Immune system

Question 1

Non specific immune response:

Answer 1

Mast cells detect pathogens. Release cell signalling histamine. Causes vasodilation and capillary walls more permeable to WBCs and some proteins.
Blood plasma and phagocytic WBCs enter the tissue fluid.
Increased production of tissue fluid kcausing oedema.
Excess tissue fluid drained into the lymphatic system where lymphocytes are stored.
Pathogens coming into contact with lymphocytes and initiating specific immune response.

Question 2

Outline how the structure of an antibody molecule is related to its function.

Answer 2

if structure related to suitable function
variable region is antigen binding site;
(shape of) variable region specific to antigen / amino acid sequence (of ariable region) gives, complementary / matching, shape;
hinge region allows flexibility in binding;
constant region, for binding to receptors on cells / phagocytes / mast cells;
disulphide bonds hold polypeptide chains together

Question 3

Define the term parasite (3mks) f212 june15 q2ai

Answer 3

lives, in/ on, host;
gains nutrition / feeds , from (host); [ e.g. feeds on blood / get food from it / obtains nutrients from the larger organism]
at the expense of / harms (host); [causes disease]

Question 4

Explain why the human body’s primary defences do not prevent the entry of Plasmodium into the body. f212 june15 q2aii

Answer 4

mosquito / vector / Anopheles, feeds on blood;

breaks skin / skin cannot act as barrier / mosquito pierces skin / mosquito bites skin;

Question 5

Suggest why malaria is much more common in tropical areas than in other parts of the world. f212 june15 q2aiii

Answer 5

1) suitable / AW , climate / temperature , for , mosquito / vector / Anopheles; [‘warm enough for mosquitoes’]
2) more mosquitoes live there;
3) relatively poor so methods of prevention less effective; [ e.g. can’t afford , drugs / mosquito nets / habitat management / insecticides; lack of education]

Question 6

Suggest two reasons why governments in parts of the world other than tropical areas, are also becoming increasingly concerned about malaria. f212 june15 q2aiv

Answer 6

1) climate change / global warming, may result in
spread to other parts of the world;
2) increased movement of (infected) people; [ increased tourism / easier to travel; inadvertent transport of mosquitoes]
3) (non-malaria) countries fund anti-malaria measures via international aid;
4) resistance of , parasite to drugs / mosquito to insecticides;

Question 7

In patients with IDA, anaemia is caused by the destruction of erythrocytes by phagocytosis.
Suggest why erythrocytes that contain Plasmodium are more likely to be destroyed by phagocytosis than healthy erythrocytes. f212 june15 q2bii

Answer 7

(different) chemicals that attract phagocytes (released from infected erythrocytes); [in the context of chemicals released by erythrocyte or Plasmodium// cytokines / histamine / interleukin , released]

Question 8

Antibodies are important biological molecules.
Describe how the structure of antibodies allows them to perform their function.
In your answer you should clearly link structure to function. (7mks) f212 june 2015 q6a

Answer 8

1) 2 light chains and 2 heavy chains / 4 polypeptide
chains;
2) variable region allows , binding/ attachment, to antigen;
3) two variable regions allow binding of more than one (of the same) antigen;
4) variable region on different antibodies allows specificity to different antigens;
5) constant region allows , recognition by / attachment to/ binding to, (named) phagocytes;
6) hinge (region) allows flexibility; [allows arms to , move / bend]
7) disulfide , bonds / bridges, hold, polypeptides / light and heavy chains, together;

Question 9

Outline the mode of action of antibodies in defending the body against pathogens by
describing the processes of neutralisation. (2mks) f212 june 2015 q6b

Answer 9

cover / block , binding site / antigen / receptor site (on 
pathogen);
bind to toxins; 
prevent, binding / entry, 
to (host) cell

Question 10

Outline the mode of action of antibodies in defending the body against pathogens by
describing the processes of agglutination. (2mks) f212 june 2015 q6b

Answer 10

clump / bind together , (many) pathogens;
(clump) too large to , enter (host) cell / cross membranes;
increase likelihood of being consumed by (named)
phagocyte / more can be consumed by phagocyte at
once; [eaten by phagocytes more easily]

Question 11

The term immunity is often used when describing how vaccines work.
In a piece of school homework a student wrote:
“Bacteria can evolve quickly and many are now immune to antibiotics.”
Explain why the student’s use of the word ‘immune’ was incorrect. [3mks] (f212 June 14 8b)

Answer 11

1) immunity involves/ bacteria do not have, lymphocytes / white blood cells/ antibodies / memory cells / plasma cells / an immune system;
2) (correct term) is resistant;
3) bacteria are unicellular/ only multicellular organisms (can) have an immune response;

Question 12

Why are phagocytes described as a secondary defence against pathogens? f212 june13 q3aii

Answer 12

(involved) after pathogen has entered the

body; [attacking foreign bodies after they have passed through the skin]

Question 13

Why is the response involving phagocytes regarded as non-specific? f212 june13 q3aiii

Answer 13

(phagocytes) able to, digest / break down / engulf /
target / deal with, a range of / many different, pathogens; [ bacteria or virus as synonym for pathogen if the idea of a variety is clearly present; phagocytes can break down any pathogen; phagocytes do not have (antigen-)specific receptors]

Question 14

Explain how phagocytes, such as those shown in Fig. 3.1, are able to pass from the blood into the tissue fluid. f212 june13 q3aiv

Answer 14

lobed / narrow , nucleus;
(cells) can change shape; [ in context of cell or nucleus; cells, are plastic/ have flexible structure/ have flexible membrane]
can squeeze/ move/ fit, between cells/ through pores , in (walls of) capillaries; [holes/ gaps/ fenestrations]
histamine makes, capillary walls/ endothelium, leaky;

Question 15

Bacterial pathogens initially attach to receptors on the surface of phagocytes.
Describe the process by which a pathogen is destroyed after it has become attached to the surface of a phagocyte. f212 june13 q3av

Answer 15

1 (pathogen) engulfed / enveloped / surrounded
by cytoplasm (from phagocyte); [‘pseudopodia / cytoplasm / cell membrane , extend from phagocyte’]
2 endocytosis / phagocytosis;
3 (formation of) phagosome / phagocytic vacuole / phagocytic vesicle;
4 (phago) lysosomes;
5 (lysosomes / phagosome) move towards / fuse with (each other); [attracted to / joins]
6 (named) enzyme(s) / lysins / hydrogen peroxide / free radicals (in lysosomes);
7 (pathogen) digested / broken down /hydrolysed;
8 (to) amino acid / sugar / glucose / fatty acid /glycerol;
9 (break down products) absorbed (into cytoplasm)
or unwanted products removed (by exocytosis); [enter cytoplasm]
10 cytoskeleton involved in (endocytosis/ movement of vesicles);

Question 16

Name the infective agent that causes TB. [f212 june13 q3bi]

Answer 16

Mycobacterium/ M. tuberculosis/ M. bovis;

Question 17

Describe how the infective agent that causes TB is transmitted from one individual to another. [f212 june13 q3bii]

Answer 17

droplets (containing pathogen);
(released by) coughing / sneezing;
inhaled by (uninfected), individual;

Question 18

The highest incidence of TB is associated with the low income group. Suggest three reasons why the incidence of TB is higher in the low income group. [f212 june13 q3bcii]

Answer 18

overcrowded / AW (living space);
poorly ventilated (living space);
poor diet / malnourished;
poor, health/ immune system;
homelessness;
more likely to consume, meat/ milk, from infected cattle;
vaccination/ medical treatment, more difficult to access; [healthcare more expensive; poor healthcare]

Question 19

Explain why the influenza virus is usually described as a pathogen rather than a parasite. f212 jan13 q2a

Answer 19

pathogen causes disease / not all parasites cause
disease;
(influenza) virus causes a disease / influenza is a
disease;
parasite gains , nutrition / energy , from host;
or (influenza virus) does not gain , nutrients / energy ,
from host;
virus takes over (host cell) DNA/ genetic material;

Question 20

Define the term immune response. f212 jan13 q2bi

Answer 20

(response) to an antigen;

involves, lymphocytes/ production of antibodies;

Question 21

One type of cell involved in an immune response is a plasma cell, which releases antibodies. Plasma cells contain RNA. Outline the roles of RNA in plasma cells. (6mks) f212 jan13 q2bii

Answer 21

1 antibodies are proteins; [proteins make antibodies//
antibodies are polypeptides]
2 DNA unable to leave nucleus;
3 (m)RNA, copies / is a copy of, gene(s)/ part of DNA; [(m)RNA involved in transcription of DNA// ‘a section of DNA acts as a template for RNA’ if the idea of RNA copying part of DNA is clearly present]
4 (RNA) passes, out of nucleus/ through nuclear pore/
into cytoplasm;
5 to/ at, ribosome/ RER; [in context of mRNA or tRNA]
6 ribosome made of (r)RNA;
7 (RNA needed for) protein synthesis/ formation of
polypeptides;
8 amino acids brought by (t)RNA;

Question 22

Outline two ways in which antibodies reduce the threat from pathogens. (4mks) f212 jan13 q2biii

Answer 22

if no other marks have been awarded, credit one mark max for
Z antibodies bind to antigens (on pathogen);
otherwise, mark as follows:
N1 neutralisation;
N2 antibodies , cover binding sites on pathogen / bind to toxins;
N3 prevent, binding/ entry, to (host) cell; [‘prevent (host) cell becoming infected’]
A1 agglutination/ agglutinisation;
A2 clump / bind together , (many) pathogens;
A3 (clump) too large to enter host cell / increase likelihood of being consumed by (named) phagocyte; [neutrophils/ macrophages/ monocytes]
the following could be credited:
O1 opsonisation;
O2 activation of complement;
O3 increase likelihood of being consumed by (named) phagocyte; [neutrophils / macrophages / monocytes]
L1 lysins;
L2 destroy, pathogens;

Question 23

In an attempt to reduce the consequences of further outbreaks of influenza, the government encourages immunisation of key groups of people, such as the elderly and children that have another risk factor.
Suggest two other groups who should be immunised
and explain why immunisation for them would be particularly important. (4mks) f212 jan13 q2ci

Answer 23

G1 patients with , HIV+/ AIDS / transplant / chemotherapy;
E1 weak immune system / cannot produce (many)
antibodies;
G2 pregnant women;
E2 foetus / embryo , has undeveloped immune system or antibodies can cross placenta;
G3 health workers or people , living / working , close to outbreak;
E3 likely to be at (increased) risk (of disease);
G4 those with (named) chronic diseases;
E4 inability to withstand further disease / already
being in poor health;

Question 24

Other than the direct effects on health or reducing the number of deaths, suggest a reason why spending a large amount of money on immunisation is considered worthwhile. f212 jan13 q2cii

Answer 24

idea of days lost at work / effect on economy;
idea of costing more to deal with the ill people (than the cost of vaccination);
idea of response to public opinion;
idea of health service unable to cope;
idea of eliminating a disease;

Question 25

Give one reason why, despite being aware of the immunisation programme, some people choose not to be immunised. f212 jan13 q2ciii

Answer 25

being too busy/ can’t be bothered/ feel it is unnecessary;
lack of trust in government ;
media scare stories; [conflicting research]
concerned about side effects;
cost implication to individuals;
allergic to vaccine;
altruistic reason / other people more deserving;
fear of needles;
religious / cultural / ethical , reasons;

Question 26

Actions of a B lymphocyte: 7

Answer 26

b) (i) humoral response;
(ii) (B) cell / lymphocyte,
has antigen receptor / carries antibody on its surface;
(iii) specific to / matches / complementary to, only one antigen;
(iv) clonal selection;
(v) selection / activation, of, appropriate / specific,
B lymphocyte / B cell;

(vi) by, macrophages / antigen presenting cells / dendritic cells /
T helper cells / cytokines / interleukins;
(vii) clonal expansion;
(viii) (selected cell) divides by mitosis / clones;
(ix) (B) cells, differentiate / specialise;
(x) (B cells) form, plasma / effector, cells;

(xi) (which) secrete / produce, antibodies;
ACCEPT ‘forms antigen-antibody complex’
(xii) antibodies are, specific / complementary, to antigen;
(xiii) (B cells) form memory cells;
(xiv) Either (memory cells) long-lived / remain in circulation / remain in body / provide immunological memory or (provides) secondary response
or faster / stronger, response to subsequent exposure
(of same antigen / pathogen / parasite);
DO NOT CREDIT ref to disease alone
7 max

Question 27

form part of cellular response = both
mature in thymus = (only) T (lymphocytes)
secrete substances which kill infected cells =
(only) T (lymphocytes);
manufacture antibodies = (only) B (lymphocytes)
undergo clonal expansion = both / B and T
activate other lymphocytes = (only) T (lymphocytes)

Answer 27

hinge (region) 
;
flexibility / binding of more than 
                           one
 antigen 
;
B 
constant
 / Fc 
(region) 
;
attachment / binding , to 
phagocytes 
;
C 
variable / 
hypervariable / 
Fab (region) 
;
binding / attachment , to 
antigen
s 
;