AS Science in Society – answers to chapter 1 questions
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AS Science in Society
Answers to the questions
Chapter 1 The germ theory of disease
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1 and 2 Semmelweis’s factors and observations:
 the people delivering babies (medical students seemed more likely to cause the
disease than midwives),
 the other activities of the people involved (the main difference between these
two groups of carers was that medical students also dissected corpses),
 contamination on the hands of the people (medical students moved straight
from dissection to delivering babies).
 the role of hand-washing in preventing infection (he found that the more
careful and frequent the doctors’ hand-washing the less the infection of
mothers).
3
Semmelweis suggested that an infectious agent found in corpses might be
transmitted to patients through cuts.
4
Chlorinated lime is an effective disinfectant; it kills the germs carried on the
doctors’ hands.
5
Examples:
 hand washing before eating, before preparing food, and after using toilet;
 washing fruit and vegetables;
 keeping food cold;
 keeping food covered.
6
Semmelweiss was young and inexperienced. He was proposing a significant
change in accepted practice. People seldom change their minds easily unless they
have enormous respect for the person suggesting the change. Scientific evidence
alone is very slow to change ideas. Semmelweiss’s experience is in contrast with
the rapid acceptance of Pasteur’s ideas 10 or 15 years later because Pasteur’s
reputation had already been established.
7
Preventive measures are very effective in reducing the incidence of infectious
diseases such as puerperal fever. However there is almost always a need for
curative measures as well, to treat the few cases which still occur. Antibiotics, the
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only cure for puerperal fever, were only introduced in the 1950s. Until then a few
women continued to die.
8
In developing countries many women give birth at home, assisted by a traditional
birth attendant. They have very little clean water so even if they understand the
importance of hygiene it is difficult to achieve. But also many people who have
had little or no education still use traditional practices, which may actually
introduce infection. Instruments are not sterilised, local materials such as dung or
plant material may be applied to the woman. In many areas the nearest medical
services may be too far away.
Education and training for local traditional midwives is probably the most
important way of preventing these deaths. But the midwives also need more
access to sterile equipment, antibiotics and clean water as well as support from
medically qualified staff if there are complications.
Answers which suggest that all women should give birth in modern hospitals
reflect a lack of awareness of the reality of life in the rural areas of developing
countries.
9
Lack of either sanitation or rubbish disposal made the air smell bad. This led to the
theory that the bad smells given off by any decomposing organic matter or rotten
flesh could cause disease. The theory explained the well known association
between unhygienic living conditions, and rates of infection.
10 a) Chadwick believed that the smells in the air caused the disease. He therefore
predicted that reducing smells by removing sewage would reduce disease.
b)
By washing all infected sewage into the Thames, he actually spread cholera
because at that time, many people all over London used water taken directly from
the Thames. Drinking infected water is a very effective way of catching cholera.
11
If the infectious agent multiplied in an infected person it would explain how the
disease developed in the individual. But even more important, it explained how
one infected person could supply enough material to infect a large number of
other people.
12
Snow showed clearly that there was a correlation between the water supply and
the incidence of cholera. He was not able to demonstrate a causative agent
actually in the water. He was not believed because people were unwilling to
believe in germs that they could not see, smell or taste. They wanted more
evidence before overthrowing an existing theory.
13
One way was by mapping the homes of all the people who got cholera and
showing that they all got their drinking water from the same source.
Secondly, he collected data to show that the prevalence of the disease depended
on the water company that supplied the water.
14
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It was public. It worked. It was easy to understand.
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15
The two conflicting theories led to two different, testable, predictions for the
probable distribution of cholera cases in the area. In part of South London, houses
in the same street often got water from different suppliers. One of the suppliers
provided clean unpolluted water, the other provided Thames water containing
sewage. The miasma theory would predict that people living in the same street
would breathe the same air and therefore have the same chance of getting
cholera. The water-borne theory would predict that the chance of getting cholera
depended on the water supply, not the air in that street. Snow found that the
incidence of cholera was linked to the water supply, as predicted by his theory,
but not by the miasma theory.
16
A short answer is that it is easier to believe in germs once you can actually see
them. Good microscopes allowed scientists to recognise differences between
different organisms and to learn that the organism is specific to the particular
disease.
A longer answer would require an explanation of Koch’s work. Experimental work
based on his postulates (http://web.ukonline.co.uk/b.gardner/Koch.htm) finally
confirmed the germ theory of disease.
17
It is not possible to test every situation and therefore it is always possible that
some unexpected factor could cause spontaneous generation. It is always hard to
prove a negative.
Pasteur set out to show that it does not happen under any of the conditions he
tested. He then made the generalisation that spontaneous generation is not
possible. But all such scientific theories are provisional; they might be changed by
new discoveries.
18
This suggested that the infected worms contaminated the leaves in some way –
leaving an infectious agent behind.
19
It is usually essential to demonstrate the causal agent and a plausible mechanism
(in this case for infection) before a theory can be fully accepted.
20
The front line barriers to infection shown in Figure 1.11 sometimes fail. The skin
may be cut; tetanus is an infection which enters the body via a cut. The respiratory
system may be damaged by influenza or other disease allowing infection such as
pneumonia to take hold. The stomach acid is ineffective against some microbes,
particularly if they are present in large numbers. Salmonella from infected food
enters this way.
The second line of defence, the immune system, usually deals with microbes if
they do enter the body. However, the immune system is sensitive to the overall
health of the body and malnutrition, or another infection, can make it less
effective.
21
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Death from any disease may be due to a failure of either prevention or cure.
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The most important methods for prevention of cholera are the provision of clean
water and effective sewage treatment and disposal. In Low Income countries,
neither of these measures are widely available, so once one person is infected, the
disease is able to spread rapidly. This is a particular problem when people are
crowded together as they are in refugee camps.
Death from cholera is due to dehydration rather than the toxicity of the bacteria,
and it is often possible to cure the patient if they drink large quantities of clean
water containing salts and sugar. Nowadays, health workers are all taught about
the importance of this Oral Rehydration but not everyone who gets cholera is
cared for by someone with this knowledge.
Children are particularly vulnerable because their immune systems are less
developed. They may also take less hygiene precautions.
22
The cartoon in Figure 1.14 shows that people were frightened of having the
smallpox vaccine because it was derived from cows (as the name vaccination
indicates). They thought that somehow features of the cow would be transferred
to their bodies. Many people still have exaggerated fears of vaccination but the
symptoms they fear are different. See p 21 for examples.
23 a) As part of Jenner’s medical practice, he made observations and heard information
from local farmers about how cowpox protected against smallpox. He also knew
that one attack of smallpox, if survived, meant that you would never catch it
again. This led him to the hypothesis that deliberate infection with cowpox would
give protection against smallpox.
b) and c) Jenner predicted that if someone were infected with cowpox they could later
be safely exposed to smallpox. The only way to find out whether his hypothesis
was correct was to test the prediction experimentally. He did this by infecting a
small boy with cowpox, taking some pus from cowpox spots on a milkmaid and
scratching it into the boy’s skin. When the child had recovered from the mild
cowpox illness, he deliberately infected him with smallpox, taking some pus from
a smallpox spot and scratching this into the boy’s skin. The prediction was
confirmed. The boy remained healthy.
24
Not all experiments work as planned. Most people, like the assistant, would have
just put this one down to carelessness and ignored it. They were not looking for a
vaccine at the time but Pasteur knew about Jenner’s work and recognised how
important the technique would be if it could be applied to other diseases.
Somehow, he made the connection in his mind between a batch of chicken
cholera which was less serious than usual, and the cowpox. He had the ability to
link a chance observation in one set of experiments to a different problem he had
already been thinking about.
25
Although by this time, 1879, more and more evidence was accumulating in favour
of the germ theory of disease, there were still many people like Rossignol who did
not believe it. Pasteur’s anthrax experiment provided scientists with important
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confirmation of the theory. The technique was developed using predictions made
by the germ theory. It would have been hard to explain the results using any other
theory.
It also helped acceptance by the public. This demonstration was easy to
understand. The vaccinated sheep lived, the others died. Because anthrax was a
major problem for farmers, the results of the experiment were widely publicised.
26 a) This story is one of several which do not show Pasteur’s personality in a very good
light. He was a competitive and ruthless man.
Unfortunately, because he was the acknowledged expert in the field, people
trusted his verdict on Toussaint. Peer review does not always work.
b)
The loss of new ideas and the discouragement of young scientists in this way must
slow down the development of scientific knowledge.
27
Similarities: the basic principle, of controlled exposure of the body to a microbe to
stimulate the immune system, was the same in all three cases.
Differences: Jenner did not need to find a way of weakening the smallpox virus
because he used a naturally occurring disease, cowpox, which was less serious but
similar enough to provide immunity. For most diseases there is no such mild but
similar disease, and a vaccine is a microbe weakened by treatment in the
laboratory. The discovery of ways of doing this is one of Pasteur’s important
contributions to medicine.
The research work leading to the use of the vaccine was also different. Pasteur,
working eighty years later, tested his vaccines in more carefully designed
experiments, using controls. Whereas Jenner’s first trial was on a small boy,
Pasteur tested his vaccines on animals before they were used on humans.
28
Points which might be used in the argument to support Pasteur’s decision include:
he had tested the vaccine in dogs; the patients or their parents had given consent,
even begged him to do it; he discussed the decision to treat humans with his
colleagues, including doctors. Although not all those bitten do die, the chance of
doing so was 1 in 6 (16 in 100), a high risk. As he continued to treat humans, the
statistics began to confirm that the vaccine greatly reduced the risk of developing
the disease.
Points which suggest he should have spent more time developing the vaccine
include: the fact that it had only been tested on about 50 dogs and on no other
species; he did not fully understand how his vaccine worked. (Rabies is caused by
a virus and could not therefore be seen or grown outside living tissue.) Today
Pasteur would not have been allowed to use his vaccine on humans until he had
spent far more time developing it. (The same conflict between adequate testing
and immediate need for medical care still arises today.)
29
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All new scientific claims should be confirmed by being repeated in a different
laboratory by different workers. There is always the possibility that the work
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cannot be repeated because the original results depended on some unknown local
factor or even on fraud.
30 a) Cells: Koch’s work to identify and distinguish the cells of bacteria that cause
disease.
b)
Microbes: Snow’s theory about invisible infectious agents; Koch’s identification of
bacteria that cause disease; Pasteur’s study of fermentation and experiments to
show that spontaneous generation does not happen.
c) and d) Immune system and protection by infection: longstanding practice of
immunisation against smallpox in Turkey disseminated by Lady Mary Wortley
Montagu; the work of Jenner with cowpox and Pasteur with anthrax and rabies.
31 a) Correlation: between dissecting corpses and puerperal fever; between drinking
water from a particular source and infection with cholera; between infection with
cowpox and being resistant to smallpox.
b)
Controlling factors: Pasteur’s experiments with silk worms and his classic swannecked flask studies of fermentation.
c)
Plausible mechanism: Koch’s work to identify bacteria and to show that particular
germs cause particular diseases; Pasteur’s demonstration that he had isolated and
cultured the bacterium that causes chicken cholera.
d)
Theories involving invisible objects: Snow’s theory of there being an infectious
agent in contaminated water.
e)
Imagination and conjecture: Snow’s theory of the cause of cholera at a time when
the miasma theory was dominant; Pasteur’s recognition of the significance of a
failed experiment.
f)
Testing predictions: Jenner’s prediction of the results of inoculation with cowpox;
Pasteur’s vaccination experiments notably with anthrax.
g)
Influence of earlier work: the influence of Jenner’s work on Pasteur who decided
to extend the idea beyond smallpox to other diseases.
h)
Desire to be first with a discovery: notably Pasteur in all his work.
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AS Science in Society
Answers to the questions
Chapter 2 Infectious diseases now
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
It is easier to believe in germs once you can actually see them. Good microscopes
allow you to recognise differences between different organisms, and to learn that
the organism is specific to the particular disease. More powerful microscopes also
make it possible to probe the internal structure of microbes and understand how
they cause infection.
2
Bacteria start reproducing as soon as they enter the body and multiply at a steady
rate by cell division. As the number of bacteria in the body increases, the
symptoms become worse.
A virus has to enter a cell in the body and use the mechanisms of the cell to
reproduce. Whilst the viruses are growing inside cells there will be very few
symptoms. Once the cell is full of viruses it bursts. The symptoms of the illness are
usually caused by this sudden cell damage. The viruses go on to invade new cells
and the symptoms subside until the next wave of cells burst.
3
Semmelwiess observed that childbed fever was spread by doctors or medical
students going directly from one patient to another, or from the dissecting room
to the patients. The medical students did not become ill but a doctor died from
the same symptoms after cutting himself during dissection. The explanation for
these observations is that the germs from a corpse or an infected person can be
transmitted by contact but only enter the body through cuts or wounds, common
during childbirth.
Snow observed that cholera infection seemed to be spread by contaminated
water. The explanation is that the bacteria are excreted in the diarrhoea of a sick
person. If this is allowed to contaminate drinking water then the bacteria will be
swallowed and may cause infection.
4
The most straightforward way of showing the causal link would be to devise an
experiment whereby some people were exposed to the disease by the proposed
method of transmission and to then compare their rate of infection with that of a
control group. However in most cases, this would be totally unethical. This
technique could be used on animals if there is a species which is susceptible to the
same disease.
The other important method used is to isolate the infectious organism, to identify
this organism in the ill person in every case of the disease and also in the
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transmission route. The discovery of the malaria trypanosomes inside mosquitoes
as well as in malaria patients was a vital step in understanding the transmission of
malaria.
To show that Staphylococcus infections are transmitted in hospital bedding, it
would be necessary to find the same strain of bacterium in the bedding as in the
patient. This by itself might be due to common cause and it would also be
necessary to show that killing the bacteria in the sheets reduced the transmission
rate to patients.
5
Transmission by living creatures: destruction of habitats of carriers of disease;
eradication programmes with pesticides.
Infection from clothing or bedding: use of disposable alternatives in hospitals;
inspection to ensure high standards of hygiene in the handling and laundering of
fabrics.
Direct skin contact: provision of low cost barrier prevention such as condoms;
access to diagnostic guidance from local pharmacies, on-line services and primary
health care.
Coughs and sneezes: public education along the lines of ‘coughs and sneezes
spread diseases; quarantine programmes in extreme cases.
Contaminated food and water: water and sewage treatment; regulation supported
by inspection to ensure appropriate high standards in all places where food is
stored, prepared and served.
Infection through cuts: provision of access to first aid and primary health care;
public health education about the risks.
6
Mass vaccination for all children is compulsory in some European countries.
It is well known that a few people can opt out of vaccination for their children
without risk of infection as long as the majority, about 95% are vaccinated.
However, if too many people come to rely on others to take the small risk of
vaccination in this way, infection will spread.
There is an important principle of the need for consent before any medical
procedure is carried out. Compulsory vaccination ignores the families’ rights to
give or withhold consent.
This issue is discussed in a report from the Nuffield Council on Bioethics which
uses vaccination as one of the case studies to explore in ‘Public health: the ethical
issues’. See chapters 2 and 4 in the report which can be downloaded at:
www.nuffieldbioethics.org/go/ourwork/publichealth/publication_451.html.
7
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Fleming is famous because he was the first person to recognise an antibiotic and
its potential against bacteria and therefore did the most original work.
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Some would argue that Florey and Chain should be given equal credit because
they were the ones who really recognised the significance of the discovery, and
actually developed useful penicillin production. Others would say that their
contribution, though important, was less original. In 1945 all three received a
Nobel Prize for the work.
8 a) The more often bacteria are exposed to an antibiotic, the more likely they are to
become resistant. Doctors do often prescribe antibiotics when they are not
strictly necessary. Antibiotics are useless against diseases caused by viruses.
Patients expect to get antibiotics when they are ill whether they need them or
not.
b)
The problem of antibiotic resistance was not appreciated when the drugs first
became available. It was very hard to restrict the use of drugs that were so
effective.
c)
If the use of antibiotics were restricted to situations in which they are absolutely
essential, resistance would take much longer to develop. Prescribing policies of
hospitals and primary care centres could be stricter and more tightly monitored.
9
TB is airborne therefore close contact increases the rate of transmission of the
disease. Improved housing and working conditions reduce overcrowding and
transmission of TB.
Even with improved housing, it is likely that most people are exposed to the TB
bacterium at sometime. When their nutrition is good their immune system is
usually able to protect them against the infection and the bacteria will lie dormant
in the body. Better nutrition is therefore one of the most important
improvements in social conditions.
10
The differences between the UK and countries where TB is still widespread are
almost entirely due to income. Many countries of the world do not have the
resources to provide adequate housing and living conditions. They may be unable
to pay for, or organise an immunisation programme to give BCG to all children.
Many of the people may be too poor to afford an adequate diet.
11 a) Data on the number of deaths is usually more reliable because all deaths must be
recorded and a cause of death given on the death certificate. Tuberculosis is a
notifiable disease, which means that doctors have to inform the government of
any cases they diagnose. Notifications are probably fairly accurate except that not
everyone who is ill goes to the doctor. In both cases the figures will not be 100%
reliable, particularly the earlier ones, because accurate diagnosis of the cause of
illness or death is not always possible.
b)
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Less crowded living and working conditions, pasteurisation of milk and control of
spitting in public places all reduced transmission of TB. Improved nutrition meant
that even if someone was infected, they were much less likely to become ill and
infect others.
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c)
All the changes mentioned in (b) above contributed to the decline in incidence of
TB. This was before the introduction of the BCG vaccine or of any medical cure for
TB.
d)
1940 to 1950 is the period during and immediately after the Second World War
(1939 – 1945). During the war, many people had to spend time in crowded
conditions, in military camps and in air raid shelters. Because it was difficult to
import food, nutrition standards may have declined.
e)
Mass X-ray screening meant that those with TB could be diagnosed and therefore
treated and cured at an earlier stage in the illness. They would thus infect less
other people. The mass X-ray programme has ended because there are now so
few cases of TB in the UK that it would detect very few new cases of TB. The
programme is expensive and no longer cost-effective. Nowadays the same money
would contribute more to the health of population if spent in other ways.
f)
Fig 2.16 shows the drop in notifications between 1915 and 1950 as around 40 000.
This indicates just how effective preventive measures such as reduced crowding
and nutrition are.
Between 1950 when both chemotherapy (cure) and BCG (prevention) were
introduced and 1990 the drop is also around 40 000. Cure does reduce
notifications because, as mentioned in (e) above, one person’s cure is another’s
prevention. On the basis of figure 2.16 it is hard to be sure whether chemotherapy
or BCG is the more significant in preventing the spread of TB as they were both
introduced around the same time. Other information not given here shows that
overall preventive measures such as BCG and nutrition are much more effective
than curative measures.
12
TB affects people in the 15-54 age range when they are most economically
productive. People with TB have to take months off work. This means that where
TB is common, there are many people and families that are likely to be poor.
13
Political commitment is important because an effective TB control programme
requires organisation, trained personnel, money, and the support of the whole
population.
14
Patients may find it hard to continue taking the drugs when they are apparently
cured. They need time to collect the drugs, there may be side effects and they
may simply forget. However, to ensure that the disease will not recur and to
reduce the risk of drug resistance, it is vital that treatment continues. Supervision
does improve compliance with the treatment regime. Surveillance is an
infringement of the rights of the individual in their own best interests, and in the
interests of the wider community. A decision on this will depend on cultural and
political values.
The most desirable outcome would be that people were given enough scientific
understanding and support to be prepared to continue the treatment voluntarily.
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15 a) As discussed in question 14, people may stop taking the medicine too soon for a
range of reasons. This, and the use of a single drug rather than a mixture of
several anti-TB drugs are the main reasons why resistance develops.
b)
Worldwide measures which might have prevented resistance developing are
important because diseases spread readily from one region to another. The World
Health Organisation, WHO, has now drawn on experience from all over the world
to devise a strategy for TB treatment which is designed to reduce the
development of resistance. It provides advice and financial support to put the
strategy into practice. The strategy is given at the bottom of page 28.
16
Poorly supervised TB treatment might lead to widespread development of drug
resistant strains of TB. For individual patients, any treatment is still better than no
treatment but the rights of the individual may conflict with those of the society,
for whom drug resistance is the greater danger.
17
In some countries where TB is widespread, there are people outside the reach of
health care agencies. The resources do not exist to carry out tests on all the
people who might have TB. The problems are discussed in the report on this WHO
web page:
http://www.who.int/tb/publications/global_report/2008/download_centre/en/index.html
18
Overcrowding in refugee camps. Contact between patients and a larger total
number of people. The long-term treatment may be interrupted by displacement.
Displaced people often find it hard to get adequate nutrition.
19
Resistance to a disease develops when the immune system is able to respond
quickly to a microbe it recognises from previous exposure. Influenza is caused by a
virus which mutates as it reproduces in people and in animals, forming different
strains. The virus strain which infects you a few years later may have a different
protein surface from the original infection. The immune system will not recognise
it.
20 a) Influenza vaccines cannot be prepared more than a few months before they are
needed because they have to be specific to the particular strain which is in
circulation. Mutations in the influenza virus mean that a vaccine prepared more
than a year earlier would be ineffective because it would only give protection
against an earlier strain. This makes it hard to build up large stocks of vaccine.
b) and c) When supplies are limited, some form of rationing is essential. The priorities
chosen by the Government mean that those who are most likely to die as a result
of flu, the elderly or those with chronic lung disease, are protected. Health
workers get protection so that they can look after everyone else.
21
Relevant factors include: intensive farming of poultry and other birds; people
living in close contact with birds; extent of travel by people between countries and
the trade in farm products; limited research into vaccines; limited availability of
antiviral drugs in many parts of the world.
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22
A vaccine has to be specific to the particular form of the virus. So development of
a vaccine cannot start until the virus has been identified and isolated.
23
One approach is to make vaccination mandatory so that people do not have any
choice. Another approach is public information and education to maintain
awareness of the potential consequences of an outbreak of the disease. There is
an ethical dimension to the discussion as explained in the report from the Nuffield
Council on Bioethics mentioned in the answer to question 6:
“From the first perspective, most people accept vaccines in situations in which the
incidence of a vaccine-preventable disease is high, the disease is potentially
serious and the risks from the vaccine are proportionately low. The situation is
different where incidence is relatively low, as there may be both statistical and
perceptual changes in the assessments of risks and benefits. Statistically, where
there is fairly high vaccine coverage, the risks of disease for those who are
unvaccinated may decrease (owing to population immunity) while the risks of
vaccination remain. For example, in the USA, as a result of high levels of
vaccination for measles, the risk of exposure to the disease-causing virus is very
low, while the vaccine used causes fever or rash in around 5% of cases and very
occasionally causes more severe reactions. Although healthcare professionals
consider the risks of such trade-offs carefully, low incidence of a disease may also
affect people’s perceptions of it. They may view the risks of contracting a vaccinepreventable disease not to be serious, since they are less familiar with its
symptoms or severity as a result of its low prevalence (owing to a high level of
vaccination coverage), and may be more likely to refuse vaccination.”
24
TB
Influenza
Cause
Infection by a bacterium
Infection by a virus
How it spreads
When people with the
disease cough, spit, sneeze
or talk producing droplets
with bacteria in the air.
Spread in tiny droplets
caused by coughing and
sneezing. People can
become infected by
touching something
contaminated with the
virus and then touching
their mouth or nose.
Methods of prevention
Public health measures to
improve living conditions
and reduce overcrowding.
Healthier people are less
likely to get the disease.
BCG vaccination which is
Immunisation
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only partly effective.
Treatments
Combination treatment
with antibiotics.
Factors making it difficult to Rapid development of drug
control
resistance. Needs to
sustain treatment if it is to
be effective. The AIDS
epidemic. HIV makes
people more vulnerable to
TB.
25
No drug to cure the
disease. Antiviral drugs can
help to control the
symptoms.
Frequent mutations in the
influenza viruses which
means that new vaccines
have to be developed each
year.
Interaction between
animal and human forms
of the disease.
Technical feasibility: an effective regime of antibiotics is available for treating TB
whereas antiviral drugs to deal with influenza are not yet available. Vaccines for
influenza are a challenge because of the frequent mutations that change the
characteristics of the virus.
Benefits expected: the potential or actual economic benefits of eliminating or
reducing TB in the working population are high and justify very large expenditures
on programmes to detect and cure the disease.
Economic cost: research to develop treatments for diseases that are prevalent in
the poorer parts of the world can be limited by the lack of an incentive for
commercial pharmaceutical companies to invest.
Risks: the risk and consequences of an influenza pandemic are so high that some
governments are investing substantially in research into the development of types
of vaccine and antiviral drugs.
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AS Science in Society
Answers to the questions
Chapter 3 Transport issues
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1 a) Elements have atoms of only one kind so hydrogen, oxygen and carbon are all
elements.
b)
Compounds are made up of two or more element’s atoms bonded together, so
carbon dioxide and water are both compounds. NOTE: The atoms do need to be
bonded together to form a compound, otherwise you just have a mixture of
atoms.
c)
An atom is the smallest part of an element. Each element has its own kind of
atom. So there are carbon atoms, hydrogen atoms and oxygen atoms.
d)
A molecule consists of two or more atoms joined together. The atoms can be the
same as in oxygen or different as in water or hydrocarbons.
e)
A hydrocarbon is a compound made up of just hydrogen and carbon atoms
bonded together.
f)
A chemical reaction is what has happened when atoms and molecules rearrange
themselves to form new substances. Here it is illustrated by having the
hydrocarbon reacting with the oxygen to form carbon dioxide and water. The
number of each type of atoms is the same after the reaction as before, but the
atoms are arranged differently.
g)
Combustion is a reaction between chemicals and oxygen, resulting in the release
of energy. Here it is the reaction between the hydrocarbon and oxygen molecules
to make carbon dioxide and water.
2
Diagram similar to figure 3.4 to show one molecule of propane reacting with five
oxygen molecules to make three carbon dioxide molecules and four water
molecules.
3 a) The energy industries are those which supply electricity and fuels.
b)
Up to 2005 there was no sign of any start of a significant decline in emissions. All
sectors will have to contribute to change if the targets are to be met.
4 a) Road freight: from 15 to 22 million tonnes of CO2 equivalent - an increase of about
47% in emissions.
b)
Air transport: from 20 to 37 million tonnes of CO2 equivalent - an increase of
about 85% in emissions.
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5
Biggest contribution is from air transport which has risen most in the period but
has now started to decline. Next biggest is road freight which has increased
steadily over the period. Public transport’s emissions have slowly declined during
these years. The contribution from water transport has fluctuated but not
changed greatly. (Increases in fuel costs in 2008 could have a significant impact on
these figures.)
6
The energy comes from the Sun.
7 a) Plants take in carbon dioxide and turn it into sugars and other chemicals by
photosynthesis as they grow. In theory, this balances the carbon dioxide given out
when chemicals from plants burn.
b)
Energy is needed to cultivate and harvest plants. More energy is needed to
process plant material and turn it into fuels. Supplying all this energy involves the
use of fuels that give out carbon dioxide.
c)
There is more intense sunlight in the tropics. Plants such as sugar cane need less
fertiliser and some of the energy for processing the plant material into fuel can
come from burning the dried crop waste.
8
Advantages: renewable unlike fossil fuels; reduced emissions of carbon dioxide;
can help to reduce reliance on imported fuel.
Disadvantages: grown on land that could be used to grow food; may be grown on
land made available by destroying tropical forests.
9
The key point here is that with a fuel such as gas, the energy given out when it
burns does not disappear but is still around – transferred to other things. Some
useful, some not so useful. Energy transferred to the environment will heat it up,
although only by a tiny amount if taken globally, and some will be radiated out
into space. None is lost, it is just distributed more widely. This is the principle of
conservation of energy.
10 a) Start with 6500 GJ. First arrow branches off taking 2000 GJ to produce the fuel
rods. Second arrow branches off taking 1000 GJ left in the spent fuel rods. Third
arrow branches off showing 2400 GJ thermal energy lost to the surroundings (e.g.
from cooling towers or cooling water) leaving an arrow at the end showing the
supply of 1100 GJ energy as electricity.
b)
Efficiency = (1100 GJ  6500 GJ)  100 % = 17%
11
Suck, squeeze, bang, blow. Note that there is not really such a process as ‘suck’ in
terms of a vacuum producing suction. What happens here is that the piston, in
moving down, creates a partial vacuum (low pressure) inside the cylinder. This
causes the atmosphere (high pressure) to push fuel into the cylinder.
12 1 kg is 1000 g. 1 mg is 1/1000 g. So each 1 kg is made up of 1 000 000 mg,
hence 1 ppm.
1 mg is just a few grains of salt. You would be unlikely to be able to taste it.
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13 a) Carbon monoxide and volatile organic compounds.
b)
Sulfur dioxide.
c)
Oxides of nitrogen.
14
Nitrogen dioxide is produced as there is plenty of nitrogen, approximately 78% in
fact, in the air. At low temperatures nitrogen is inert, but at the high temperature
in the cylinder of an engine it can react with oxygen.
15
If the air/fuel ratio is too low then incomplete combustion will take place leading
to the release of carbon monoxide and volatile organic compounds. Carbon
monoxide puts a strain on the heart in low doses and can be fatal in high doses.
Unburnt fuel contributes to photochemical smog. Having too high an air/fuel ratio
(too much air) results in poor ignition.
16
In Summer the Sun is brighter. It is more intense and so more effective at splitting
up oxides of nitrogen. This leads to the formation of ozone.
17
Rush hour traffic in the morning releases the chemicals needed to produce the
smog. However, the energy from the sunlight to bring the reactions about, does
not reach its peak until around midday when the sunlight is most intense.
18 a) Carbon dioxide is not toxic and does harm local air quality.
b)
Carbon dioxide is a global pollutant contributing to the greenhouse effect and
climate change.
19
The distributions predominantly reflect centres of population and industry.
20
Emissions of PM10s has declined markedly. There have been significant declines in
all sectors apart from agriculture and waste, industrial processes and road
transport.
21
Nitrogen dioxide – near power stations, in large cities, adjacent to motorways,
next to incinerators and steel works.
Carbon monoxide – near motorways and in large cities.
22
The commercial, residential and institutional contribution has fallen the most. The
contribution from public power has fallen significantly too. Factors such as
boosting efficiency and reducing waste bring about a reduction in the usage of
fuels and hence of PM10 emissions. The use of coal in power stations has
declined. Improvements in diesel fuel and the design of diesel engines has helped
to cut the emissions from road transport since the 1980s.
23
1970: 8%
2004: 23 %
24 (a) It could be a ‘one-off’ high reading caused by a particularly poorly tuned engine
on a lorry, or one taken at a time when few vehicles are in use (Christmas Day).
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The wind direction might be blowing pollutants away from the detector. The
extent of pollution may vary with height above road level.
(b)
They can take lots of readings and average them, so reducing random errors. They
can also check the readings with another instrument and confirm the data if the
readings agreed. They can also check the calibration of the instruments used to
ensure that the readings are accurate.
25
It is likely that the mechanism of sampling would cause the largest errors due to
factors such as:
(i) the position of the detector having an effect – it might be shielded from
pollution or be at a place where air movement is minimal and so pollution
maximised.
(ii) depending on the device used to detect and measure, there might be
absorption of pollutants on the walls of the inlet tube, or reactions between
pollutants en route to the detector.
Analysis of the results is more likely to be mechanised, or through a standard
technique, and so is less likely to produce errors.
26
They would probably be most reliable from a power station which would come
under statutory controls and monitoring. Similarly for a number of industrial
processes where there is potential for pollution of the environment. Estimates for
vehicles with diesel engines are likely to be the least reliable, varying for different
vehicles, being dependent on age, size, and maintenance and so on.
27 a) Graph (b) appears to give a strong correlation as one could draw a line through the
‘points’. Graph (a) has cities H and T off-line.
(b)
The two graphs do show that there is a strong tendency for the Death Rate Ratio
to increase with increase in the concentration of particulates.
28
The findings were a potential threat to the energy and transport industries. The
findings could be used as evidence to support stricter regulation of emissions
which some might want to avoid.
29
Monitoring the health of a group of people for 20 years is very hard to achieve.
Keeping track of all the people is difficult. It is also hard to keep the team of
researchers together and to maintain funding for the research, which is expensive.
30 a) The key point here is that we breathe in from the atmosphere so what pollutes it
has the potential to pollute us. The pollution does gradually disperse or get
washed from the atmosphere by rain but in city streets it can be contained
concentrated so that it reaches hazardous levels.
b)
The particulates must build up to some extent, then get breathed in or fall to the
ground or into the sea. They have not disappeared. Similarly the various gases do
not disappear, though they may be absorbed or react to form something else e.g.
SO2 and NO2 can both combine with water and oxygen to form acid rain.
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c)
Wind disperses pollutants. Rain washes some pollutants from the air. High
pressure conditions mean little wind and this can trap pollutants so that they build
up to unusually high levels.
31
Looking at the elements involved in figure 3.20 it is seen that those coming from
the engine – carbon, oxygen and nitrogen – also emerge into the air – but
recombined to make new chemicals that are less harmful to health.
32
The catalyst used in a car exhaust system only works properly when hot. On a
short journey it is unlikely to get hot enough to do its job properly.
33
Power supply
Advantages
Disadvantages
Petrol engine
Proven technology.
Reliable. Powerful so fast.
Fuel widely available. Long
range.
Use of fossil fuel which is
becoming increasingly
expensive. Emission of
carbon dioxide.
Electric motor
No emission of air
pollutants by the vehicle.
Limited range. Limited
power. Charged by
electricity from
conventional power
stations.
Hybrid engine
No emission of air
pollutants by the vehicle
when running on battery.
Benefits as for petrol
engines outside towns and
cities.
Less fuel-efficient overall.
Expensive because of the
need for two power
sources.
Fuel cell (hydrogen)
No emission of air
pollutants by the vehicle.
Technology not yet fully
developed. Lack of
widespread supply of fuel
(hydrogen). Fuel still
derived from fossil fuel.
34
Currently electric vehicles are charged with mains electricity. The pollution, if any,
comes from the power stations. If charged at night, much of the base load comes
from nuclear power. Nuclear power has relatively low emissions of greenhouse
gases. However the power may also come from gas/oil fired power stations or
from renewables such as wind turbines.
35 a) and b) Many factors reduced the amount of walking and cycling in this period: the
relatively low cost of private transport, the increased perception of the dangers to
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pedestrians and cyclists (especially children), the design of towns and cities to
make motoring easier and walking or cycling less attractive.,
36
This can simply be answered by comparing the lengths of the horizontal bars for
each form of transport in figure 3.24.
a)
Train and bus.
b)
Aeroplane
c)
If the car is carrying more than just its driver.
37
The problem here is that the mass of the driver and passengers is relatively small
compared to that of the car. Most cars have a mass of around 1000 kg. The
average mass of a person might be around 85 kg. So most of the fuel is being used
in moving the car and not its occupants. Also, much of the power of the engine is
used to overcome the air resistance and rolling resistance of the tyres as the car
travels along.
38
There is an energy cost to creating the materials and manufacturing any vehicle. It
takes a lot of energy to create trains, buses and aircraft. Therefore having them
last longer reduces their rebuild energy costs and hence their lifetime fuel costs.
39
The smaller and lighter car would need less fuel and so that should reduce
pollution as long as (i) their numbers did not increase and (ii) their engines were as
efficient or more so than currently.
Having electric cars really moves the source of pollution from where the vehicle is
used to the power station. As most power stations are built away from towns and
cities, this would be practicable, but it has only replaced petrol/diesel pollution by
other forms – coal, oil, nuclear-based – until such times as wind, solar, wave etc.
become significant.
40
At the time of writing, there had been a fair amount of protesting about the high
cost of fuel and the taxes on fuel and on cars that are ‘gas guzzling’. Many of those
living in country areas without public transport complain at their specific situation.
There is also resistance to any extension of congestion charging.
Common arguments to not bring in controls might include such matters as:
 They might make the business uneconomic.
 They may cause closure or promote redundancies.
 Other countries do not have such controls.
 They may make the business less competitive.
41
Water is a liquid at room temperature. It is a compound of hydrogen and oxygen
which are both gases. Water does not burn. Hydrogen burns brightly in oxygen to
make water.
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Methane (in natural gas) is a colourless gas. It is a compound of carbon (a black
solid) and the gas hydrogen.
42
Motoring harms health (giving out gases that pollute urban air) and the planet
(giving out carbon dioxide that enhances the greenhouse effect and causes
climate change). Motoring uses up scare resources: the fossil fuel that is a nonrenewable resource. Extracting and processing crude oil to make fuel can cause
environmental pollution at every stage.
43
Mechanical: high pressure in an engine cylinder presses down on the piston which
drives the wheels through the crankshaft.
Thermal: the energy from the hot cylinder transfers to the cooling water
circulation round the engine, then the hotter water is cooled by cold air flowing
through the radiator.
Electrical: the battery supplies the energy to turn the motor which starts the
engine running; the alternator generates the electricity to provide power to the
lights and other electrical components.
Radiation: the hot filaments in the headlamps radiate light to illuminate the road
at night.
44
Widespread use of catalytic converters is probably not a long-term solution as
they do not in fact reduce CO2 emissions at all; indeed they probably increase
them slightly as more fuel is consumed overall. The solution seems more in finding
replacements for fuels that cause pollution.
Improvements in fuel and in the design of diesel engines are reducing the
emissions of particulates.
Crucial to the argument is the seriousness of the health effects of particulates and
oxides of nitrogen.
45
Benefits widely shared with a minority suffering the ill effects is a particular
problem for air travel because of the noise and pollution concentrated around
airports. In these circumstances, the interests of the minority can easily be ignored
because of the wider benefits. The situation is not so clear cut with motoring. The
pattern of benefits and harmful effects varies greatly from place to place
depending on how close people live and work to motorways, flyovers and other
places with intense road traffic.
46 a) There are still arguments about the extent to which urban air pollution is harmful
to health. It is difficult to forecast what technology might be available to reduce
pollution in the future. It is also difficult to predict what processes might be
developed that one needs to respond to and the extent to which technology could
deal with them. Similarly, it is difficult to forecast the effects of pollution longterm.
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b)
The social difficulties are likely to reflect the wishes and needs of the population in
terms of jobs, personal freedoms and lifestyles. The political difficulties are in
trying to balance what is best for the nation’s health and what might keep the
party in office. The economic difficulties would include how tackling air pollution
might affect jobs and profitability.
47
Driving less far might be realistic when employment is more local or actually
working from home. Currently far from all jobs can be home-based so it is not
realistic. Some never will be – sales staff who need to show off goods and discuss
matters with potential buyers.
Possible restrictions might include more limited access to towns and cities and
promotion of Park and Ride schemes. Additional road tolls, or even a bar on some
roads, when not carrying passengers. Taxing according to the number of miles
travelled – higher road fund tax for greater usage. Already, insurance companies
are discussing having higher charges for those that use their cars the most – much
like the higher tax suggestion although for a different reason, namely to reduce
their risk.
48
For private cars one could add a tax to petrol or have a variable road fund tax
according to the miles covered. With public transport the cost could be
incorporated in the charge for a ticket.
Why not make the person being moved pay? Should it apply to doctors, nurses,
fire-fighters? Who else might you wish to exempt?
49 a) When choosing an upper limit, the factors to consider involve the health and
environmental effects of the pollution. Also it is necessary to take into account the
various costs of lowering the limits such as the impact on industries that create
wealth and employment, and the value that people put on easy access to various
forms of transport. Even if the lowering of emissions is feasible, it can be too
expensive to be affordable.
b)
The limits have to take into account the accuracy of the methods of measurement.
They also have to take into account that the cost of ensuring a total absence of
pollutants would be extraordinarily high or require a very dramatic change in
current lifestyles.
50
Policy needs to take into account different interest groups in cities and in rural
areas and consider the concerns of elderly people and those with physical
handicaps or other special needs. A powerful but popular policy is to raise the cost
of transport of all kinds. Another approach is to shift the balance of investment
towards forms of getting about that do not involve fuels, so favouring walking and
cycling as much as possible. A shift from private to public transport can cut fuel
use. Congestion charging, bus lanes and investment in new buses and trains can
encourage more people to use public transport. In the longer term, policies can
reduce the need for travel by encouraging people to live nearer to where they
work and by cutting down on the travel for shopping expeditions and so on.
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AS Science in Society
Answers to the questions
Chapter 4 Medicines to treat disease
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Plants vary slightly in their chemical composition. There may be several chemicals
in a plant that are chemically active. Drug developers need to know which
chemical is responsible for any effect. The results of tests are very hard to
interpret if they are based on mixtures of drugs of uncertain composition.
2 a) It is generally impossible to create a drug that cures a patient by interfering only
with the natural processes in an microoganism or in the diseased cells of the
patient’s body. If the drug has any effect on healthy parts of the body there are
likely to be side effects.
b)
Deciding whether or not a drug is adequately safe is a matter of judgement which
involves weighing up the benefits and making sure that they outweigh the risks.
What counts as adequately safe is not the same for a drug to treat a common cold
and a drug to treat serious heart disease or cancer. No drug is without risk, but,
through animal and clinical drug trials, the potential risks and benefits are
measured scientifically.
3
Safety tests to check that the new drug does not harm embryos, fetuses and
babies incuding tests to see if the drug passes through the placenta to the baby’s
blood stream or gets into the mother’s milk.
4 a) and b) Some interactions between drugs and chemical reactions in cells are specific
to a particular species, and even to individuals within that species. Animal models
and computer modelling can give useful predications of efficacy and safety, but
can never predict the full potential interactions between drugs and the human
body.
5 a) Phase II trials normally test the drugs on healthy volunteers so it does these
people no harm to be given a placebo. Patients involved at this stage have given
their consent to taking part in this phase of the testing. Testing is small scale and
short term.
b)
Phase III trials are carried out with large numbers of patients who are ill and need
treatment. It would not be right not to give them any treatment as part of an
experiment. At this stage the aim is to confirm that the dose levels are right and
that there are no undetected side-effects.
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c)
 When there is no known effective treatment available.
 Where the disease is minor.
6 a) In this phase the whole population is made up of all the people with the disease
that the new medicine is designed to treat or cure.
b)
Doctors are likely to be more aware of patients with are more severely ill so that
they have sought treatment or gone to hospital. Some people with the disease
may not have seen a nurse or doctor. They may have sought help anonymously
on-line or from NHS Direct. Also some patients, or their relatives may be unwilling
for them to take part in a trial.
7
The efficacy of the active drug's treatment is the due to its active ingredients plus
any effects of treatment (e.g. placebo effect). The effect of treatment by the drug
is the difference between the active and the natural history groups. This can be
compared with the efficacy of the treatment process alone: the difference
between the placebo group and the natural history group. This is a measure of the
placebo effect. The effect of the drug’s active ingredient is the difference between
the active and the placebo group. The use of a natural history groups allows the
entire treatment process to be compared with the magnitude of the placebo
effect.
8 a) Regulation is intended to ensure that the makers of medicines and doctors do not
sell or prescribe drugs that are ineffective or harmful. Regulation in the UK is also
aimed at ensuring that the NHS gets good value from the medicines it buys.
b)
Regulators have to take into account: the results of drug trials showing the
benefits of the drug in relation to any known side effects, the benefits to patients
compared to other treatments (if any), the cost of the drug.
c)
The MHRA assesses the efficacy and safety of new drugs. NICE carries out costbenefit analyses to see if a new drug provides sufficient value to patients to justify
its costs.
9
Some rare side effects may not become apparent until a drug has been prescribed
on a large scale. At this stage is it not in the interest of the pharmaceutical
company for side effects to become an issue. This makes it important that there is
an independent system for collecting information about side effects from all
available sources.
10
Your answer to this question depends on your experience and the people you
know, if any, that have tried complementary medicine.
11
Your attitude to regulation might be affected by your view on the effectiveness on
the medicines. Arguably, the more effective a medicine, the more important that
it is regulated to ensure that it is not harmful and does not interact in a dangerous
way with other treatments. You could also argue that the public should be
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protected by regulation from medicines that are ineffective. People who very ill
can be so desperate that they waste their money of medicines that are ineffective
or harmful.
12
Some (not all) people with allergies turn to complementary therapies as a result of
dissatisfaction with conventional medicine and because increasing numbers of
people and reports say that complementary medicine works. There are those who
would argue that this is not only wise but scientific - having rejected one paradigm
or theory (conventional medicine), the person switches to another. Others,
though, would maintain that there is little good evidence that complementary
therapies work and that some such treatments may be harmful.
13
Scientists value evidence about drugs the comes from systematic, epidemiological
studies where the results have been published in peer reviewed journals,
replicated by others and subjected to sustained critical assessment.
14
Complementary medicine is intended to work alongside conventional medicine,
whereas alternative medicine can replace conventional approaches.
15
Complementary treatments may involve a relationship between the doctor and
patient which means that it not possible for the whole process to be subject to a
double-blind study.
Where the alternative is a treatment, both patient and doctor inevitably know
whether or not they are receiving the complementary treatment (e.g.
acupuncture) or the placebo (e.g. relaxing massage).
16
Setting up a regulatory system is expensive. It is only worth doing if it is
demonstrably necessary to protect the public from harmful effects of
incompetent/unscrupulous practitioners of hazardous treatments. With
conventional medicine the powerful effect of medicines, the scale of use and their
overall cost means that regulation is judged to be necessary. Our society has
judged that regulation is largely unnecessary for most alternatives while only
limited amounts of public money are spent of complementary medicines.
17
Bias arises if the people who agree to take part in the trial are all particularly
disposed towards the treatment and if those who drop out of the trial are
consistently those who are in some way unhappy or uncomfortable with the
treatment. People may drop out or refuse to take part due to illness, and this
could make it less likely that the results identify capture people suffering effects of
the risk factor.
18
Toxicity testing with animals is used to determine the minimum single dose that
can kill; also the dose which, if taken repeatedly can lead to serious of even fatal
results. These, and other results are used to determine the dose to use in the first
stages of clinical trials. Clearly it is very important to get the results right to avoid
harming the volunteers involved in phase I trials. The approach has to be
systematic so that the work can be replicated if necessary. Also all observations
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and measurements have to be carefully documented so that the outcomes of
administering a drug can be related to the size of dose given. If, at any stage,
things go wrong, the recorded evidence can be used to show whether or not the
procedures have been carried out according to approved protocols. This could be
particularly important if unforeseen outcomes lead to a legal challenge for
damages in the courts.
19
Experience has shown that no animal trials can ever fully predict reactions to
drugs in humans. Even so most people would consider it irresponsible not to carry
out animal studies before human trials, as these studies can indicate toxicity and
efficacy in many cases.
At a cellular level the processes of respiration, growth and cell division are very
similar in all animals but there are many differences in the way that cells are
organised from one species to another. Also the body organs have different
relative sizes in different animals, and the way chemicals are taken up and
eliminated from the body varies between species.
20 a) Systematic sampling is important to ensure that the sample is representative of
the whole population of people that might be treated with a medicine.
b)
Randomisation in the selection of participants to test and control samples is very
important to avoid bias. Randomisation helps to ensure that both types of sample
are representative of age, gender, ethnic origin, social class, life style and so on.
c)
The larger the sample size the less likely it is that the results will be affected by
random variations. With a larger sample it is more likely that results will be
statistically significant. However there are practical limits to the size of samples
used for medical research. These limits may be imposed by cost, the possibility of
recruiting participants to the study and the feasibility in keeping in contact with a
large group of people.
d)
Research designs such as cohort studies and case-control studies include control
groups. The control group usually receives a placebo or the standard treatment so
that the effects of the medicine on the test group can be compared with a
comparable group of people who have not received the new treatment.
21
Possible questions to consider:
 Who has done this research and where do they work?
 Who do the researchers work for and might there be any conflicts of interest?
 How big was the study and were what type of research design was used?
 Has the research been published and if so where?
 Have other expected reviewed and commented on the findings?
 Have the findings been replicated?
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 Who has provided this report – is it from an independent journalist or from
someone with an interest of some kind in the findings?
22 a) The processes of developing new medicines involve testing on animals and
humans in ways that could be open to abuse if not carefully regulated. Powerful
interests are involved in the discovery, production, marketing and prescription of
new medicines. The sums of money involved, the reputations of health
practitioners and the deep worries of sick people mean that there is considerable
scope for misreporting and for the misuse of the resources available for health
care. Also the consequences of mistakes can be very serious for both those who
provide treatments and for patients. There are differences in status between
doctors working on different specialism and some patients are, for various
reasons, in a better position to get the benefits of new treatments than others. So
this is such an intensely political field that governments see the need to regulate.
b)
They have to take into account the efficacy and safety of the medicine as shown
by all stages of clinical trials to see if the drug should be used at all. If the drug
passes the initial tests, the regulators then have to carry out a cost-benefit analysis
to see if the new treatment gives value for money in comparison with alternative
treatments, or alternative uses of the resources for other kinds of health care.
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AS Science in Society
Answers to the questions
Chapter 5 Ethical issues in medicine
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
The answer depends on your point of view. You might reflect on whether or not
your opinion is affected to any extent by learning more about the development of
drugs and the ways that animals are used in research. The important skill here is
being able to recognise where your own ethical arguments fit with the different
ethical frameworks that exist.
2
The organisation defending the use of animals in research is essentially using a
utilitarian argument.
The animal welfare group is weighing up the rights of animals against the rights of
humans while giving greater priority to human rights.
The antivivisectionists put priority on the rights of animals; asserting that it is
unjust to experiment with animals and at the same time making the utilitarian
point that the tests are of no value because the results with animals do not
contribute meaningful results when it comes to the treatment of humans.
3
In planning research experts may be competent to judge whether the design of
the research is one which will answer the question posed taking into account all
the technical issues.
However there are two further questions which must be addressed and these are
not medical or technical issues. The first is one of cost-effectiveness. If resources
are limited should public money be spent on this problem rather than on some
other need?
The second is a question of ethics. If the patient is likely to suffer some pain or
other side-effects in taking part is this justified for the greater good? Is it possible
to gain informed consent, what about research on small children? For the costeffectiveness and ethical issues, which affect the whole society, it is important
that those not involved in the work evaluate the issues and represent the views of
a wider cross-section of the population. They may see the priorities differently
from those who are committed to the research.
4
It is necessary that medicines are tested on healthy people so that side effects are
clear and distinguished from the symptoms of the disease being treated. If people
are to give up time and possibly take risks they should be paid. However payment
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means that some people may volunteer for the wrong reasons. The two groups
who most commonly volunteer are prisoners and students.
5
One approach is for the agencies that buy medicines, such as the NHS, to use their
purchasing power by restrict their choice of drugs that have been tested under
conditions that respect the rights of the participants in trials. Another approach is
for international agencies linked to the United Nations to check up on drug trials
by the big pharmaceutical companies. Investigative journalists can study the issue
and alert the public and politicians to the issue through their reporting.
6 a) Pharmaceutical companies may have little commercial incentive to develop drugs
for diseases that are more common in developing countries, where the economic
situation does not allow a profitable return on medicines sold.
Generic drugs produced by developing countries under license from the drug
companies risk these cheaper versions (illegally) being made available outside the
country with the licence, reducing profits for the company.
b)
Large charitable foundations can intervene and give grants to support the
research into treatments for diseases that it would not be commercially viable for
industrial companies to fund. Similarly government aid programmes could support
research of this kind.
7 a) Similarities: the people affected have limited political influence; income from sales
is not large enough to fund research; incentives are needed to fund the research.
b)
Differences: the diseases in developing countries may affect a large number of
people, but the lack of market is due to the country’s economics. Orphan drugs
are for diseases which only affect a small minority of people. The lack of market is
due to small numbers.
8 a) Clearly sub-standard or ineffective drugs do no good to the patient. With some
infectious diseases they may help to increase the problem of drug-resistance. They
are a threat to programmes designed to eradicate infectious diseases.
b)
The drugs in question are likely to be widely used because they are cheap – and
indeed may be the only drugs available. Governments can help by negotiating with
pharmaceutical companies to make available reliable drugs at affordable prices.
9
The genetic material in the cells of the cloned embryo comes from the body cell.
The donated egg has all its genetic material removed before nuclear transfer takes
place. The ‘parent’ of the clone is therefore the donor of the body cell.
10
Parkinson’s disease and diabetes are conditions which arise because specialized
cells in the body have ceased to produce the chemicals needed for normal health.
The hope is that it will be possible to use stem cells to replace the cells that have
been damaged or destroyed.
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11
If scientists can find what triggers stem cells to specialise into different tissues, it is
possible that, in the future, adult tissue stem cells could be used for therapeutic
cloning in place of embryonic stem cells.
12
While there are serious doubts about the possible effects of stem cells in the
body, the risks are not balanced by the potential benefits unless the patient is
suffering from a life-threatening disease.
13
Pharmaceutical companies are businesses that need to make money through
selling drugs. Their brochures cannot contain misleading material, but they may
emphasise positive features and data over the less positive. Articles in peer
reviewed journals are more likely to be critical, to point out any flaws in methods
used to collect data, or in interpretation of the data.
14
Some people would argue that use of embryos in research is wrong, no matter
what the circumstances, on the basis that the embryo has rights.
A utilitarian might argue that using discarded embryos brings about less harm than
creating embryos for the purpose of research. Whether either is morally
acceptable is a matter of whether the total good coming from the research
outbalances the harm to the embryos.
15
Research on nuclear transfer in humans could, in principle, lead to human
reproductive cloning. An embryo created by nuclear transfer may have the
potential to develop normally if implanted in a uterus. Some people argue that
technology which is open to such abuse should not be licensed.
Other ethical issues include the informed consent of the egg and body cell donors,
and any harm that may come to women who are treated to produce multiple eggs
for donation.
16
A 14 day human embryo is not recognizably human, or even recognizably animal.
It is just a tiny group of cells which is about the size of a typical printed bullet
point.
17
Before 14 days there is no possibility of the embryo suffering by any definition.
There is not even a rudimentary nervous system in place. This is also the time up
to which twinning is possible, so up to 14 days it could be argued that the embryo
is not necessarily an individual. (It would be ideal to use quotes from e.g. the
Warnock report in this answer).
18
The issues here are mainly to do with informed consent; permission would need
to be given for any type of future research, and to use the genetic line to create
cell lines or embryos for research or therapies. As future types of research are
unknown, people would be giving consent for unknown actions.
Review questions
19
Ethical questions relate to values, they ask questions about whether or not things
should be allowed to happen, and weigh up the risks and benefits for individuals
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and society (Should it be done?). Science gathers data through observation and
experiment and seeks explanatory theories to account for patterns in data.
Scientific knowledge explores what is possible (Can it be done?). Scientific data
can be used to provide information about risks and benefits which can inform
ethical arguments but not provide the final answers to questions that are not
scientific.
20 a) A doctor might not want to avoid telling a patient that they have a terminal illness
such as cancer. Also a doctor might want to delay telling the mother of a baby that
there are signs which suggest that there is something seriously wrong with the
baby.
b)
A doctor has to judge a situation, and decide how much information a patient will
benefit from. In some cases, the truth about a patient’s condition may not be
certain, and the way the truth is delivered often changes the way it is received.
Some patients express the wish not to know the truth, and this is considered a
right. Telling the truth to patients is part of respecting them and allowing them
autonomy. Patients have a right to informed consent, and this must include
disclosure of any information condition or treatment they are involved in. Studies
have shown better recovery rates or pain relief in patients who were given
information about their condition and treatment.
It is difficult to imagine a situation where lying would be an ethical option, but if
the truth may cause distress or harm, this has to be taken into account when
considering timing, support and counselling of patients who have received bad
news.
21
The egg involved in nuclear transfer has no nucleus, so none of the genetic
material found in chromosomes. The resulting cell and future embryo only has
nuclear genetic material from one parent. This material comes from a donor body
cell, so the embryo’s genetic parent is the body cell donor.
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AS Science in Society
Answers to the questions
Chapter 6 Reproductive choices
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Otherwise the amount of genetic material in each body cell in each generation
would double, since each generation starts with the fusion of two sex cells to form
the fertilised egg (the first body cell) from which an individual develops.
2
There are several forms of gene responsible for CF. There is one normal form and
several forms that are faulty. The child inherits one version of the gene from the
mother and another form from the father. Only one of the two inherited forms of
the gene need be normal for the child to avoid CF. A carrier has one normal form
and one faulty form of the gene. A person who is healthy and not a carrier has two
normal versions of the gene. In the family in question, one parent has two normal
versions of the gene and so any child will have at least one normal form and so
cannot be affected by CF.
3
One in 25 people, in a white population, carry the faulty gene. The chance that
both parents will be carriers is 1 in 625. Only 1 in 4 children inherit two recessive
versions of the gene and get CF. So that is 1 in 2500.
4
If the baby lives to old age there is a probability of 50% (i.e. 0.5, equals a half) that
it will develop Huntingdon's disease. Babies themselves are never affected by
Huntingdon's disease as it only develops in adulthood.
5
Many people prefer to enjoy the years of healthy life in ignorance of any inherited
certainty that they will suffer from the disease in middle age. Once one family
member knows their genetic status in relation to Huntingdon’s, this affects all
their offspring – whether a positive or negative result. This responsibility to future
generations is what drives some people to discover whether or not they have the
Huntingdon’s gene, but other people find the responsibility of passing on the news
to young children or teenagers difficult to bear.
6 a) If your relative who has heart disease is a woman this information predicts that
your own risk of heart disease is nearly three times the average. If your relative
with heart disease is a man then this indicates that your own risk is not quite as
high at 2 to 2.5 times the average. (In either case your risk is higher if you are male
than if you are female).
b)
The effect is quite marked whether the relative with heart disease is male or
female so it is unlikely to be directly sex-linked. More details of the exact pattern
of inheritance would be required before reaching any conclusions.
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7
 tumour – a growth or swelling formed from abnormal division of cells.
 benign – the growth may cause damage if it gets too large, but will not spread
to other parts of the body.
 malignant – the tumour is capable of spreading to other parts of the body
where further cancerous growths might occur.
8
Normal body cell
Cancerous cell
Processes in the
cytoplasm
Respiration and other
processes happen as
normal
Respiration and other
processes happen as
normal
Extent of differentiation
Differentiated into skin,
nerve, muscles and other
cells
Undifferentiated
Genetic material in the
nucleus
The DNA is largely as
inherited. This may
include genes that
predispose individuals to
particular cancers
DNA largely the same as
other cells but with a
number of additional
mutations
Cell division
Some cells do not divide at
all, others divide in a
controlled way to replace
cells lost by wear and
injury
Uncontrolled cell division
gives rise to a growth of
undifferentiated cancer
cells.
Tendency to break away
and spread to other parts
of the body
No tendency to spread to
parts of the body where
they should not be found
Tendency to spread and
form further colonies of
abnormal cells in other
parts of the body.
9 a) The absence of error bars on the chart means that it is not possible to decide if the
differences between the cancer rates for the various groups of people is
statistically significant. However the much higher death rates between the native
Americans on the one hand and the white and African American populations on
the other does suggest that different ethnic groups differ in their tendency to
develop breast cancer.
b)
The observed differences in incidence and mortality of breast cancer between the
different ethnic groups could be due to differences in many cultural and
environmental factors including:
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 lifestyle including diet
 socio-economic group
 awareness and uptake of screening
 attitudes to health and use of heath services.
All these factors could affect risk of breast cancer, and the different ethnic groups
may have different degrees of tendency for one or more of these indirect risk
factors.
10 a) If the human fetus has a right to life, it can be argued that those responsible for its
welfare have a duty to ensure that it lives and lives well. This might mean that a
pregnant woman has a duty not to smoke cigarettes, consume large amounts of
alcohol or undertake other potentially harmful activities. Similarly, the woman,
the father, medical practitioners and society in general can be argued to have a
duty to ensure that the woman and her unborn baby receive enough food, have
decent housing, access to medical care and so on.
b)
This can arise if the growing fetus is, in someway, a threat to the health and
wellbeing, or even survival, of the mother. In these circumstances the women’s
partner and family should be involved in the discussions as well as doctors.
The 1967 Abortion Act says that, subject to the agreement of two doctors,
abortion is legal up to the 24th week if the continuance of the pregnancy would
damage the physical or mental health of the pregnant woman or the continuance
of the pregnancy would injure the physical or mental health of her existing family.
Abortion is allowed after 24 weeks gestation if the pregnancy represents a risk to
the woman's life, or grave, permanent injury to her health, or if there is
substantial risk of serious fetal abnormality.
11
A false positive is when a test gives the result 'positive' when, in reality, it should
have given 'negative'. Similarly, a false negative is when a test gives the result
'negative' when, in reality, it should have given 'positive'.
12 a) Number of false positives is 9990.
b)
Number of false negatives is 5. (In reality, it is impossible to have a false negative
as high as 5% for a condition that only affects 0.1% of individuals.)
c)
No absolute answer can be given. It depends on the severity of the condition and
what happens to individuals identified as having the condition - for example,
whether they are aborted (as happens with some genetic conditions) or given a
special diet once they are born (as happens with some other genetic conditions).
d)
A false negative means that the baby is not thought to be affected by the
condition detected by the test. The baby is in fact affected and the consequence is
that the baby or the mother misses out on necessary and appropriate treatments.
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e)
A false positive at the very least creates anxiety for the parents. More seriously
the baby might be given a treatment that could be harmful. At worst the outcome
is an unnecessary abortion that kills a healthy baby.
f)
Again, the answer depends on the severity of the condition and the consequences
of any treatments or actions that are based on the test.
13
Because no test is 100% reliable and it is best to consider the possibility that the
result it gives may be false. Understanding the interpretation of test results is part
of being able to give ‘informed consent’ for the test.
14
Ethical issues might include:
 Potential harm to the fetus through carrying out the test.
 Attitudes to disability.
 Rights of the mother versus rights of the fetus (if abortion is being considered).
 Duty of care to the fetus as a result of the fetus’ rights – on the part of the
parents and family, medics and wider society.
 Informed consent when agreeing to the tests – which includes understanding
the implications of positive and negative results, and the possibility of false
positives and false negatives.
Ethical frameworks:
 Utilitarian approaches migth advocate the reduction of genetic diseases in the
population through screening and abortion.
 Rights and duties could refer to the fetus, parents, mother alone or other
members of society.
 Autonomy would address issues of informed consent in relation to the tests.
 Issues of justice would involve exploring whether all groups in society have
similar access to information and services.
15
The chances of a carrier meeting a partner with the same faulty allele is rare, so
you’d only expect to see a recessive disease appearing in one generation.
16
Two cousins have married. The likelihood of close family members carrying the
same recessive alleles means recessive conditions are likely to appear much more
frequently where families inter-marry.
17
Gene therapy involving sex cells affects any offspring and the genetic changes will
be carried over to the body cells of any descendants of the person treated. Gene
therapy for body cells has the potential to relieve the symptoms of a sufferer, but
the changes to DNA will not affect the next generation.
18
Although there are common ethical arguments both for and against gene therapy
involving body cells and gene therapy involving body cells, there are ethical
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considerations that differ. In particular, gene therapy involving sex cells has
consequences that are longer lasting and affect future individuals unable to give
their consent to the treatment. Sex-cell gene therapy could make the way for
‘designer babies’, raising issues about the sort of qualities we value in human
beings.
19 a) Individuals and families benefit from knowing more about their health risks so that
they can make life-style changes or seek early diagnosis and treatment to make it
less likely that they become seriously ill. In time there may be drugs designed to
treat people with a specific genetic make-up.
b)
Disadvantages for the family are a possible increase of anxiety, or even fear,
especially if no treatment is available for the disease in question. Another
disadvantage is that the information could be used by the health service to ration
treatment to those more likely to benefit; also insurance companies might refuse
to provide life insurance or raise the premiums for those with particular genetic
predispositions. Some people might find themselves unemployable as a result of
the results of genetic tests.
20 a) A potential benefit for society is that the total burden of health might be reduced
and the resources of the health service might be used more effectively.
b)
Equally greater knowledge on the part of individuals and families might
substantially increase the demand for expensive treatments. Also there is
significant cost to screening programmes. Screening increases the need for advice
and counselling services to explain the results to people.
21 a) People act autonomously if they are able to make their own informed decisions
and put them into effect.
b)
A screening programme for the population most likely to be affected by the
disease increase the autonomy of individuals by giving the information they need
to decide whether or not to get married and then whether or not to have children.
In the Jewish community in question individuals have the support of rabbis and
other members of the community to help them come to terms with the results of
genetic tests that show that they carriers. The tests are manageable and
affordable because of the relatively small number of people involved.
22
There is no treatment for Huntingdon's disease. Screening is offered to individuals
at risk.
23
Justice suggests that if a genetic test is available it should be available to all
whatever their means. Testing the whole population with an expensive test would
draw resources away from other aspects of the health service which can only be
justified if the results of the tests can lead to comparable benefits. The money
available for health care will never be enough to meet the growing demand and so
difficult decisions have to be made. A possible issue with an expensive test is that
it may be restricted to those who can afford to pay.
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The 1 in 4 chance is the same for each child (like the 1 in 2 chance of getting heads
when tossing a coin) – the probability is averaged on large numbers of babies. So
the answers are:
 No
 No
 No
 Yes
 No
25 a) The answer to this depends on people’s opinion about the importance of trust in a
relationship, and whether couples have a right to information that is available
about their partner that may affect their offspring.
b)
There are some jobs, such as being an airline pilot, for which is particularly
important to recruit fit and healthy people. Excluding people from these jobs if
they suffer from well-understood single-gene disorders could well be justified. The
understanding of the genetics of multifactorial diseases will have to be much
improved before less specific genetic indications could fairly be used to exclude
people from jobs..
c)
Mental illness is a disability in the same way as other physical conditions, and
people should not be discriminated on such grounds. By law, there are some jobs
where medical criteria for employment can be defined. This is very different from
discrimination on the grounds of a risk of an illness. Long term scientific
investigations are team efforts and it would be normal for the composition of the
team to change during the life of the project. Here seems no justification for
excluding someone who might have the potential to do excellent work for 20
years or more.
26
The test is virtually risk-free for the fetus and mother, so high risk individuals can
be identified for consideration of the further tests. This reduces the number of
pregnancies at risk from amniocentesis and CVS.
27
It could be argued that a just system would mean everyone had equal access to a
process which decides whether or not the tests are relevant to them. Justice could
mean everyone has equal information and support to help them decide. Justice
need not mean everyone has access to all tests, because the health service may
then not be able to offer tests to individuals who are most at risk. Currently,
access is unequal across different geographic regions, and often people who can
pay for tests have more access.
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AS Science in Society
Answers to the questions
Chapter 7 Radiation: risks and uses
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Any three sources such as those illustrated in figure 7.2. Examples include visible
light from a light bulb, infrared radiation from any sort of heater and gamma rays
from a radioactive element.
2 a) Infrared radiation
b)
Possibilities include:
 Radiowaves for radio broadcasting
 Microwaves in telecommunications
 Visible light in many kinds of signalling
3 a) Young people are still growing so they have a higher level of cell division than
older people. If the radiation disrupts cell division this is more likely to be harmful
for younger people. Also if some of the biological effects are delayed, young
people have longer to live and so are more likely to be affected in time.
b)
It is unethical to experiment on children in ways that might affect their health and
well being. However, with suitable safeguards about data protection, it is
permitted to collected data about the way a sample of children use mobile phones
and to monitor their health over a period of time.
c)
The advice should recommend parents not to allow unrestricted and unlimited use
of mobile phones. The advice should explain the reasons, emphasising the lack of
definitive scientific evidence about possible harmful effects and the reasons why
the possible harmful effects are more likely to arise in younger people.
4
The precautionary principle applies when there is uncertainty about the extent to
which is technology is harmful. The principle does not mean that the technology
should not be used but that steps should be taken to limit practices for which
there might, in time, be much more definite scientific evidence about the level of
risk.
5 a) Research question: ‘Is there a link between the occurrence of acoustic neuroma
and the number of years of mobile phone use?’
b)
Case control study.
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6 a) Wide range of possible responses along these lines: ‘Cancer risk from mobiles very
low.’
b)
Wide range of possible responses along these lines: ‘Mobile phones will kill you in
the end’; ‘High cancer risk from mobiles after 10 years’.
7
Cancers arise in cells with stages mutations or other damage to DNA (see box on
page 129). If there is time for repair to DNA, then cancer is less likely to develop.
Disrupting the repair processes increases the chance that a cell will go through the
stages that lead to cancer.
8 a) You can find information about the risks from mobile phones at the web site of
Mobile Telecommunications and Health Research Programme.
http://www.mthr.org.uk/
There is advice on this issue at NHS Direct with a number of useful links:
http://www.nhsdirect.nhs.uk/articles/article.aspx?ArticleID=407
The issue is covered by the BBC. Search the BBC web site with the terms: ‘mobile
phone safety’. See for example:
http://news.bbc.co.uk/1/hi/health/6991150.stm
www.bbc.co.uk/sn/tvradio/programmes/shouldiworryabout/mobiles.shtml
b)
The answer here depends on your point of view. The web sites listed under (a)
show you what is known now and what are the main areas of uncertainty.
c)
Ideally one would like to compare results for populations with and without access
to mobile phones but being of similar genetic make-up, lifestyle, eating habits and
so on.
9
For the high voltage power lines the magnetic field varies between 0.5 T and 8
T, and for household appliances between 0.01 T and 20 T.
10
If these magnetic fields are having an adverse influence then keeping the high
voltage power lines 25 m or more from houses seems wise in order to bring levels
down to those of an average household appliance. However, considering that
most household appliances are only for short periods of time, maybe one should
double, treble or even quadruple the distance away. As is common, the decision
depends on your belief in the data available.
11
Ratio of cases to controls with larger magnetic fields is 1 in 6.57 and 1 in 17.59 for
smaller fields. This reveals a ratio 2.68 times as great for the larger fields.
12
Scientists took the Swedish study seriously because of the care with which they
chose their samples, the information collected, and the size of the study.
13
The Swedish study was exploring the possible harm to children from magnetic
fields of varying strengths without proposing a particular mechanism to account
for the effect. The Bristol study was exploring the theory that the effect of the
fields is to ionise the air and concentrate pollutants that children breathe in.
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The pollutants concentrated in the ionised air would tend to drift down-wind. One
might expect the effect on the health of children to be greater on the down-wind
side of powerlines.
15 a) A relative risk shows the extent to which the risk of disease for one group of
people (in this case children living near power lines) if greater than the risk for a
comparable group of other people not affects by the factor in question (in this
case comparable children not living near power lines).
b)
Confidence limits are the limits around an experimental mean value within which
there is a high probability that the true mean lies. There is a 95% probability that
the true mean lies within the 95% confidence interval (which is calculated from
the standard deviation for the data).
16
The results for the Swedish study cover children living within 300 metres of power
lines but they then estimate the strength of the fields to which the children had
been exposed. The English study looks at two groups according to their distance
from the power lines: those living with 200 metres and those living within 600
metre. Both studies looked at leukaemia cases. The English study found an effect
at much lower field strengths than were explored in the Swedish study.
17
There are some interesting web sites on this topic, some showing a particular bias
or vested interest, but not all.
The BBC carried a report on the study by scientists at Oxford published in 2005
and there is a number of links to related reports on the web page.
http://news.bbc.co.uk/1/hi/health/4602315.stm
REVOLT – The Radon Effect in Magnetic Fields
http://www.revolt.co.uk/radon1.html
The Health Protection Agency offers information about electricity sub-stations and
power lines.
http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1158
934607796?p=1158934607796
With the limited evidence you have been presented with it is beginning to look as
if living near high voltage power lines might well increase risk and, with a causal
mechanism having been proposed (although not universally accepted) the links
appear to be getting stronger. However, one could really do with comparing data
collected from a population not having power lines nearby, having a similar
genetic make-up, diet and so on.
18
People are more willing to accept risks they choose themselves.
People are more willing to accept risks when they also gain a real benefit.
Risks which affect a large number of people at one time arouse more concern than
those which happen on a regular basis.
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The media has great influence over people’s perception of risk.
a)
Possible examples: sport especially extreme sports such as rock climbing, smoking,
motor cycling, binge drinking, UV radiation from sunbathing
b)
Possible examples: pesticide residues in food, radiation from radioactive wastes,
food made from GM crops.
19 a) 5.2 per cent
b)
0.35 per cent.
20
People are generally more willing to accept voluntary risks and be more unhappy
about risks that they have little or no choice about. This may lead them to
underestimate the risks of things they choose to do (such as smoking) while
overestimating involuntary risks (such as exposure to cigarette smoke from
others).
21
No activity can ever be entirely free of risk. Where they have a choice, people can
choose the risks which are acceptable to them. Local or national governments
have to make decisions about the level of risk which is acceptable in the society;
for example when setting sped limits or deciding on the safety systems to be fitted
to trains.
22
Cohort studies are expensive to carry out. It is hard to ensure that participants
selected for the study do not drop out and it takes a long time to collect useful
data. (See page 62 in the textbook.)
23
The procedure is illustrated by figure 4.18 on page 62 in the textbook. Members of
the treatment group take 3 g vitamin C a day while the members of the control
group do not.
24
The procedure for a case-control study is described on pages 84 – 85 in the
textbook. The study would be based on one group of people diagnosed as stressed
according to agreed criteria and a control group of people that are not stressed by
these criteria. Both groups would include some who keep pets and some who do
not. The prior lifestyles and experiences of these people would then be compared
to identify possible risk factors for stress, and factors (including pet keeping) that
reduce stress.
25 a) It would be necessary to toss them both very many times to show that the
difference is significant. The more times they were tossed and the greater the
differences between the two sets of data, the more convincing the evidence.
b)
Even if they were tossed many times it is likely that there would still be a small
difference in the frequencies of heads and tails. This might be due to a very small
bias or to chance. It is very hard to prove a negative.
26 a) The report refers to the experience of one teacher who has only been exposed to
Wi-Fi for a short time. It could just be a coincidence that the symptoms started at
the same time as the Wi-Fi was switched on and that they had some other cause.
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The Health Protection Agency offers advice about Wireless Local Area Networks.
http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1158
934607791?p=1158934607791
b)
There is no doubt now about the health risks of asbestos but there is a long time
gap between exposure to asbestos and the development of lung disease. In the
case of the teacher the onset of symptoms from Wi-Fi was immediate. So the
comparison is not strictly accurate. Nevertheless it could be that there are longterm effects of Wi-Fi which will not be clearly established until many people have
been exposed to the radiation for many years.
27 a) (i) To be carbon atoms, the nuclei must have six protons, so carbon-12 must have
six neutrons and carbon-14 eight neutrons.
(ii) To be uranium atoms the nuclei must have ninety-two protons. So Uranium235 must have one hundred and forty-three neutrons and Uranium-238 one
hundred and forty-six neutrons.
b)
They are isotopes as they have differing numbers of neutrons in their nuclei but
are the same element. Isotope comes from the Greek words ‘iso’ meaning ‘same’,
and ‘topos’ meaning place: hence same place in the Periodic Table of Elements.
28
It gives off radiation in the form of a beta particle together with an anti-neutrino.
One of its neutrons changes into a proton.
29
The consequences of infection during surgery are serious and the risk is relatively
high. Irradiation does not cause chemical changes to instruments. The benefits are
clear so long as irradiation is effective.
Irradiation of food can cause changes to the molecules in food that affect its
flavour. Irradiation could, conceivable, create harmful by-products in food.
Irradiation could be used to cover up for food that has been contaminated by
carelessness or inappropriate storage. There is justification, at least in some
instances, of being suspicious of the use of irradiation for this purpose.
30 a) Gamma radiation.
b)
Alpha radiation.
The key here is that ionisation requires a transfer of energy. Hence radiations that
are absorbed in a short distance, transferring energy sooner, must be more
ionising.
31
Alpha particles would be stopped by almost any thickness of paper or metal foil.
Gamma rays would pass through virtually unabsorbed regardless of thickness.
Only the beta particles would show significant change with thickness and so be
useful in gauging thickness.
32 a) 5%
b)
1 in 20
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33 a) For a 1 Sv annual radiation dose the risk of death is 1 in 20. So, assuming a linear
relationship as in figure 7.24, for 1 mSv (1/1000th of 1 Sv) the risk must be
1/1000th of 1 in 20, namely 1 in 20000.
b)
For 2.5 mSv (1/400th of 1 Sv) the risk must be 1/400th of 1 in 20, namely 1 in
8000.
c)
1/40th of the risk of smoking 10 cigarettes a day or half the risk of a road accident.
34 a) Alpha radiation is absorbed by a few centimetres of air and so its ionising effects
are unlikely to reach us, such devices usually being fitted on ceilings or high up on
walls.
b)
The main risk would be from burning on a rubbish dump which might then put the
Americium-241 into the atmosphere to be breathed in by us. It should not be a
risk to water supplies as it is insoluble.
35
This question should refer to figure 7.26.
Irradiation: use of beta emitter in cancer radiotherapy
Contamination: rainwater leaching radioactive caesium into the soil, caesium-137
taken up by grass from soil, then eaten by sheep, then eaten by people
36
The uranium in the granite rocks in Cornwall is a source of radon.
37
Yes. Over 50% of the total natural radiation dose in the UK comes from radon (see
figure 7.29).
38
Hypothesis: people exposed to raised levels of radon in their homes are more
likely to develop lung cancer.
39 a) Risk of developing lung cancer is about 1 in 80 from an annual dose of 10 mSv
from radon.
b)
There is no simple way of making a direct quantitative comparison. This question
should be ignored.
40
Seascale is near to Sellafield where radioactive materials are processed. There are
low-level releases of radiation from Sellafield. Exposure to radiation and to
radioactive materials is known to cause cancer.
41
Gardner’s findings only applied to Sellafield workers who lived in Seascale but not
to workers who lived elsewhere. The 1999 report showed that overall the risk of
children of Sellafield workers developing leukaemia was no greater overall than
for the whole of the UK. Then Dickinson and Parker showed the chance of a child
developing leukaemia was influenced by whether or not one or both parents came
from outside Cumbria.
42
Further research might seek to:
 identify the virus responsible for the onset of leukaemia and show that the
established population was immune to it but not new comers
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 show that there leukaemia clusters in other areas where there has been
population mixing but where there is no abnormal risk of exposure to radiation
43
Lifetime risk of cancer increases by 1 in 20 000 for every 1 mSv of radiation dose.
Dose from CT scan of pelvis is 10 mSv, increasing risk to 10 in 20 000, or 1 in 2000.
44
The risk of developing cancer as a result of the diagnostic use of X-rays is low.
There are many other risk factors for cancer. There is generally a long delay
between exposure to the risk factor and the onset of disease. In these
circumstances it is difficult to demonstrate a link between the use of X-rays and
the subsequent onset of cancer.
45 a) Gamma rays readily pass through body tissues (see figure 7.23) and can then be
detected by a camera.
b)
The short half-life means that the radioactive isotope decays quickly so that body
tissues are only irradiated for a short time.
46 a) There is no benefit to visitors in being exposed to the radiation that is intended to
cure the patient and so visitors should not be exposed to an increased risk.
b)
The half-life of the radioactive iodine is 8 days so the level of radiation falls by to a
quarter of its initial value after 16 days.
47
Examples of irradiation: CT scans, radiotherapy with X-ray beams or radioactive
sources
Examples of contamination: use of technecium-99 for diagnosis and iodine-131 for
treatment
48
Diagnostic procedures are used with people who may or may not be ill. It is
important to understand the risks associated with diagnosis. Radiotherapy is used
to treat people who are known to have cancer and for whom the short term
benefits of treatment clearly outweigh the longer term risks of harm from
radiation.
49
It is relatively cheap to take steps to lower a relatively high dose. As the dose get s
lower it becomes increasingly expensive to lower the dose further.
50
The application of the principle might be applied separately to existing homes and
to homes being built in areas where radon from the ground is a hazard. It is
cheaper to design and build a home to exclude radon entering living areas than to
adapt and existing home.
According to the Health Protection Agency the most effective way to deal with
radon is to fit a 'radon sump' to a property to vent the gas into the atmosphere. A
sump has a pipe connecting a space under a solid floor to the outside. A small
electric fan in the pipe continually sucks the radon from under the house and
expels it harmlessly to the atmosphere. Modern sumps are often constructed from
outside the house so there is no disruption inside. See this web site:
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http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1197636998
945.
The ALARA principle suggests that proven practical steps be taken to reduce the
exposure to radiation to at least below the action level of an Action Level of 200
becquerels per cubic metre.
51
Employers of staff who work with ionisation radiation and radioactive materials
have to abide by the regulations which include the provision of design of
equipment and procedures to minimise risks, the provision of personal protective
equipment, dose recording and monitoring as well as medical checks.
Radiation doses can be kept as low as possible by using as little radioactive
material as possible, limiting the time that people are exposed to radiation,
maintaining as large a distance as possible from sources of radiation and adding
shielding using lead, concrete or other materials.
ALARA implies that, so ling as minimum standards are met, it is appropriate to
strike a balance between reducing radiation doses on the one hand the
practicability and cost on the other.
52 a) The hazard associated with a radioactive material depends the type of radiation
emitted and the intensity of the radiation. Also significant are the characteristic so
the material which determine how it moves through the body and whether or not
it can enter the human body through the food chain or other routes.
b)
Non-ionising radiation, such a visible light and infrared radiation, does not have
enough energy to turn atoms into ions and break up molecules. Ionising radiation,
such as UC light, X-rays and gamma rays can have these effects and so cause
chemical damage in living tissues.
c)
Radioactivity is the emission of alpha particles, beta particles or gamma rays from
unstable atoms. Radiation dose measure the absorption of radiation taking into
account the extent to which the radiation does damage to living cells.
d)
A source of gamma rays can be used to irradiate food to kill bacteria. There is no
contact between the radiation source and the food.
Radioactive iodine is injected into patients to treat thyroid disease. The
radioactive material enters the body so this is an example of contamination.
e)
Ionising radiations can cause cancer because they can cause damage to DNA
molecules. This can damage genes that control cell division. Uncontrolled cell
division leads to cancer.
53 a) For example, exposure to sunlight increases the risk of developing skin cancer but
not all those who sunbathe do develop this form of cancer.
b)
Case control studies have been used to investigate the possible link between
mobile phones and the development of acoustic neuroma and also the possible
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link between the development of childhood leukaemia and living under power
lines.
c)
It is very difficult to ‘prove a negative’. In complex situations many risk factors are
involved and with some of them there is a very low probability that they will lead
to a harmful condition.
54 a) Examples from the chapter include mobile phones, the national grid to supply
electricity, wireless networks, nuclear power and nuclear medicine.
b)
People tend to think that radiation from nuclear waste is much more dangerous
than sunlight but the risk of death from cancer caused by sunlight is much greater
in the UK than the risk from nuclear waste. About 8000 people a year are
diagnosed with skin cancer and deaths from the disease area about 1800 a year.
c)
Some people worry about the possible risks associated with mobile phones but
nevertheless use the phones regularly. Drivers enjoy the convenience of private
motoring despite the fact that about 3000 people die on UK roads each year and
many more are injured.
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AS Science in Society
Answers to the questions
Chapter 8 Lifestyle and health
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Snow’s hypothesis was that cholera is transmitted in water which has been
contaminated with sewage from an infected person.
He investigated the quality of the water supply as a factor which affected the risk
of catching cholera.
Snow found a part of South London ideally suited to testing his hypothesis. Some
houses received clean water from the Lambeth water company, others received
polluted water drawn from the Thames in London by the Southwark water
company. As the houses were often in the same street the two groups were
matched in other factors which might have been involved. Snow found that the
incidence of cholera was much greater in households which received the polluted
Southwark water. This correlation between water supply and cholera incidence
supported his hypothesis.
2
It may be possible to protect people from the disease through reducing the risk
factors, even if the precise mechanism of the cause of the disease is not known.
Known risk factors also give a lead for further investigation of causes.
3
Lung cancer rates increased at the same time as air pollution from cars increased.
Car exhausts contains toxic chemicals and are inhaled. So there was both a
correlation and a possible mechanism to support the idea of a link.
Figure 8.4 indicates that a connection between lung cancer and motor traffic is at
least plausible, because, although not shown, we know that traffic rose steeply
from 1945 - 1960. However if pollution from traffic did have a significant effect on
the lungs it is surprising that levels of bronchitis stayed constant. (The data in
figure 8.4 are national figures. The connection could be better tested if local
figures were used. It would be possible to compare the rates of lung cancer in
urban and rural regions which would have very different levels of traffic.)
4
The increase in lung cancer deaths only became significant some years after the
increase in smoking. Individuals might need to smoke for up to 30 or 40 years
before they became ill with lung cancer.
5
Doctors responded more quickly than the general public to the early evidence of a
link between smoking and lung cancer. This may have been because they became
aware of the evidence sooner and understood the significance of the data better.
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Some of the more compelling evidence came from studies with doctors and so this
made the information seem personal. Also because they had seen the suffering
caused by the disease and were more frightened of it.
6
At any age the risk of dying of lung cancer is greater, the more cigarettes smoked.
The increase in risk is much greater over the age of 55 and is low for those under
45.
7
 At a younger age, people are relatively healthy and the effects of smoking have
not started to become apparent.
 The risk seems remote for young people whilst the benefits they gain from
smoking are immediate.
 There may be an influence from peer-group pressure.
 Older people are more aware of mortality and choose not to smoke, or give up.
8
In an epidemiological study scientists could compare rates of incidence of lung,
mouth, oesophageal and other cancers to see if there is any statistically significant
difference between users of the different tobacco products.
9
People are exposed to a huge variety of chemicals in the environment throughout
their lives. Very few of these are a direct and certain cause of cancer in the same
way that a bacterium is the cause of cholera. Many of them may increase the risk
of cancer, some by only a small amount. It is almost impossible in most cases to
find control groups where one, and only one, of these factors is different in the
two groups. Because the effect may not appear until many years later it is hard to
collect data on the level of exposure to the chemical.
10
In the absence of an explanation of why smoking caused lung cancer it is possible
to think that the correlation comes about by chance. A convincing explanation for
the link between the factor and the outcome makes the claim for the effect much
more convincing.
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11
A sample of people suffering from cancer of the colon (cases) are compared
with a sample of healthy people. Risks shown as such as dietary factors are
studied to see if they occur more frequently in one group than the other.
12
Working people would not be available at lunch time. Membership of primary
school parent-teacher associations is likely to include people within a certain agerange and socio-economic groups. People currently ill may not attend.
13
People with current and previous illnesses are more likely to be represented in the
sample, so this might reduce the apparent effect of any beneficial factors, and
increase the apparent effect of risks.
14
Environmental factors such as lifestyle, diet, exposure to pollutants, and so on, are
likely to be shared by members of the same family, so may be the cause of
observed patterns in the occurrence of a disease.
15
Isolated populations are likely to interbreed, increasing the chances of two people
with the same rare mutation producing offspring. Disease-linked mutations that
are recessive appear as cases more frequently than would be expected in a large,
non-isolated population.
16
Identical twins arise when a fertilised egg cell divides and separates to form two
embryos. Both embryos inherit the same genes from mother and father because
they arise from the same egg and sperm.
17
Identical twins have the same genes. Comparisons of twins reared together or
apart can help to determine the extent to which genes or environment determine
particular characteristics.
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Non-identical do not have the same genes but they are often reared together in
the same environment. Studies of such twins to also help to determine the extent
to which characteristics are heritable or determined by environment.
18
Cheap air travel from the 1970s onwards, has allowed more and more people to
travel to sunbathe in countries with strong and prolonged sunshine. In the same
period it has been fashionable to have a tan. Depletion of the ozone layer also
causes more UV exposure. There is a delay between exposure and the onset of
cancer. The recent rise in skin cancer follows and earlier increase in the general
exposure to UV from the Sun.
19
The more people are exposed to sunshine, the more freckles, moles and other
pigmented areas there are on their skin. This is the main effect when people are
younger. However exposure to sunlight also affects the activity of the genes that
help to give rise to pigmented areas. So as people get older the genetic effect
becomes more important.
20 a) Members of a particular population may all have a similar diet and be exposed to
broadly similar environmental factors. This can mean that they may not be
exposed to one or more important risk factors related to ill health; in which case
the effects of the risk factor will not show up in a study of the population.
b)
The reduction is risk will not show up in the study if the beneficial factor is not part
of the diet of a significant number of members of the population.
21
The advantage of the EPIC and UK Biobank studies is that the data is being
collected systematically over a long period of time with a large sample of people
that is representative as possible. At the start the researchers do not know which
of the people will be affected by the various diseases of interest. The information
will be collected as it happens and not rely on recollection of things that happened
years in the past.
22
The study is collecting a very large amount of personal data about individuals. It is
important that this data does not get into the hands of wrong people and that it is
only used for the purposes stated when the participants agreed to take part in the
research. The ethics and governance council is needed to balance the possibly
conflicting rights of the participants and researchers, and to ensure ethical
practices in areas such as consent and ownership of information.
23
Using sunscreen may prevent people from taking more effective actions to avoid
exposure, such as covering up and moving into shade. Sunscreens have limited
effectiveness if they have been kept too long and or are not applied correctly.
Sunscreen may be removed by sweating or bathing – and so need to be reapplied
from time to time. Applying sunscreen may be normal behaviour during a holiday
or when engaged in some sports but it may not be something that is so easy to do
in a variety of kinds of outside work.
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24
page 1
The precautionary principle applies in circumstances in which there remains
uncertainty about the scientific evidence but where there is a plausible case to be
made that it would be wise to avoid exposure to particular risk factors. The aim is
to avoid using the absence of clear cut evidence as an excuse for doing nothing.
This seems to apply to the ban on smoking in public places which was designed in
part to protect non-smokers from passive smoking but also to cut down on the
amount of smoking by smokers, by supporting the notion that smoking in public is
antisocial.
25 a) Cancer is a disease caused when the normal control of cell division breaks down.
Cells start to divide in an uncontrolled way. This can be caused by changes to DNA
called mutations. At least two critical mutations in a cell are needed to cause
cancer. However the body has repair mechanisms that can repair DNA so in most
cases mutations do not accumulate and lead to cancer.
b)
Risk factors for cancer that cause mutations include ionising radiations, chemicals
in tobacco smoke, air pollutants from motor vehicles and some chemicals present
in the diet.
26 a) For many years, the manufacturers of cigarettes used the argument that there
was no proven causal link between smoking and lung cancer to argue that
smoking should not be restricted just because there was a correlation between
the rise in lung cancer and the rise in smoking.
b)
Scientists have studied the chemicals in tobacco smoke and shown that they can
cause mutations in the genes that control cell division and in genes connected
with the repair mechanisms that help to prevent cancer developing.
Understanding these connections helps to convince scientist that there is a causal
relationship between smoking and lung cancer.
c)
An example is the development of nuclear power to generate electricity. The
highly radioactive materials involved are hazardous and can lead to cancers and
other ailments if the radioactive materials are not contained. Also the medical
technologies which use radiation for diagnosis and treatment (see chapter 7) bring
benefits but also expose patients to radiations that can be harmful.
d)
The larger the sample size, the less the danger of random variations giving rise to
misleading results. The large-scale UK Biobank project is an example of a very
large scale study to explore the relationships between genes, environment and
health.
e)
This is well illustrated by the possible risks from mobile phones and living near
power lines described in chapter 6. The occurrence of harmful effects is so rare
that even quite large-scale epidemiological studies can fail to produce definitive
findings.
f)
The advice that parents should limit the extent to which their children use mobile
phones is an example of the precautionary approach. There is still considerable
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uncertainty about how harmful mobile phones really can be for young people but
it is nevertheless plausible that excessive use of theses phones could be damaging.
27 a) In many countries the mortality rate is higher for women than men.
With Sweden, Denmark and Finland near the top of the list and Greece, Cyprus,
Portugal and Spain near the bottom there is a hint of a trend towards countries in
higher latitudes having higher mortality rates than countries nearer to or in the
Mediterranean. However there are many exceptions to this simple pattern which
may also be related to the extent to which people who mainly live further north
are able to travel to enjoy sunshine in summer.
b)
It could be due to skin pigmentation varying between the countries - there could
be a related genetic component with people who come from families that have
always lived in the more southern countries being naturally better protected
against melanoma.
Perhaps, at least in some countries, women enjoy sunbathing more and are
keener on getting tanned.
Maybe people who are not exposed to intense sunshine for most of the year are
more inclined to expose their pale skin to intense sun when possible and
especially on holiday.
Exceptions to the general trends could be the result of movements of people
between different parts of the world, but arise because people in some countries
have more interest and freedom to travel to hot sunny countries for sunbathing.
Other possible variables are:
 the extent to which men and women in different countries work outside in
occupations such as agriculture
 the scale and effectiveness of educational programmes and promotional
campaigns encouraging people to protect themselves from sunlight
 cultural attitudes to sunbathing and tanning.
c)
Primary schools could explain the reasons for being Sun Smart and then insist that
children follow the guidelines when they are out of door during the school day.
Schools could extent the guidance to parents too and encourage parents to set a
good example at open-air school events.
d)
You could make you argument either way depending on your observations of the
extent to which acquaintances, friends and family respond, in your experience, to
education programmes and promotional campaigns.
28
Variations between studies could arise because of differences in:
 research design including sampling method, identification of controls and
sample size
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 the country or region where the study was carried out
 the types of sunscreen used
 the timescale over which the study was carried out
 the way that melanoma risk was carried out
 the organisation doing the work and the source of funding.
29 a) Examples include: diet and eating habits as well as other more or less social
activities such as smoking, drinking and other types of drug taking.
b)
This might include behaviours that become habitual such as cleaning teeth,
washing hands also some ways of taking exercise in a regular way.
30
You might defend the course of action on the grounds such as:
 this is response to the wishes of consumers
 this is a wise precaution given the uncertainty about safety of some permitted
colours – especially for children who are unlikely to attend to food labels
 customers who do not like the decision can go elsewhere.
You might oppose the decision on grounds such as:
 this is irrational because the scientific evidence suggest that the permitted food
colours are safe
 consumers should be able to make their own decision based on information on
food labels
 it is not necessarily the case that natural colours are safer than manufactured
colours.
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AS Science in Society
Answers to the questions
Chapter 9 Evolution
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Darwin saw that:
 fossils resemble animals now alive but often differ from them
 the creatures on the Galapagos Islands were similar to, yet distinctly different
from, species on the mainland and, in some cases, from species on other
Galapagos Islands.
b)
He thought that the passage of time might allow species to diverge in form and
appearance by evolving from their ancestors. He suggested that an ancestral
animal reaching the Galapagos Islands from the mainland could then evolve
independently on each island to give rise, in time, to distinct species.
2 a) All individuals would be equally likely to survive and reproduce.
b)
There would be no connection between which individuals did best in one
generation and which in the next.
c)
No one type of individual would do better than any other.
d)
Some evolution might be possible but it would happen much more slowly because
most genes would pass from one generation to the next.
3 a) [Lamarck] Birds of prey need to fly fast to catch prey. Over their life-time, birds
develop the appropriate large flight muscles and other key features and pass these
on, at least to some extent, to their offspring. Over the generations the birds
evolve the ability to fly very fast.
[Darwin] Birds of prey need to fly fast to catch prey. Within a bird of prey species,
some individuals can fly faster than others. These birds catch more food, do better
and leave more offspring. Such offspring, at least to some extent, inherit their
parents' abilities. Over the generations the birds evolve the ability to fly very fast.
b)
A blacksmith with highly developed muscles (etc.), does not necessarily give birth
to children with the same attributes.
5 (i) Since these travellers are pre-historic there is no record of existence. In the
absence of any evidence, this is not a scientific statement. It cannot be falsified.
(ii)
This could clearly be falsified by finding an example of a tortoise that was able to
swim from one island to another. It would be necessary to check rather carefully
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that there had been no human intervention if one found a tortoise, today, on an
island where it would not normally be expected to be seen.
(iii) This could, in principle, be tested by experiment – and falsified - but it would be
wrong to upset the natural ecology of these unique islands in this sort of way.
(iv)
This would be difficult to falsify because the islands are volcanic and relatively
young on geological timescales so there are likely to be few, if any, traces of early
organisms that could be carbon-dated to establish their age.
6
They were both alive at the same time and grew up in the same country with
similar cultural influences; both taken part in expeditions overseas and had come
in contact with a tremendous diversity of species which they sampled and
collected; both had read Malthus.
7
Darwin’s theory required the Earth to be very old to allow time for evolution to
create new species. If the Earth was only 100 million years old, this would not
leave enough time for evolution to have produced all the observable diversity of
life
8 a) Darwin accumulated a great deal of evidence through collection through
observing living species today and through experiment. He marshalled his
evidence to show it supported his theory of natural selection. The theory seemed
very powerful. It is often the case that, as a theory develops, some counter
evidence is emerges – but this has to be tested and explored before the new
theory is modified or rejected. Darwin’s argument seemed, to him, too strong to
be overturned by a calculation which might, in time, turn out to be wrong.
b)
Neither Lamarck nor Darwin had access to evidence for the precise mechanisms
for evolution. More recently, natural selection has been supported through
explanations involving understanding of molecular genetics in addition to new
fossils. At the time, with the available evidence, both theories could have been
considered plausible.
9 a) A scientific theory is testable, and it is possible to support or refute it through
evidence from observations or experiments (empirical evidence). Scientific
theories are refined (or replaced) when new evidence arises. Religious beliefs
depend on faith, not evidence, and are based on scriptures, dogma, rules of the
religion or personal experiences which cannot be proved wrong.
b)
Evolution is supported by experiments on fossil evidence, genetic evidence and
observation of living organisms.
Creationism and intelligent design are based on specific interpretations of ideas in
religious texts, and are not open to being falsified by evidence. Creationism is
attractive to people who cannot imagine that chance variation and natural
selection could give rise to complex structures such as the human eye.
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10
Creationist beliefs reject the idea that everything can be explained through
science without any reference to some sort of creator that intervenes in the
development and behaviour of life on Earth. Faiths of this kind can embrace
evolution and much of the evidence for it, but not the idea that conscious human
beings, and other complex organisms, came into existence through chance
variation and natural selection over millions of years. Faith of this kind might be
put in doubt to some degree by further scientific knowledge but, fundamentally, it
is a matter of belief.
11
Creationists put forward detailed, reasoned arguments to support their views. The
arguments are based on different premises to the arguments of scientists. Some
scientists regard the creationist standpoint as irrational, because there is good
scientific evidence to support evolution, and creationists reject it, even though it is
accepted by the scientific community. Scientists take the view that, in time,
natural explanations will be found for any aspects of a theory that are not
understood. They see no need for, or evidence for, any kind of super-natural
interventions.
12
Mendel proposed that the characteristics of organisms are determined by pairs of
factors (nowadays called 'genes'), one of each pair coming from an individual's
mother and the other from its father. His data were collected from successive
generations of plant breeding experiments in whih he recorded such things as the
heights of pea plants and the mothers and fathers of particular pea plants. His
model for inheritance involved things like factors which, at the time, were
invisible, but helped explain his observations.
13
Fast breeding organisms allow scientists to study many generations over a
relatively short time-span, to see if any changes in the genetic make-up of the
population take place.
14
Nowadays there is far more evidence for Mendel's ideas than when he was alive;
it takes people, including scientists, time to get used to new ideas. When new
theories conflict with well-established explanations, such as the 17th century
homunculus theory of inheritance, scientists are often reluctant to reject the
original theory, even when evidence is shown to support the new theory. As new
theories become accepted they are redescribed in textbooks and popularised in
the media. Nowadays genes are a part of popular culture.
15
Climate change puts an environmental pressure on populations to evolve. Some
individuals possess mutations which mean they are better able to survive any
climate (or other environmental) change than others. The offspring of these
individuals may become more common in the population, through natural
selection. This change in the genetic make-up of the population is what can lead to
evolution of new species.
16
Water, space, mates (if same species), oxygen (especially when this is scarce), light
(plants) etc.
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17
It depends on the role of the species within the ecosystem. For example, if a
species is the main food source at the start of most food chains in the ecosystem,
extinction could be catastrophic. If there are many other species which offer
alternative food sources, the effect could be minimal. There may be complex
relationships which make a particular species key to an ecosystem.
18
Evolution only occurs when there is selective pressure, normally a change in the
environment or competition for a scarce resource. Sharks live in the sea, which is a
very stable environment, and has changed relatively little in the past few million
years compared with the land environment. Sharks became highly adapted to
their environment, so mutations would not confer a selective advantage to any
individual showing much variation from the average.
Bacteria treated with an antibiotic are in an environment where there is a great
environmental pressure for evolution; a scarce mutation conferring resistance to
the antibiotic results in selection of bacteria with this mutation, which survive to
produce a new strain. Also - the life cycle of bacteria is very short, a matter of
hours in normal conditions. As mutations are more likely to occur during cell
replication, the more frequently cells divide, the more chance there is of
mutations being present in a population. For this reason, organisms with a short
life cycle are likely to evolve in a shorter time period.
19
In order for a new species to evolve, it must be separated from the species from
which it originates. If the two populations can interbreed, it will not be possible to
accumulate enough differences in genetic make-up to produce a new species. The
deep water between the islands prevents tortoises moving from one to another.
20
The theory of evolution states that over time species have greatly changed. The
theory of natural selection provides one particular mechanism to explain how
evolution may have occurred; the jump between evolution and natural selection
required conjecture and creative imagination.
Other aspects which required this type of conjecture are extrapolating from
Malthus' arguments about the potential insufficiency of human food supply, and
the analogy between selection by nature (natural selection) and selection by
people (artificial selection).
21
Individuals with mutations that allow them to compete successfully for scarce
resources are most likely to survive to pass on their genes. New species evolve
from these individuals that can compete effectively. One way to avoid competition
is to use resources such as food or living space which no other organisms want or
can access. This reduces competition with other organisms living in the same area.
Environmental pressure on species favours evolution which avoids competition
between species, leading to new species specialised to a particular set of
environmental conditions. The number and diversity of different species on Earth
is partly due to environmental pressure and avoiding competition.
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22
page 1
The theory of evolution was based, at the time of Darwin, on observations of the
diversity of life on Earth, and on the fossil record. The theory of natural selection
then suggested a mechanism for evolution, which helped acceptance of the theory
of evolution. Darwin was not the first person to describe evolution. His
grandfather, Erasmus Darwin, explored evolutionary ideas influenced by even
earlier thinkers. However Charles Darwin’s work on the origin of species through
natural selection was new.
23 a) The opponents of the inter-faith alliance were of the opinion that if scientific ideas
are unacceptable to religious beliefs, this makes them untrue. Scientific theories
are only proved ‘wrong’ when evidence is produced which refutes them, or, more
commonly, creates a need to refine the theory.
b)
Most scientific theories can be tested by experiment; others, including evolution
and theories about the origin of the universe are interpretations of different types
of evidence from observation. In these cases, the theories can still be falsified, as
long as it is possible to make predictions that certain types of possible
observations could refute. The theory of natural selection could, for example, be
refuted by finding a fossil human dated from the beginning of life on Earth.
Although, as discussed, scientific theories cannot be proved correct, evidence
from many experiments, or, many different types of evidence that support a
theory do lend it validity.
24 a) This level of variation may be within a single species, or may indicate two species.
This depends on exactly where the differences in the DNA are. Chimpanzees and
humans are different species but have 98.5 percent of their genes in common.
b)
Mules and donkeys are different species, as their hybrid offspring (mules) are
sterile.
c)
An identical genetic fingerprint suggests these are the same species; the colour
difference may be due to a local environmental difference e.g. sunlight or
temperature.
25 a) For the same sort of reasons as Darwin and other contemporaries were slow to
accept evolution by natural selection – the cultural and religious climate of the
time made it difficult to suggest theories which went against literal interpretations
of the bible.
b)
Current systems of classification are based on the relationship between species,
acknowledging the potential for species to evolve into other species. New genetic
evidence means that the understanding of these relationships is growing leading
to changes in classification.
c)
Biodiversity can only be mapped if species can be identified accurately. Both
conservation and exploitation of species relies on identification.
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AS Science in Society
Answers to the questions
Chapter 10 The Universe
1a)
One piece of evidence comes from eclipses of the Moon. The Earth’s shadow on
the Moon looks circular, which means the Earth must either be a sphere or a
circular disc – and the latter is most unlikely as no traveller has ever found the
edge.
The observations by Eratosthenes of the length of the shadow of a stick (p. 155)
are also evidence that the Earth’s surface is curved – as otherwise the length of
the shadow would not change from place to place.
Additional evidence that the Earth is a sphere comes from the fact that if you keep
on travelling westwards (or eastwards) from any point, you eventually come back
to where you started. Magellan’s famous circumnavigation of the globe in 1522
convinced people of his day that the Earth was a globe.
Another kind of evidence comes from observing a ship far out to sea on a clear
day. If you look at it from the beach with binoculars, you will notice that you
cannot see the lower part of the ship’s hull. Only the upper part is visible, perhaps
even only the masts. The explanation is that the surface of the sea is not flat, but
curved (following the curvature of the Earth). So the ship has partly disappeared
over the horizon.
The most direct evidence of the Earth’s near spherical shape is from observations
and photographs from space. Indeed human exploration of space would have
failed had we not been correct in believing that the Earth is a sphere.
b)
Although the observed motions of the stars, and of the Sun and Moon, are
compatible with the view that the Earth is stationary whilst these objects move
around it, the motions of the planets are more difficult to account for from this
perspective. We need complicated models like that of Ptolemy to explain why
Mars, Jupiter and Saturn appear generally to move across the sky in the same
direction as the stars, but from time to time move backwards against the pattern
of stars. This can be much more easily explained if the Sun is at the centre and the
planets (including Earth) are all moving round it. It is also very hard to account for
the phases of Venus, and its regular changes in apparent size and brightness, if the
Earth is fixed and at the centre. And it is hard to explain why the planets Mercury
and Venus are always observed close to the direction of the Sun.
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The stars do not move significantly relative to each other, but appear to move
slowly across the sky in fixed patterns. But the planets move relative to the
pattern of stars. This suggests they are not stars, but something different.
We see planets as circular discs through a telescope and can even (with a powerful
telescope) see some surface detail, whereas stars remain just points of light. This
suggests that planets are a lot closer. Also some planets have other objects
moving round them; Jupiter has moons, and Saturn has rings, for example. We do
not observe any such objects around stars.
3
The fact that they appeared unchanging. In contrast, objects on Earth change with
time. Aristotle also thought that the celestial bodies were all perfect spheres – a
view that was challenged when Galileo observed sunspots, and mountains on the
Moon.
4
The planet’s movement will normally be in the same general direction as the more
distant background stars, as the centre of its circle moves slowly round the Earth.
But the combination of the planet’s motion around a small circle, the centre of
which moves in a larger circle round the Earth, would result in loops in its path –
as seen from Earth. For part of this loop, we would see the planet moving
backwards against the background of the stars (as Figure 10.7 shows). Note,
however, that this model is no longer the accepted one. A heliocentric model
leads to a simpler explanation (Figure 10.9).
5
(i) Ridicule by other astronomers.
(ii) Opposition from the Church authorities.
6
There are verses in the Christian bible which imply that the Earth is fixed. Although
these are widely seen as poetic statements, some people interpreted them
literally and so rejected the idea that the Earth could move. Also, the mainstream
theology of the time was based on Aristotle’s philosophical views, which included
a fixed Earth – making it difficult to oppose or seek to change these, as they were
supported by powerful vested interests.
7
Perhaps the simplicity of the heliocentric model is the strongest argument in its
favour. It seems a much more elegant and satisfying explanation than Ptolemy’s
complex model. Also important is its capacity to explain the retrograde motion of
the planets. It also seems more likely to lead towards an explanation of the cause
of the observed motions.
The most basic argument against is perhaps that the Earth does not feel as though
it is both spinning on its axis and orbiting the Sun at high speed. There is no feeling
of movement, no wind. Also, we do not observe stellar parallax which we would
expect to see if we observe stars at different distances away, on two dates six
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months apart, when we are at very different points in space – at the opposite
sides of the Earth’s orbit round the Sun.
It is impossible to say how one would have decided at the time. It is always
difficult to take up a new theory and overthrow a well established one. The
influence of the Catholic Church was very strong, and its authority was strongly
enforced, so a person needed to be brave to oppose it. On the other hand, the
quest for understanding was bringing up evidence that seemed to challenge the
accepted view.
8
A key observation was a supernova in 1572, showing that the heavens are not
eternal and unchanging. Also Tycho observed a comet whose path would have
taken it through several of the crystal spheres of the Ptolemaic model.
9
Astronomers were still bound to a great extent by tradition and overthrowing a
model established for fourteen hundred years would be difficult to do. They had
worked with the geocentric model and it did have quite good predictive power. It
was not obvious that there were many practical gains from adopting the new, and
unproven, model. And, of course, the heliocentric model is counter-intuitive – the
Earth does not feel as if it is moving at high speed and also spinning on its axis.
10
A key piece of evidence from Galileo’s observations was his observation of moons
orbiting the planet Jupiter. This showed that there were celestial objects orbiting a
centre other than the Earth. (This evidence was in fact available in the 4 th century
BC from the Chinese astronomer Kan Fe.) Galileo also observed sunspots and
mountains on the Moon, showing that these objects were not ‘perfect spheres’ as
Aristotle had declared. So his observations challenged some key parts of the
Aristotelian view. Galileo also made observations of the phases of Venus and
showed that what was seen included a ‘full’ phase which would not be possible on
the Ptolemaic geocentric model. Whilst these observations were in line with the
predictions of the heliocentric model, it was also possible to explain them with
Tycho Brahe’s variation on the geocentric model.
The following web site on Galileo may be of interest:
The Galileo Project at
http://galileo.rice.edu/.
11
This means seeing the model as just a way of doing calculations and making
predictions, but not as a ‘factual’ description of how things really are.
12
It is difficult to be certain. All of us are more comfortable with ideas we have
grown up with, and reluctant to change them especially if they carry religious
significance. Key figures in the Church would also have been concerned to uphold
the authority of the Church from which they gained much of their own authority.
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Galileo’s decision to put some of the arguments of Pope Urban VIII into the mouth
of his character, Simplicio, making these look rather foolish, may have caused
additional opposition.
13
The Dialogue Concerning the Two Chief World Systems is a debate about the
relative merits of the Ptolemaic and Copernican models. It leads to a conclusion in
favour of the Copernican view.
14
Through a dialogue between three imaginary speakers, Galileo was able to present
arguments on one side and the other, supporting and challenging various points in
the way one might in a play, or in a real discussion with other people. The dialogue
format makes it easier to bring out the main points of each argument, present the
evidence for and against them, and put forward and consider possible counterarguments. It is often easier to understand a debate or dispute when it is
presented in the form of a dialogue. Because it was written in Italian rather than in
Latin it could be read by ordinary people, not just by scholars. Perhaps a
disadvantage was that it brought out the arguments too clearly, and showed the
weakness of arguments favoured by some powerful people, making them look
foolish.
15
Kepler used the data collected over many years by Tycho Brahe. The data did not
agree with the Copernican model closely enough to satisfy Kepler, though the
disagreement was tiny and many people would have disregarded it, or assumed
the data were inaccurate. For Kepler, they did falsify the simple Copernican model
– or at least showed it needed to be modified. Kepler did not, however, see this as
falsifying the heliocentric model, which he accepted throughout his life. The model
he eventually proposed was a heliocentric one, based on elliptical orbits rather
than circular ones.
16
That the orbits of the planets are ellipses not circles.
17
No. The word ‘deduced’ implies that only logical reasoning was involved. Others
might have looked at the same data and not come to the same conclusion as
Kepler. It required considerable imagination to consider an orbit shape other than
a circle.
18
Kepler used Tycho Brahe’s data and did not collect more of his own. But his idea
that the orbits might be elliptical enabled him to draw up large tables of
predictions of planetary positions that agreed very closely with observation. For
the first time, a heliocentric model of the solar system had enabled scientists to
make predictions that were better than the old geocentric model.
19
Essentially the problem was: why do objects close to the Earth fall towards the
centre of the Earth, but objects like the Moon do not? Newton wanted a single
explanation that could account for both.
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20
Newton’s Law of Universal Gravitation proposed that there is a force between any
two masses, whose size is inversely proportional to the square of the distance
between them. It can be shown mathematically that the shape of the orbit of an
object round a much larger one, if the force between them follows an inverse
square law, is an ellipse. Also, the statements known as Kepler’s Second and Third
Laws follow as deductions from Newton’s Law of Universal Gravitation. So Newton
provided an explanation – based on a kind of mechanism – as to why the planets
moved in the way Kepler had described.
21
It would have been possible to photograph areas of the sky on different nights and
look for objects that have moved relative to a fixed background pattern of stars.
Before the invention of photography, this depended on having what we often call
‘a photographic memory’. Long exposure photographs can also enable us to
observe objects too faint to see with the unaided eye.
22
This is a matter of opinion. But many people would argue that observing
something without knowing what it is that you are observing does not count as
having ‘discovered’ it. Herschel was the first to see the object we now know as
Uranus and realise that it was a planet.
23
No. It could have meant that the observations were incorrect, and needed to be
done more carefully. Or it could have meant that the predictions based on
Kepler’s model and Newton’s Laws were incorrect, because of some factor that
had not been properly taken into account. This in fact was what scientists
eventually decided was the case.
24
Again, there is no single ‘right’ answer to this. We now see Newton’s Law as highly
trustworthy, but closer to Newton’s time it may not have had such a strong
reputation. Even so, it had impressively explained Kepler’s model, so there were
good grounds for continue to work with it, and look for a less radical way of
resolving the discrepancy between observation and prediction. On the other hand,
Airy could reasonably have argued that Newton simply assumed his Law of
Gravitation applied at all distances, but had no direct evidence that this was so.
(Science more generally is based on assumptions of this kind – that the same laws
apply throughout the Universe, and over long periods of time – for which there
cannot be complete evidence.)
25
He might have looked for a ‘star’ that moved relative to the others around it, from
night to night. Also, after the invention of photography, he might have analysed a
photographic plate which was exposed continuously (except in day time) whilst
being rotated in synchronisation with the Earth. Stars would then appear fixed in
position, but a planet would then show up as a streak on the emulsion.
26
More confident. An apparent anomaly had been explained, by using Kepler’s
model and Newton’s Law. It had led to a new discovery, the planet Neptune.
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Take the separation of the eyes to be 7 cm on average. From s = r where s is the
arc length (here it is 7 cm), r the distance away and  the angular separation of the
eyes in radians 1 second.
There are 2 radians in 360 degrees, one second is 1/360th of a degree, so its value
in radians is 2/(360  360) = 0.0000485. Hence 7 cm = r  0.0000485 rad giving r
= 7 cm/0.0000485 rad = 144385.36 cm or approximately 1443 m.
It would not be easy. The key problems are seeing the eyes at this distance,
resolving them as two separate objects, deciding exactly where the centres of the
eyes are, and finally in having an instrument that can record so small an angle.
28
As radiation spreads from a point source, the surface of the leading wavefront is a
sphere of ever-increasing radius. The surface area of the sphere is getting larger all
the time – so the energy that the radiation is carrying is being spread over a larger
and larger area. The brightness is related to the intensity of the radiation (the
amount of energy it transfers each second to each unit area of an absorbing
surface), so this gets steadily less with distance. So if we have two objects of equal
brightness, the one that is further away looks dimmer, as the amount of energy
our eyes receive from it every second is less, because it has been spread over a
larger total area.
29
If all stars were equally bright sources, this would be correct. But some of the
more distant ones might be actually very bright sources, and some of the closer
ones might not be so bright. So apparent brightness (what we see) may not
correspond exactly to intrinsic brightness (the true brightness of the source).
30
They vary in brightness with time in a regular manner.
There are two useful web sites related to Cepheid variable stars:
Cepheid Variable Stars
http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html
Cepheid Variables as Cosmic Yardsticks
http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/cepheid.html
31
The key was that these stars in the Magellanic Cloud were all around the same
distance away so that the effect of distances on observed brightness was
effectively eliminated. Observed brightness was a direct indication of intrinsic
brightness.
32
No. Shapley had not proved that the centre of our galaxy lay in the direction of
Sagittarius and that the Sun was nowhere near the centre. This was a conjecture
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(or hypothesis) based on his assumption that the centre was where he had found
star clusters forming a huge sphere.
Details of the debate between Shapley and Curtis about the nature of nebulae can
be found on the web site:
The Shapley-Curtis Debate in 1920 at
http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1920.html
33
The appearance of nebulae is such that they could be clouds of gas or dust
relatively close to us or clusters of stars a very long way away. Analysis of the light
from the Orion nebula produces a line spectrum that shows it to be made up of
hot diffuse gas. Other nebulae, called reflection nebulae, consist of dust which
scatters light from nearby stars; so these have the same spectrum as that of
nearby stars. Large clusters of stars have spectra representative of those stars.
Hence spectroscopic analysis provides useful evidence that nebulae are not all the
same kind of thing.
34
The ‘island Universes’ idea is that the Universe consists of many galaxies, each a
kind of ‘island Universe’ (though using the word ‘Universe’ here is a bit of a
contradiction in terms!). The alternative viewpoint was that everything is part of a
single galaxy, the Milky Way.
35 a) Shapley thought that the Milky Way was the Universe – that everything we could
see was part of it.
b)
Curtis thought that some of the nebulae were objects far beyond the Milky Way,
and were in fact galaxies similar to the Milky Way. For Curtis, the Universe
consisted of many galaxies.
36
Hubble’s conclusion about the distance of the Andromeda nebula (now known as
the Andromeda galaxy), and the evidence it was based on, were decisive. The
debate quickly ended – and the idea that the Universe consisted of many galaxies
became accepted.
37
The Andromeda galaxy is estimated to be 2.2 million light years away.
a)
The nearest star (Proxima Centauri) is 4.3 light years away. So the Andromeda
galaxy is 510 000 times further away than the nearest star (or just over half a
million times further away).
b)
1 light year is equal to 9.5 x 1012 kilometres. The radius of the solar system is 4.5 x
109 kilometres, which is equal to 4.7 x 10-4 light years. The distance to the
Andromeda galaxy is about 4.7 thousand million times bigger than the radius of
the solar system.
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Although the points do not lie on a perfect straight line, they do seem to show a
clear relationship between velocity and distance. We also have to bear in mind the
many assumptions made in estimating both velocity and distance, so we should
not expect a perfect straight line. Most astronomers were convinced.
Lots of detail on the Hubble Redshift is provided on the web site:
How Fast is the Universe Expanding
http://map.gsfc.nasa.gov/universe/uni_expansion.html
39
Estimates of both velocity and distance are based on many assumptions; they
cannot be measured directly. One problem that Hubble faced with relatively
nearby galaxies was that their rotations superimposed an additional frequency
shift on to their recessional red shift. He also assumed that the brightest stars in
both nearby and remote galaxies would be of the same intrinsic brightness (i.e.
‘actual’ brightness – not the brightness we observe). But this is not always going to
be a correct assumption. These two factors gave rise to uncertainties in
measurements of both velocity and distance. Hence the graph has points spread
around the best-fit line.
Not everyone agrees with Hubble’s interpretation of the redshift. One who does
not is Halton Arp. His views are summarised on:
Redshifts and the Hubble Law
http://www.heretical.com/science/redshift.html
40
Approximately 140 million light years distant.
41
Explain that the observed red shift suggests that galaxies are receding from us and
so the Universe is expanding. Whilst the analogy is by no means perfect, you could
illustrate the frequency shift of a moving object with sound – a buzzer whirled
round in a horizontal circle give rise to a frequency increase on approach and a
decrease as it moves away. The same is observed when a car with a siren goes
past you.
Note: A common question is ‘What is the Universe expanding into?’. But the
Universe is everything, so there cannot be something else for it to expand ‘into’. It
is space itself which is expanding. There is no ‘beyond the edge’.
42
They observed microwave radiation, coming in equal intensity from all directions,
and corresponding to the electromagnetic radiation that would be emitted from
an object at a temperature of about 3 degrees above absolute zero (3 K). The
eventual explanation of this was that it is the radiation originally released in the
‘big bang’ – the ‘echo’ of the ‘big bang’ if you like.
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43
No, ‘prove’ is too strong a word. (Indeed it is almost always too strong a word to
use about any scientific theory or explanation.) There could be other explanations.
But it had been predicted by calculations based on the ‘big bang’ theory. So
finding it provided strong support for that theory.
44
It has to be seen as a hypothesis. A fact is something that everyone easily agrees
about – and that does not apply to this claim.
45
Observations of distant galaxies suggest that there must be large amounts of
matter (mass) that we cannot see, which are producing the gravitational forces
needed to explain our observations. Scientists called this ‘invisible’ matter, ‘dark
matter’.
46
The evidence for the existence dark matter is quite strong. Gravitation is an
accepted phenomenon, and the account of it provided by Einstein’s Theory of
General Relativity is not under dispute. Also, we know of other forms of matter
(like neutrinos) that are difficult to detect, so the notion of matter that we cannot
observe is not so far-fetched. Dark energy, on the other hand, seems to have
properties very different from anything we know. Gravitational repulsion has
never been observed, and is not predicted by any major theory. Dark matter can
seem rather like a label for ‘something we don’t understand’.
47
Scientists tend to prefer a simpler, more elegant model to one that seems very
complex – and which has to keep on adding further modifications to improve its
match to observation. A good model should be based on relatively few
assumptions. However, it is worth noting that Copernicus’ heliocentric model was
not much simpler than the Ptolemaic geocentric model. Copernicus had to add
extra circles to account for planetary motions. Only when Kepler introduced the
idea of elliptical orbits did the model become truly simpler.
Another reason why scientists might be attracted to a heliocentric model is that it
offers the possibility of explaining the motions observed. Perhaps some force
emanating from the Sun keeps the planets moving along their orbits. The
combination of Newton’s Laws of Motion and his Law of Universal Gravitation
provided this explanation more than a century after Copernicus.
48
No, it cannot be deduced, if by that we mean that it follows logically from the data
collected on planetary positions. These are open to many possible interpretations
and explanations. No one really knows what led Copernicus to his heliocentric
idea. Others, including some ancient Greeks, had had the idea previously, but it
had not taken root. In any case, it required imagination – to envisage how the
motions might look simpler if viewed from a different position, that of the Sun
rather than the Earth. Perhaps Copernicus arrived at his model through a desire to
‘seek the truth’. He may have thought the Ptolemaic model was too clumsy to be
God’s solution.
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49
Whilst we like to have good agreement between observations (data) and
expectations (predictions), this is rarely perfect. Discrepancies might be due to
instrumental error or uncertainty, or the theory on which the prediction is based
may need some refinement, or be incomplete. Slight disagreement between data
and prediction would not normally cause scientists to reject an accepted
explanation; they would be more likely to question the data, or think that there
might be additional factors that had not been taken into account in making the
prediction.
50
This is a historical claim, not a scientific one, so there is unlikely to be complete
agreement about it. In support of it, we might say that the dispute seemed to be
more about protecting one’s position of power and authority than about trying to
determine the truth of the matter. Galileo seems to have antagonised some
powerful people by his way of interacting with them. For example, his decision to
make the character Simplicio, in his book The Dialogue Concerning the Two Chief
World Systems, state some points of view the Pope was known to favour was not
politically astute. Rather than try to find common ground with his opponents,
Galileo often seemed more inclined to ridicule them. On the other hand, there
was a more fundamental issue at stake about the kinds of questions that religion
could address, and those that were the province of science. Galileo on occasions
argued that matters of astronomy were not within the realm on which theologians
should pronounce. The Catholic Church, for its part, was happy for astronomers to
present the heliocentric model as a calculating device that ‘saved the
appearances’, but did not permit them to claim (or seem to claim) that it was a
true description of how things really were. Galileo thought that he had divorced
science from theology, but some powerful people in the Church disagreed. Many
historians think that the real fault line came between Galileo and the philosophers
(including many theologians) who adhered to the Aristotelian worldview. The
Galileo affair was therefore a mixture of elements, and much depended on the
personalities involved. As you may know, the Vatican only cleared Galileo of
heresy in October 1992.
51
The short answer is that both were crucial. Galileo’s observations of sunspots,
mountains on the Moon and the moons of Jupiter were important evidence for his
heliocentric views. Tycho Brahe’s observation of the path of planet convinced him
that planets were not mounted on crystalline spheres. Without Brahe’s very
accurate data, Kepler would never have been forced to give up the idea of circular
planetary orbits. Small discrepancies in the observed position of Uranus led to the
prediction, followed by the observation, of Neptune. However, these data did not
lead automatically or inevitably to the model of the solar system we now think is
correct. Proposing a theory, or model, that can provide an explanation for what
we observe requires imagination and creative thinking. Copernicus, Kepler,
Newton, Adams and Leverrier all used imagination to propose explanations for the
observed motions of planets.
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You might well see them as good scientists, as they did not discard a respected
and valued model, which was in agreement with a lot of other data, without
looking at other possibilities first. It is often sensible to look first for other ways of
explaining an anomaly that have less serious implications.
It usually takes a number of challenges (or anomalous observations) to make
scientists give up well established ideas. An accepted explanation is almost never
rejected until someone has proposed an alternative explanation which deals with
the anomalous data as well as the other known data that the previous explanation
accounted for.
53
Many scientists were convinced of the Copernican model even before Kepler’s
modifications (the elliptical orbits) enabled its predictions to match those of the
older geocentric model of Ptolemy. This suggests that an elegant and simpler
explanation has much appeal – compared to a very complicated model that keeps
being added to, in ways that make it more complex still. Of course, a good match
between data and prediction is also critical – just think of how hard Kepler worked
to get rid of the 6 seconds of arc discrepancy between his predictions of the
position of Mars and Brahe’s data. However, he never seems to have considered
giving up the heliocentric model.
It seems easier to get scientists to accept explanations that do not challenge a
fundamental theory. So, for instance, most scientists quickly accepted Adams and
Leverrier’s explanation for the ‘wobbles’ in the motion of Uranus. This explanation
did not challenge any well-established general theory. Indeed by explaining the
anomaly, it further strengthened the general theory of Newton.
54
There are many examples you might give here. The one mentioned in the chapter
is the Voyager probes. It seems implausible that these would have followed the
path intended if our knowledge of the solar system was not very good indeed.
The making of the first atomic fission bomb in the Manhattan project is another
example. After years of calculation and development of the components, the first
bomb was assembled – and when tested, worked as expected. This suggests that
the understanding of nuclear physics it was based on was largely correct.
Pasteur’s test of the vaccine for anthrax at Pouilly-le-Fort is another good
example. He predicted that a complicated procedure of weakening the microorganism that causes anthrax would lead to a vaccine that would protect sheep
against the disease. When this was dramatically shown in a public experiment in
1881, it provided strong evidence that Pasteur’s understanding of the cause of the
disease was sound.
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Arguments in favour:

It satisfies the basic human trait of curiosity

It is important that humanity keeps pursuing new knowledge.

It provides employment for many people.

From it, a lot of new and useful technologies develop.

It cam stimulate other scientific and technological advances.
Arguments against:
56

The money would have been better spent on health care, education, the
poor and needy, and so on.

Saving the money spent could have allowed a reduction in taxation.

If we want to spend resources on scientific research, then it should be spent
on things that can lead to clear benefits, such as cures for diseases.

Space travel has a huge ‘carbon footprint’ and should be opposed on
environmental grounds.
All are very well established and generally agreed by astronomers. So they come
close to what we normally require to call something ‘a fact’. They are certainly not
guesses, if by that you mean there are no good grounds for considering them to
be true. Some of them may, of course, be revised – the figures might be reviewed.
But it seems unlikely they will be adjusted very radically.
On the other hand, none can be observed or measured directly. Many
assumptions are involved in arriving at all these statements. The evidence has to
be interpreted. So perhaps they should really be seen as hypotheses – albeit quite
widely accepted ones.
They are not ‘theories’. A theory is a general explanation, often based on a model,
that accounts for a wide range of specific events.
57
It is clearly much greater, and more strongly supported by evidence. Just think of
our knowledge of the planets, their moons, the Sun and other stars, other
galaxies, ideas of how the Universe came into being and when, the magnitude of
space – and much more besides. Much of the detail has been established in the
past five hundred years.
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Has this affected how we live? Maybe for some. Appreciating the vastness of
space may make some see our existence as more special, whilst some may take
the opposite point of view, that it seems unlikely we are unique in the Universe.
Most of us find it difficult to appreciate the vastness of the Universe as science
describes it, and the huge span of time since the big bang. We derive our sense of
purpose from events and relationships around us – focusing on the more local.
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AS Science in Society
Answers to the questions
Chapter 11 Are we alone in the universe?
The answers suggested here should not be read as model answers. They are intended to
indicate a possible approach. In some cases, information and comments are included
which go beyond the direct requirements of the question.
1
Extreme conditions: hot dry, desert conditions; very high altitudes where the land
is rocky and cold, in the sulfurous craters of active volcanoes.
2
Possible questions include:
Why has the scientific communities attitude to the search for life on other planets
changed so greatly in the last ten years?
In which aspects of this research are UK research teams particularly strong and
why?
What are the possible benefits to the UK from funding research into this field?
3
There were no particular reasons for keeping the meeting confidential. Science
journalists are good communicators and so can help to translate the language of
scientists into a language accessible to politicians and the wider public. Reports
about the meeting in newspapers and other media could help to tell a positive
story about science and alert people to the work of UK scientists in this field. This
is a topic of wide public interest – but it is not highly sensitive politically.
4
The science minister is responsible to the strength of the scientific research base
in the UK and needs to understand the strengths and weaknesses of UK research
in different fields.
5
This is on a geological timescale in which the Earth is 4.5 billion years old.
6
Scientists are now confident that they can detect earth-like planets around other
stars. They know that life evolved on Earth within the first 0.5 billion of its 4.5
billion year life which leads them to propose that given the right conditions, life
will emerge anywhere in the universe.
7
Mars was once warmer and wetter than it is now and so there is a good chance
that there was once life on Mars. Europa, though icy, has a core warmed by tidal
forces.
8
They are assuming that other life forms have evolved in conditions similar to those
on Earth. So they are assuming, for example, that life will be found where the
conditions are such that water is usually a liquid.
9
See the diagram at:
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http://en.wikipedia.org/wiki/Habitable_zone
or click on Solar System at:
http://odin.physastro.mnsu.edu/~eskridge/astr115/week10.html
The habitable zone lies between Venus and Mars and encompasses the Earth.
10
Spectroscopes can detect and analyse radiation from stars and other objects in the
universe. Different types of spectroscope can analyse light from different regions
of the electromagnetic spectrum. Atoms and molecules interact in distinctive ways
with radiation and this allows scientists to use spectra to analyse distant objects
chemically. Movement of objects causes the position of spectral lines to shift (the
Doppler shift) and so some spectra can give information about the speed and
direction in which astronomical objects move.
11
Living things cannot be seen directly on distant planets. Life is detected by its
effects on the planetary environment, especially the atmosphere. These changes
cannot be detected by land-based telescopes because the related (infra-red)
radiations are absorbed by the Earth’s atmosphere. The light from the atmosphere
of a distant planet is very, very faint and can only be detect by a large array of
telescopes in space.
12
Stars are bright enough to be detected at a large distance by our telescopes.
Planets are invisible at these large distances. However a planet passing in front of
a star can mean that the light from the star gets dimmer, just as the light from the
Sun gets dimmer when it is eclipsed by the Moon. Also, a large planet has a
gravitational attraction for its nearest star. This can be big enough to make the
star seem to wobble as the planet goes round its orbit. This wobble affects the
frequency of the light from the star just as the pitch of a siren on an emergency
vehicle changes as it drives past. Instruments attached to telescopes can detect
and record this change of frequency.
13
The public is interested in stories about life in other parts of the universe. People
are intrigued by the idea of other forms of life. Gliese 581c was the first distant
planet to be discovered which might be in the habitable zone of its star. So this
was an exciting discovery.
14
In the story about Goldilocks and the three bears, Goldilocks tastes the porridge in
three bowls. One is too hot. One is too cold. The porridge in the third bowl is just
right and she eats it all up. Liquid water is a key ingredient for life as we know it.
Gliese 581c was found to be at the ‘Goldilocks distance’ which is not too close and
not too far from its star to keep water on its surface from freezing or vaporizing
away.
15
The Earth rotates and ground-based telescopes rotate with it and so they cannot
be directed continuously at a particular direction in space.
16
The aliens might start by studying the atmosphere of the Earth. Detecting oxygen,
or ozone, would be a strong sign that Earth is an unusual planet since, in the
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absence of life, oxygen quickly disappears from atmospheres. Detecting liquid
water would show that the conditions on earth are not extreme. They could also
detect the various forms of electromagnetic radiation that we use for
communications. The modulation of the signals might indicate that they have
been transmitted as messages.
17
The combination of oxygen, ozone and water with carbon dioxide is a strong
atmospheric signature of a thriving biosphere. In the absence of living things,
oxygen rapidly reacts with other elements and compounds so that it is removed
from the atmosphere.
18
Ministers want to know that the grants, from public money, awarded to scientists
by UK Research Councils are supporting work that is worthwhile, effective and of
international significance. Scientists need to demonstrate the positive outcomes
of their work in order to secure future funding.
19
The answer here is a matter of opinion. You might want to weigh up the chance of
success on the one hand (more likely if the quest is for habitable planets) against
the significance of the findings (which is greater if the research were to detect
intelligent life).
20 a) The discovery of the planet Gliese 5821c helped to validate the predictions made
by scientists about the existence of other habitable planets and the feasibility of
detecting them.
b)
The theorising about life on other habitable planets is all based on scientific
explanations developed from the study of life and the environment on Earth.
Similarly the techniques devised for detecting habitable planets is based on well
established scientific ideas.
c)
The search for habitable planets has only become feasible because scientists have
developed new techniques of investigation such as the various forms of
spectroscopy and telescopes in space. The search for life on other planets is
informed by the work of biologists, earth scientists and others.
d)
Ten years before the meeting described in this chapter, scientists had been very
sceptical about the announcement of the discovery of a planet of the size of
Jupiter. Generally scientists were reluctant to accept that other habitable planets
could be detected, or even that there is life elsewhere in the universe. The search
of intelligent life was not regarded as a part of respectable mainstream science. As
this chapter shows, this has now changed and this type of research has become
accepted.
e)
Some scientific research is conducted for its utility but some largely out of
curiosity. It is in the interest of the UK to be involved in research programmes that
involve telescopes on space satellites because of their significance for advanced
telecommunications. Scientists in this field acquire valuable insight into the
analysis of data. UK scientists earn the right to be involved in projects of this kind
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through their contribution to the development of instrumental methods or of
techniques of data analysis.
f)
The public interest in the possibility of alien life forms means that research to find
habitable planets is reported by the media. So the specialised research that
identified planet Gliese 581c was translated into a popular story by the media with
the help of analogies such as the notion of the ‘Goldilocks distance’.
g)
Civil servants and ministers might find it hard to justify the money spent on this
type of research in the absence of media and public interest.
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