AS Science In Society 1.3 Teacher Notes
Page 1 ©The Nuffield Foundation, 2007
Copies may be made for UK in schools and colleges
AS Science In Society 1.3 Teacher Notes
How Science Works
Aa We can never be sure that an observation is accurate or that a measurement tells us the true value of the quantity we are measuring. A single measurement of anything is therefore inherently risky.
Ab If we make repeat measurements of the same quantity, the values are likely to vary. The larger the number of repeat measurements, the more confident we can be that the mean is close to the true value.
Bc A correlation between a factor and an outcome suggests that the factor may be a cause of the outcome, but does not prove a causal link.
Bd To investigate the relationship between a factor and an outcome, it is important to control all other factors that might affect the outcome. Then changes in the outcome can be attributed to the factor that is being changed.
Bj We are more likely to accept that there is a correlation between a factor and an outcome and much more likely to believe that the factor is a cause of the outcome if we can identify a plausible a mechanism that would link them.
Introduction
This activity is very similar to the sort of questions students will meet in the final exam, though longer. It includes questions on science explanations, on data interpretation and on how science works, reviewing in a new context the causal links ideas met in 1.1 and 1.2.
The activity
This would be more suitable for a class exercise at this stage in the course with the opportunity for discussion where students encounter difficulties. It will take about 40 minutes.
Science explanations
Ed Most matter contains more than one element or compound mixed together. The proportions of the different substances in the mixture will vary. For example the air is a mixture of several gaseous elements and compounds. The proportions of each can be measured in parts per million, parts per billion or other units.
Ee A chemical reaction involves the recombination of atoms to form new and different substances.
Suggested Answers
(a) / (i) / peaks correspond to rush hour traffic / 1(ii) / hydrocarbon + oxygen → carbon monoxide + water
1 mark for each two correct / 2
(iii) /
- nitrogen in air
- high temperature in engine
- nitrogen + oxygen
(b) / (i) /
- sunlight
- air containing oxides of nitrogen
(ii) /
- reaction takes time therefore later than NOx peak
- no sunlight after evening NOx peak
(iii) / 10 ± 1 ppb
1 mark for each value / 2
(c) / (i) /
- No change in admissions up to about 40/ 50 ppb.
- Above 40/50ppb admissions proportional to concentration / positive correlation
(ii) /
- More reliable indicator of ill health than self reporting
- Data easy to obtain from hospital records
(d) / (i) /
- Normal variation in health
- One or two individuals could influence figures
- Average of several measurements reduces effect of error
(ii) /
- Weather
- Other pollutants
- Smoking
- Age
(iii) /
- Dose response relationship strongly suggests cause
- Not possible to eliminate other air pollutant variables in this type of study
- Only one study
- Small sample size at higher concentrations
- Need for causative mechanism to confirm causation
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October 2007
Page 1 ©The Nuffield Foundation, 2007
Copies may be made for UK in schools and colleges
AS Science In Society 1.3 Student Sheets
Vehicle exhausts have become one of the most significant causes of air pollution in Britain. Figure 1 shows average values for carbon monoxide, CO, and oxides of nitrogen, NOx concentrations over a 24 hour period.
Figure 1
(a) (i) Suggest a reason for the shape of the two graphs.
(1 mark)
(ii) Describe the chemical reaction that creates carbon monoxide in a car engine. You can use words, a diagram or a chemical equation.
(2 marks)
(iii) Explain how nitrogen oxides arise in the exhaust, even though petrol does not contain any nitrogen.
(2 marks)
Figure 2
(b) (i) Figure 2 shows average values for ozone concentrations over a 24-hour period.
Explain how, under certain conditions, car exhausts give rise to ozone.
(2 marks)
(ii) Suggest why there is only one peak for ozone concentration during the 24 hours.
(1 mark)
(iii) The equipment widely used for continuous monitoring gives readings with an error of up to 10%. Express the concentration of ozone at 8.00 am showing the range of uncertainty.
Concentration of ozone ...... ± ...... ppb
(2 marks)
Figure 3
(c) A study in London tried to assess the effect of different ozone concentrations on health. Figure 3 shows the relationship between hospital admissions for respiratory diseases and the concentration of ozone.
(i) Describe the relationship shown in Figure 3. You may need to discuss this in two parts.
(3 marks)
(ii) Suggest two reasons why the researchers chose to use hospital admissions as a measure of respiratory disease.
(2 marks)
(d) A scientist commented “a correlation between exposure to air pollution and ill health may reflect chance, bias or cause”.
(i) When very few measurements are made any correlation is more likely to be due to chance than when the measurements are repeated many times. Suggest how chance could explain an increase in hospital admissions if results from only one or two days are included.
(2 marks)
(ii) If the researchers do not consider the effects of other variables they may introduce bias. Suggest three other variables, apart from ozone concentration that might affect hospital admissions for respiratory illness.
(3 marks)
(iii) In this research the researchers made every effort to eliminate chance and bias. Does Figure 3 prove that ozone is a cause of respiratory illness? Explain your answer.
(3 marks)
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Page 1 ©The Nuffield Foundation, 2007
Copies may be made for UK in schools and colleges