Exam Qs

Question 1

Explain why the response to the subsequent infection is much bigger than the response to vaccination, as shown
in Fig. 25.1.

Answer 1

memory cells already present in response to infection
- undergone primary response
clonal expansion / proliferation (1) differentiation (1)

Question 2

Antibodies have a number of mechanisms of action. For example, agglutinins cause pathogens to be rendered inactive by clumping them together.
Outline the action of opsonins.

Answer 2

increase likelihood of phagocytosis (1)
idea that binds to pathogen and phagocyte / macrophage (1)

Question 3

The component labelled Y on the antibody is a bond.
State what type of bond is found here and give its function.

Answer 3

disulfide (1)
to hold polypeptides / light chain and heavy chain together (1)

Question 4

What is meant by the term autoimmune disease?

Answer 4

abnormal immune response
against tissues in the body

Question 5

Lupus is an autoimmune disease. Lupus occurs when nuclear proteins are exposed and the immune system makes antibodies against these proteins. As a result the proteins clump together. These clumps stick to surfaces such as the blood vessel walls and cause fatigue, joint pain and skin rashes.
Suggest why antibodies specific to nuclear proteins are not normally made.

Answer 5

nuclear proteins normally, hidden in nucleus / not exposed to tissue fluids (1)

Question 6

Outline the processes that lead to the production of antibodies against an unfamiliar bacterium.

Answer 6

three from
B cells / lymphocytes, have, antigen receptor / carry antibody, on surface, specific / complementary to, only one antigen (1)
selected / activated, B cell, proliferates / clones / divides by mitosis (1)
forms / differentiates into, plasma / effector, cells (1)
which secrete antibodies specific / complementary, to antigen (1)

Question 7

Explain how T helper cells speed up t he immune response?

Answer 7

two from
(helper T cells) stimulated by antigen- presenting cells (1)
release, cytokines / interleukin 2 (1) stimulate B-cell, proliferation / mitosis / clonal expansion (1)

Question 8

Discuss the implications of the over use of antibiotics when people do not show symptoms

Answer 8

wo from
(antibiotic is) selective pressure (1)
(bacterial) gene pool / AW, has variation (1)
(only) some bacteria have resistance / some bacteria are more resistant than others (1)
two from
when exposed (to antibiotic) most-resistant survive (1)
surviving bacteria continue to reproduce to make a resistant population (1)
idea that over many generations there is an increase in proportion of resistant bacteria (under continued antibiotic pressure) (1)
antibiotic becomes ineffective / new antibiotic needed (1)

Question 9

Vaccinations are effective in preventing the spread of a range of diseases.
Explain why vaccinations are an example of artificial immunity

Answer 9

two from
antibodies produced (by person being
vaccinated) (1)
activation of (named) lymphocytes (of person being vaccinated) (1)
(specific) memory cells remain (in person being vaccinated) (1)

Question 10

In early 2006, a newspaper claimed that the drop in MMR vaccination rates had not led to the predicted increase in measles cases.
Evaluate the validity of the newspaper’s claim. Use processed data to support your argument.

Answer 10

max two from:
idea that lowest year has been cherry- picked (1)
idea that average of several years would have been a better indicator (1)
idea that level might fluctuate (1)
plus:
use of processed data to support any of the above (1)

Question 11

The MMR injection is actually a combination of three different vaccines.
It protects children against measles, mumps and rubella pathogens.
Explain why it is not possible to protect against the different pathogens using only one vaccine

Answer 11

two from
different pathogens have different antigens (1)
antigens have specific shape (1)
shape of antibody must be complementary to (specific) antigen (1)
any of the above linked to
different antibody needed for each pathogen (1)

Question 12

Suggest two reasons for the rapid spread of fungus in the elm population

Answer 12

mobile vector / insect, moving / flying from tree to tree AW (1)
low genetic diversity / lack of resistance (1) fungal spores carried by the wind AW (1) climate favouring fungal growth / spread of vector (1)
overcrowding of trees / small distance between trees (1)

Question 13

Explain how the malarial parasite is able to bypass the body’s primary defences

Answer 13

mosquito mouthparts pierce skin / AW (1) pathogen injected (directly) into blood (

Question 14

What is the role of an opsonin during this process?

Answer 14

(opsonin) binds to antigen on pathogen and, assists binding / binds, to phagocyte

Question 15

Suggest two way in which Frankincense contributes to defending the tree from pathogens

Answer 15

• prevents pathogens from entering the wound aromatic compound is antibacterial

Question 16

There are a number of different strains of the Clostridium botulinum bacterium. Different strains produce immunologically distinct forms of the toxin.
Explain why the toxins produced by the different strains are described as being ‘immunologically distinct’ and how they will be dealt with by the immune system.

Answer 16

• toxins produced by each strain will be (slightly) different
• each (botulinum) toxin will have different, 3D shape / amino acid sequence / DNA nucleotide coding sequence
• toxin, acts as / is, antigen
• immune response determined by shape of antigen
• different compounds will have different shapes
• antigen presenting cells ingest antigen and display antigen on their surfaces
• interaction between APCs and T-helper cells causes production of interleukins
• B cells activated by T-helper cells clonal selection and clonal expansion - B cells differentiate into plasma cells - plasma cells produce, antibodies / immunoglobulins
• by protein synthesis antibodies bind to and neutralise toxins

Question 17

Explain one advantage and one disadvantage of the lack of nuclei and other membranebound organelles to mammalian erythrocytes.

Answer 17

advantages
A1 more space for / can contain more / can carry more, haemoglobin / oxygen ✔
A2 can squeeze through capillaries easily ✔
disadvantages
D1 limited life span / cannot divide / cannot reproduce / cannot undergo mitosis ✔
D2 no, protein synthesis / repair ✔
D3 no respiration, in / by, mitochondria
or
no mitochondria for respiration
or
limited respiration / no aerobic respiration / only anaerobic respiration ✔

Question 18

Viruses do not use erythrocytes as host cells, whereas the malarial pathogen Plasmodium spends part of its life cycle inside erythrocytes.

Answer 18

virus
virus is unable to / cannot, replicate / reproduce, on its own / outside a host cell or virus requires host cell, machinery / DNA / RER / ribosomes, for protein synthesis
or
virus does not contain, RER / ribosomes, for protein synthesis ✔
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___
Plasmodium
idea that Plasmodium is using the host cell to hide from the immune system
or
for Plasmodium to complete its life cycle or
for Plasmodium to use as a source of food (for, growth / reproduction) ✔

Question 19

Explain why erythrocytes do not make use of any of the oxygen they are transporting

Answer 19

they don’t have any mitochondria so can’t respire aerobic

Question 20

Explain why a mutation in the viral RNA leads to a change in the 3-D shape of the protein antigens.

Answer 20

altered base sequence (of viral RNA) means, altered, primary structure /
(sequence of) amino acids;
R-groups / disulphide bonds / hydrogen bonds / ionic bonds, interact differently;
tertiary structure is determined by, bonds / R-groups / secondary structure / primary structure / sequence of amino acids;
3-D shape is tertiary structure

Question 21

Define the term parasite

Answer 21

lives, in / on / host;
gains nutrition / feeds, from (host);
at the expense of / harms (host)

Question 22

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

Answer 22

climate change / global warming / AW, may result in spread to other parts
of the world / AW;
idea of increased movement of (infected) people;
idea that (non-malaria) countries fund anti-malaria measures via international aid;
resistance of, parasite to drugs / mosquito to insecticides;

Question 23

Antibodies are important biological molecules
Describe how the structure of antibodies allows them to perform their function

Answer 23

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