6.3/11.1

Question 1

describe the body’s primary defence mechanism

Answer 1

the skin and mucous membranes form a primary defence mechanism against pathogens that cause infectious disease

Question 2

skin

Answer 2

• outermost layer is tough and provides a physical barrier against the entry of pathogens and physical/chemical damage
• sebaceous glands are associated with hair follicles and secrete sebum, which maintains skin moisture and slightly lowering skin pH, which inhibits the growth of bacteria and fungi

Question 3

mucous membranes

Answer 3

thinner and softer type of skin found in airways and reproductive organs

• the mucus secreted is a sticky solution of glycoproteins and traps pathogens, which are either swallowed or expelled, acting as a physical barrier
• also has antiseptic properties due to the presence of the anti-bacterial enzyme lysozyme

Question 4

how are cuts in the skin sealed?

Answer 4

1. platelets aggregate at the site forming a temporary plug
2. they release clotting factors that trigger off the cascade of reactions involved in the clotting process
3. this cascade results in the production of thrombin, an enzyme, which converts the soluble protein fibrinogen into the insoluble fibrin
4. the resulting clot is initially a gel but if exposed to the air dries to form a hard scab

Question 5

Use of phagocytes in defence

Answer 5

• ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases
• they engulf of pathogens by endocytosis and digest them with lysosomes (enzymes)

Question 6

Use of antibody production in defence

Answer 6

Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity

Question 7

define an antigen

Answer 7

any chemical that stimulates an immune response

Question 8

define a specific immune response

Answer 8

• the production of one type of antibodies specific to a particular pathogen’s antigens by lymphocytes

Question 9

describe the steps of antibody production

Answer 9

1. antigens on the pathogen stimulate cell division of the small group of lymphocytes that produce the appropriate antibody
2. plasma cells (large clones of lymphocytes) are produced within a few days and secrete large quantities of the antibody

Question 10

describe the role of antibodies

Answer 10

antibodies are large proteins that have two functional regions: a hyper variable region that binds to a specific antigen and another that helps the body fight the pathogen by

• making it more recognisable to phagocytes
• preventing viruses from docking to and entering host cells

Question 11

some of the lymphocytes produced during an infection are not active plasma cells but instead become

Answer 11

memory cells

Question 12

immunity to a disease involves

Answer 12

either having antibodies against the pathogens or memory cells that allow rapid production of the antibody

Question 13

describe the function of antibiotics

Answer 13

block processes that occur in prokaryotic cells but not eukaryotic cells. For example, bacterial DNA replication, transcription, translation, ribosome function and cell wall formation.

Question 14

what is the issue with widespread antibiotic use?

Answer 14

some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains have multiple resistance

Question 15

why can viral diseases not be treated using antibiotics?

Answer 15

Being non-living, they rely on the host cell’s enzymes for ATP synthesis and other metabolic pathways. These processes cannot be targeted by drugs as the host cell would also be damaged.

Question 16

medical name for a blood clot

Answer 16

thrombus

Question 17

coronary thrombosis is

Answer 17

the formation of blood clots in the coronary arteries - this can be a fatal condition.

Question 18

give 4 things that increase the risk of coronary thrombosis

Answer 18

coronary occlusion, damage to the capillary epithelium, hardening of the arteries, rupture of an atheroma

Question 19

Effects of HIV on the immune system and modes of transmission

Answer 19

Production of antibodies by the immune system is a complex process and includes different types of lymphocyte, including helper T-cells. The human immunodeficiency virus (HIV) invades and destroys helper T-cells. The consequence is a progressive loss of the capacity to produce antibodies.

In the early stages of infection, the immune system makes antibodies against HIV. If these can be detected in a person’s body, they are said to be HIV-positive.

HIV is a retrovirus that has genes made of RNA and uses reverse transcriptase to make DNA copies of its genes once it has entered a host cell. The rate at which helper T-cells are destroyed by HIV varies considerably and can be slowed down by using anti-retroviral drugs. In most HIV-positive patients antibody production eventually becomes so ineffective that a group of opportunistic infections strike, which would be easily fought off by a healthy immune system.

A collection of several diseases or conditions existing together is called a syndrome. When the syndrome of conditions due to HIV is present, the person is said to have acquired immune deficiency syndrome (AIDS).

AIDS spreads by HIV infection. The virus only survives outside the body for a short time and infection normally only occurs if there is blood to blood contact between infected and uninfected people. There are various ways in which this can occur:
- sexual intercourse, during which abrasions to the mucous membranes of the penis and vagina can cause minor bleeding
- transfusion of infected blood, or blood products such as Factor VIII
- sharing of hypodermic needles by intravenous drug users.

Question 20

Florey and Chain experiments

Answer 20

Florey and Chain tested penicillin on infected mice
Eight mice were injected with hemolytic streptococci and four of these mice were subsequently injected with doses of penicillin
The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential

Question 21

every organism has —– ——– on the surface of their cells

Answer 21

unique molecules

Question 22

antigens on the surface of red blood cells

Answer 22

stimulate antibody production in a person with a different blood group

Question 23

describe the presence and absence of antigens on the surface of blood cells from different blood groups

Answer 23

• all three alleles involve a basic antigen sequence called antigen H
  A: this is modified by the addition of molecule N-acetylgalactosamine
  B: additional molecule is galactose
  AB: both types of antigen
  O: neither surface glycoprotein

Question 24

what happens if a recipient is given a transfusion involving the wrong type of blood?

Answer 24

an immune response occurs. antibodies are produced, agglutination (clumping) occurs, followed by hemolysis where red blood cells are destroyed and blood may coagulate in vessels

Question 25

describe an immune response

Answer 25

1. macrophage ingests pathogen and displays antigens on it
2. helper T cell specific to the antigen is activated by the macrophage
3. B cell specific to the antigen is activated by proteins from the helper T cell
4. B cell divides repeatedly to produce antibody-secreting plasma cells
5. B cell also divides to produce memory cells
6. antibodies produced by the clone of plasma cells are specific to antigens on the pathogen and help destroy it

Question 26

how does activation of helper T cells work?

Answer 26

they have an antibody-like receptor protein in their plasma membranes, which can bind to antigens displayed by macrophages

Question 27

how does the structure of plasma cells relate to their function?

Answer 27

• the cytoplasm contains an extensive network of rough endoplasmic reticulum (rER), which manufactures, modifies, and transports proteins (antibodies).
• The range of genes expressed is lower than a typical cell as the cell produces a lot of the same protein

Question 28

define clonal selection

Answer 28

the generation of large numbers of plasma cells that produce one specific antibody type

Question 29

give and explain 4 ways in which antibodies aid the destruction of pathogens

Answer 29

1. opsonisation- make the pathogen more recognisable to phagocytes so they are more readily engulfed. also, once bound, they can link the pathogen to phagocytes
2. neutralisation of viruses and bacteria: antibodies prevent viruses from docking to / entering host cells
3. neutralisation of toxins- bind to the toxins produced by pathogens, preventing them from affecting susceptible cells
4. activation of complement- antibodies activate a complement cascade which leads to the formation of a membrane attack complex that forms a pore in the membrane of the pathogen allowing water and ions to enter the cell and causing lysis
5. agglutination of pathogens, preventing cell entry and aiding ingestion by pathogens

Question 30

what is the complement system?

Answer 30

a collection of proteins which ultimately lead to the perforation of the membranes of pathogens

Question 31

what does immunity depend upon?

Answer 31

the persistence of memory cells

Question 32

describe how vaccines lead to immunity

Answer 32

they contain antigens that trigger immunity by causing a primary immune response but do not cause the disease

if the actual pathogen enters the body, it will be destroyed by the antibodies in a secondary immune response

Question 33

what was the first infectious disease of humans to have been eradicated by vaccination?

Answer 33

smallpox

Question 34

give 3 reasons why the smallpox eradication campaign was successful

Answer 34

• only humans can catch and transmit smallpox. there is no reservoir where the disease could be maintained and re-emerged
• symptoms of infection emerge quickly and are readily visible allowing teams to ‘ring vaccinate’ all of the people who might have come into contact with the afflicted person
• immunity is long-lasting

Question 35

pathogens can either be

Answer 35

species-specific or able to cross species barriers

Question 36

define a zoonosis

Answer 36

a pathogen which can cross a species barrier
these are a growing health concern

Question 37

when and how are histamines released?

Answer 37

• by mast cells (immune cells found in connective tissue) secrete histamine in response to infection
• by basophils which circulate in the blood

Question 38

state the effect of histamine on blood vessels

Answer 38

causes the dilation of the small blood vessels in the infected area causing the vessels to become leaky. This increases the flow of fluid containing immune components to the infected area and allows for some of the immune components to leave the blood vessel resulting in both specific and non-specific responses.

Question 39

Sensitization: Initial exposure to allergen and

Allergic Reaction: Secondary exposure to same allergen

Answer 39

1. when a specific B cell first encounters the allergen, it differentiates into plasma cells and makes large quantities of antibody (IgE)
2. the IgE antibodies attach to mast cells, effectively ‘priming’ them towards the allergen
3. upon re-exposure to the allergen, the IgE-primed mast cells release large amounts of histamine which causes inflammation

Question 40

symptoms of an allergic reaction

Answer 40

nose: itching, fluid build-up, sneezing, mucus secretion and inflammation
allergic rashes and dangerous swelling (anaphylaxis)

Question 41

define monoclonal antibodies

Answer 41

highly specific, purified antibodies that are produced by a clone of cells derived from a single cell. they recognise only one antigen

Question 42

what is the use of monoclonal antibodies?

Answer 42

the treatment and diagnosis of diseases; eg the test for malaria or the creation of antibodies for injection into rabies victims

Question 43

define a hybridoma cell

Answer 43

the cells formed by fusion of antibody-producing plasma B cells and myeloma (tumour) cells, which produce monoclonal antibodies

Question 44

describe how hybridoma cells are created

Answer 44

1. antigen recognised by the antibody is injected into a mouse or other mammal
2. the mouse’s immune system makes plasma B cells that are capable of producing the desired antibody
3. plasma cells are removed from the spleen of the mouse and fused with cancer cells called myeloma cells

Question 45

describe how pregnancy tests work with a diagram

Answer 45

kits use monoclonal antibodies to detect hCG, which is produced during pregnancy by the developing embryo and the placenta. the urine of pregnant women contains detectable levels of hCG

1. free monoclonal antibodies specific to hCG are conjugated to an enzyme that changes the colour of a dye
2. a second set of monoclonal antibodies specific to hCG are immobilised to the dye substrate
3. if hCG is present in urine, it will interact with both sets of monoclonal antibody (forming an antibody ‘sandwich’)
4. when both sets of antibody are bound to hCG, the enzyme is brought into physical proximity with the dye, changing its colour
5. a third set of monoclonal antibodies will bind any unattached enzyme-linked antibodies, functioning as a control