Download Activity: What is an allergy?

Volume 28, Number 4, April 2016
Activity
What is an allergy?
Martin Rowland
Mark Roberts and Sheena Cruickshank’s article on pp. 6–9 covers a topic that will be of interest to a
large number of readers, particularly since it is likely that about one-quarter of readers suffer from an
allergy.
When faced with an article like this, students often ask, ‘Is this something that could be tested in an
exam?’ This shows a common misunderstanding about what knowledge examiners can expect of
students, which can lead to students trying to learn too much and failing to practise the other skills that
will be tested in their exams.
In this exercise, we will look at which aspects of the article could form the basis of a question testing
recall with understanding (assessment objective 1, abbreviated to AO1) and which could not. You may
work individually or in groups. Questions 4–8 are exam-style questions.
All four Ofqual-accredited A-level biology specifications include the immune system. Although there
are slight differences between them, there is much in common.

AQA has the topic in its common 1st year A-level/AS content, Section 3.2.4

Edexcel specification B has the topic in its 2nd year A-level content, Topic 6.7

Eduqas has the topic as one of its three A-level options — Option A.

OCR specification A has the topic in its common 1st year A-level/AS content, Module 4.1.1.
Read the three paragraphs on pp. 6–7 of the article headed ‘Sensitisation phase’ and then answer
questions 1 and 2.
Question 1
The second paragraph describes:
(a) phagocytes that become antigen-presenting cells
(b) activation of T helper cells
(c) activation of B cells by T helper cells
Does the specification you are following include any of these topics? If so, which?
Question 2
The third paragraph describes:
(a) the release of antibodies
(b) the formation of an antigen–antibody complex
(c) immunoglobulin E (IgE)
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(d) mast cells
Does the specification you are following include any of these topics? If so, which?
Now read the paragraph on p. 7 headed ‘Allergic reaction phase’, and then answer question 3.
Question 3
This paragraph includes reference to symptoms that anyone suffering an allergy will recognise —
inflammation, itchiness and a runny, or blocked, nose. These all result from the effect of histamine
released by mast cells.
Does the specification you are following include histamine in its coverage of immunity?
Answers
1 All three concepts are clearly stated in the A-level specifications of AQA, Edexcel and OCR, so
examiners could test your recall and understanding of (a), (b) and (c). The Eduqas specification does
not explicitly include these concepts.
2 The release of antibodies and the formation of an antigen–antibody complex is clearly stated in the
A-level specifications of AQA, Edexcel and OCR, so examiners could test your recall and
understanding of (a) and (b). The Eduqas specification includes the humoral response, so recall and
understanding of (a) and (b) might be expected. None of the specifications mentions immunoglobulin
E (IgE) or mast cells, so it would not be valid for examiners to test your recall of these terms.
3 None of the specifications mentions histamine, so it would not be valid for examiners to test your
recall of this substance. The Eduqas and OCR A specifications do, however, include ‘inflammation’ as
one of several non-specific defences against pathogens.
Exam-style questions
You should by now have developed a clear understanding of the content of the section on the immune
system in your specification. Questions 4–6 that follow test AO1 skills. AO1 questions test the recall
with understanding that examiners can expect of you. Question 7 tests your ability to analyse data
(AO2) and question 8 tests your ability to evaluate information (AO3). These two questions are valid
tests of these skills but neither involves knowledge of subject matter about asthma that examiners
could expect you to know.
Question 4
Explain the importance of antigen-presenting cells in the immune response against pathogens. (4
marks)
Question 5
Compare and contrast the action of B cells and T cells in the immune response against pathogens. (6
marks)
Question 6
Explain what is meant by clonal selection. (4 marks)
Question 7
Asthma affects the ability of sufferers to breathe normally. Scientists recruited volunteers who suffered
from mild asthma to take part in an investigation.
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The scientists measured a number of variables of each volunteer before and after giving them an
inhaler containing 0.38 mg of histamine. Histamine is a substance secreted naturally by cells of the
immune system. It causes local inflammation and increased mucus secretion.
(a) The volunteers were all over 18 years of age. Explain why this was important. (1 mark)
The table shows some of the scientist’s results.
Mean values obtained (± standard error
of the mean)
Before exposure to
histamine
After exposure to
histamine
Probability of difference in
means being due to chance
(p)
Number of breaths
per minute
11 ± 1
13 ± 1
p > 0.05
Volume of air
breathed/dm3
minute−1
5.2 ± 0.3
6.0 ± 0.5
p < 0.05
Forced expiratory
volume/dm3 s−1
3.2 ± 0.1
2.0 ± 0.1
p < 0.001
Heart rate/minute−1
75 ± 4
78 ± 3
p > 0.05
Variable measured
(b) What can you conclude from the information in first two rows of data in the table? Explain your
answer. (3 marks)
(c) The forced expiratory volume is the volume of air that a person can force out of their lungs in the
first second of breathing out.
(i) Which muscles does a person contract to force air out of their lungs? (1 mark)
(ii) What was the percentage decrease in forced expiratory volume after exposure to histamine? (1
mark)
(iii) Suggest an explanation for the effect of histamine on the forced expiratory volume. (1 mark)
(d) Suggest why the scientists measured each person’s heart rate. (1 mark)
Question 8
Asthma is a condition that reduces the volume of air reaching the alveoli and, hence, the volume of
oxygen getting into the blood. In severe cases, this can be fatal.
In some people, asthma results from an immune response to substances including pollen, fur, feathers
and dust mites that are harmless to most people. Asthma has many complex causes, however,
making a definitive diagnosis difficult.

The National Institute for Health and Care Excellence (NICE) has warned that up to 30% of
the people in the UK diagnosed with asthma did not show clear evidence of the condition.

A study in The Netherlands reported that about one-half of a group of 650 children diagnosed
with asthma were unlikely to have actually suffered from it.
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Across the UK, about 5.4 million people have been diagnosed with asthma. Their care costs the
National Health Service about £1 billion per year (£1 × 109 year−1).
A new method for diagnosis is to be trialled over a 6-month period in the UK. NICE has estimated that
the cost of each test will be £13.66.
Use the information above to evaluate the scientific, social and financial aspects of this proposed trial.
Use data in your evaluation. (5 marks)
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Answers
4 A good answer will include reference to four of the following:

Antigen-presenting cells originate as macrophages/as dendritic cells that ingest
pathogens/ingest toxins by endocytosis.

They then hydrolyse the pathogens /toxins into (peptide) fragments.

They then display these (peptide) fragments on their cell surface membranes.

T cells become sensitised when their own surface receptor molecules bind to a
complementary antigen displayed on an antigen-presenting cell.

Once bound to a T cell, an antigen-presenting cell secretes interleukin/secretes cytokine that
activates the bound T cell.
5 A good answer will include reference to six of the following. Note that each statement makes a clear
comparison or contrast between the two types of cell.

Both B cells and T cells have cell surface receptors.

Both B cells and T cells remain inactive until they come into contact with an antigen that is
complementary to their own surface receptors.

Once activated, both B and T cells divide by mitosis to produce large numbers of clones —
cells with the same specificity.

Following the formation of clones, some B cells and some T cells remain inactivated as
‘memory’ cells.

There are several types of activated T cell/T helper cells and T killer cells but only one type of
activated B cell/plasma cell.

B cells respond directly to antigens on the surface of a pathogen whereas T cells respond to
antigens (displayed) on the surface of antigen-presenting cells.

B cells can ingest soluble antigens, which they then display on their cell surface membranes,
but T cells do not ingest soluble antigens.

Activated B cells become plasma cells that secrete antibodies but T cells do not secrete
antibodies.
6 A good answer will include reference to the following:

There are millions of different T cells and B cells in the body.

They are different because they have different receptor molecules on their cell surface
membranes.

A B cell or T cell is ‘selected’ when its receptor molecule binds with a complementary antigen.

Once bound in this way, a B cell or T cell divides by mitosis to form a large number of
genetically identical cells — i.e. a ‘clone’.
7 (a) Being adult, the volunteers were able to give their consent to the trials or It could be considered
unethical to administer histamine to asthma sufferers who were too young to give their consent. (1)
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(b) The number of breaths remained the same since the probability of the difference being due to
chance was greater than 0.05. (1)
The increase in the volume of air breathed each minute was significant since the probability of the
difference being due to chance was less than 0.05. (1)
So histamine caused the volume of each breath to increase. (1)
(c) (i) The internal intercostal muscles. (1)
(ii) 37.5% (1)
(iii) Histamine causes local inflammation and increased mucus secretion, both of which will narrow the
bronchioles. (1)
(Narrowing of bronchioles) decreases the volume of air in the bronchioles, which can then be expelled
in 1 second. (1)
(d) Suitable suggestions include: to monitor stress levels/to enable estimates of oxygen transport in
blood. (1)
8 A good answer would include at least five of the following.

No information about how NICE makes the estimate that 30% of asthma sufferers have been
misdiagnosed so might need validation/peer review. (1)

Netherlands might have a different health system from UK/results might not be applicable to
UK. (1)

Data from Netherlands involved only children; diagnosis among adults might be different. (1)

Current mean cost to NHS per asthma patient is of the order of £185 per person per year
(£109 ÷ 5.4 × 106 people) so proposed diagnosis represents a saving of £171 per person per
year. (1)

But costs of setting up equipment and training staff might not have been taken into account.
(1)

Potential decrease in cost of future treatments of asthma not known. (1)

Better to spend money on preventative medicine rather than treatment. (1)
This resource is part of BIOLOGICAL SCIENCES REVIEW , a magazine written for A-level students by subject experts.
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Philip Allan Publishers © 2016
www.hoddereducation.co.uk/biologicalsciencesreview