through (sneeze, cough, swallowed)

Question 22

Chemical barriers

Answer 22

Acid in the stomach; alkali in the small intestine; the enzyme lysozyme, in tears. Stomach acid destroys pathogens, including those that are carried to the throat by cilia and then swallowed. Alkali destroys acid resistant pathogens. Lysozyme destroys the cell membranes of bacteria.

Question 23

Other body secretions

Answer 23

Secretions from sweat glands and oily secretions from glands in hair follicles
Contain chemicals that destroy bacteria and fungus

Tears flush out pathogen
Lysosome in tears kill pathogens, prevent from entering blood

Question 24

Physical and chemical barriers

Answer 24

skin, mucous membrane, cilia, chemical barriers, other body secretions

Question 25

phagocytic cells (engulf and destroy) (innate)

Answer 25

– Consist of white blood cells, and include macrophages, neutrophils and dendritic cell.
– The immune system depends on phagocytes distinguishing between parts of the body and particles from the outside
– Macrophages and neutrophils, can easily change their shape so that they flow around particles and completely engulf and destroy them within their cell, where they are broken up by cell enzymes - this is called phagocytosis

Question 26

phagocytosis (innate)

Answer 26

Phagocyte surrounds and engulfs foreign material > lysosome fuses with phagosome > digestive enzymes break down foreign material into smaller pieces > small waste fragments are expelled from phagocyte by exocytosis (contents are released) > surface marker protein (antigen) then displayed on the surface and is transported to the lymph node

• some phagocytes present antigen, then they will temporarily bind to T helper cell and both will release cytokines, activating T helper cell

Question 27

Natural killer cells (innate)

Answer 27

– NK cells patrol the body constantly, release chemicals when in close proximity to target cell, attack virus-infected body cells, and cancer cells
– They recognise cell surface markers/antigens on body cells. No MCH1 marker means unhealthy and destroy them by producing chemicals called perforins which are able to bind with foreign cell antigens on the surface and form pores (holes) that cause the cell to lyse (release cell contents),
– This cell death is called apoptosis

Question 28

Inflammation response
(innate)

Answer 28

– After pathogen gets through first line of defence
– Inflammation occurs when the blood vessels around an infected areas are supplied with excess blood, making the area swollen and red
– Injured cells release Chemokines. They attract neutrophils to the damaged area  useful as neutrophils can engulf and destroy the pathogens via phagocytosis
They act on mast cells which release histamines and cytokines which allow for:
o the blood vessels dilate, increasing blood flow
o Increases the permeability of blood vessels, allowing phagocytes to leave the blood vessels and move to damaged tissue
– Cytokines act as a messenger service, alerting other immune cells, like neutrophils and macrophages, to make their way to the area of infection.
– Body tissue is injured > release of histamines/ chemicals > chemicals cause increase blood flow and capillaries to dilate > blood components enter tissues  phagocytes enter tissue and help clear debris and microbes present

Question 29

Blood proteins, including members of the complement system and other mediators of inflammation (innate)

Answer 29

The complement system conists of proteins in the blood. It can help promote inflammation, flag antigens for removal (opsinistaion). When pathogen breaks through the barriers to infection the complement system is activated

Question 30

Adaptive immune system

Answer 30

If the innate immune response fails to kill the pathogen, the next line of defence, the highly specific immune system comes into action. The adaptive immune system relies on fewer types of cells to carry out it’s tasks: B cells and T cells. Both B and T cells are lymphocytes made in the bone marrow. B cells mature in the bone marrow and T cells mature in the thymus.

Question 31

Humoral response (attacks the invader with antibodies released into the blood and lymph) (B cells and their antibodies)

Answer 31

1. Extracellular pathogens containing specific antigens are free floating in the lymphatic system
2. Highly specific B cell with antibody attach to complementary antigen using the antigen-antibody complex. Becomes activated if match is complementary  the purpose of this binding is to help flag antigens as a priority to be dealt with by other parts of immune system (antibodies can only bind to specific antigens as the antigen binding sites on antibodies have specific shapes or structure)
3. T helper cell is required for full B cell activation
4. B cell undergoes clonal proliferation into plasma B cells and memory B cells
5. Plasma B cells release highly specific antibodies which circulate through the blood and bind to the antigens on the pathogens surface.

Question 32

Cell -mediated response (attacks infected cells that display the antigens.) T cells attend to APC’s

Answer 32

1. Foreign material is engulfed by macrophages which act as antigen presenting cells (presenting the antigen on their MHC II molecules)
2. Antigen presenting macrophages move to the lymph nodes where they are inspected by helper T cells. The antigen will only be recognised by the corresponding T cell receptor. (Helper T cell activated by an antigen presenting cell)
3. Once the T cell is activated it undergoes clonal proliferation and the daughter cells differentiate to produce memory T cells, more helper T cells and suppressor T cells. They also release chemicals that stimulates the cytotoxic T cells
4. Cytotoxic cells migrate to the sight of infection and bind to infected cells presented the antigen on their MHCI molecule through T cell receptor
5. Cytotoxic T cells release other chemicals (i.e. cytokine and interferon)
6. Suppressor T cells release other chemicals to stop the production and activation of cytotoxic T cells

Question 33

antibodies responses
1. neutralisation
2. Agglutination
3. activate the complement system and opsonisation

Answer 33

Secreted antibodies work to identify free pathogens (not inside cells) that are circulating throughout the body
1. Neutralisation
The released, and highly specific antibodies circulate through the blood and bind to the specific virus preventing them from entering the body cells. (Deactivating a pathogen or toxin by blocking it’s active site)

2. Agglutination
   They can also kill bacteria by making them clump together (agglutination) so they are easily ‘eaten’ by roaming phagocytes (antibodies bind to antigens on the surface of cells to form clumps of cells)
3. They can activate the Complement system + Opsonisation
   It can help promote inflammation, flag antigens for removal (opsonisation). This ensures immune cells can get to the site of infection. Phagocytes can engulf and destroy the pathogens

Question 34

Types of T cells

Answer 34

• Helper T cells (Th cells) stimulated by antigen presenting cells. Release chemicals (cytokines) to stimulate phagocytes, B cells and Cytotoxic T cells
• Cytotoxic T cells (killer) (TC cells) recognise virus infected cells and release chemicals causing death, can kill foreign cells of transplants, can kill cancer cells
• Memory TC cells stay in blood, become activated if the antigen is encountered again, allow more effective response
• Suppressor T cells are immunosuppressors that inhibit immune cells at the end of immune response

Question 35

MHCII’s role in cell mediated immunity (in the cell)

Answer 35

When a macrophage (non specific, example of antigen presenting cell) comes across foreign particle with an antigen attached to surface = engulf and destroys (phagocytosis) In this process, the antigen is moved to the surface of the macrophage and presented on its MHC-II molecule for the T cell to identify

Question 36

What stops T cells from destroying our healthy body cells?

Answer 36

Antibodies can bind to antigens directly, however, T cell receptors can only recognize antigens dispensed by the body’s own white blood cells such as B cells and Macrophages. The antigens are bound to certain receptor molecules called Major Histocompatibility Complex class 1 (MHCI) and class 2 (MHCII). These MHC molecules are called membrane-bound surface receptors on the antigen-presenting cell. Every person has their own particular ‘self’ molecules (known as MHC1 molecules) attached to every body cell. Antigen presenting cells such as macrophages, dendritic cells and activated B cells present a fragment of the antigen, attached to the MHCII molecule.
 Organ recipiants may have their immune system recognise the new organ as an antigen, because it has a different MHCI markers. This can cause someone to have their organ ‘rejected’

Question 37

Importance of antigen presentation

Answer 37

Antigen presentation is essential for the helper T cell to be activated (step 3 in diagram), as hel[per T cells need to bind to the antigen. The T cell is then able to differentiate and become cytotoxic T cells, which can kill virus infected cells.

Question 38

The role of memory T cells in the adaptive immune system:

Answer 38

Memory T cells produced are specific to the antigen encountered. They remian in the lymph nodes. On re-exposure to the same antigen-containing pathogen, they cause rapid production of the same cytotoxic T cells. This reduces the severity of symptoms, or may stop the body from dveleoping symptons at all.

Question 39

The role of memory B cells in the adaptive immune system:

Answer 39

upon initial exposure to antigen, B cells must be activated, and then can produce antibodies, as shown by the first peak. Memory B cells are also created in case they are re-exposed. Upon secondary exposure, the memory B cells are ready to multiply quicker and to secrete more antibodies. This is shown by the steeper curve for the secondary response (quicker response) and higher quantity of B cells is shown by the higher peak.