Topic 3 Data Analysis Exam Questions

Q1.
 
Tuberculosis (TB) is an infectious disease caused by mycobacteria.
Individuals infected with M. tuberculosis can be treated with antibiotics.
Four of the antibiotics used to treat TB are shown in the table.

In one clinical trial lasting six months, the effect of treating TB with these antibiotics was investigated.
All patients were treated with all four antibiotics for two months. Then they were treated with different pairs of antibiotics or isoniazid alone for a further four months.
All patients were free of any signs of active TB at the end of the clinical trial.
The design of the trial and the percentage of these patients with TB three years after the trial ended are shown in the diagram.

Analyse the data to comment on the effectiveness of these antibiotics for the treatment of TB.
(6)
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(Total for question = 6 marks)

Q2.
 
Cigarette smoking is associated with several medical problems.
In an investigation, some female mice were exposed to cigarette smoke during pregnancy.
The ability of their male offspring to produce sperm and the activity of the sperm were investigated.
The results of this investigation are shown in the table.

Analyse the data to explain why exposing pregnant mice to cigarette smoke affects the fertility of their male offspring.
(3)
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(Total for question = 3 marks)

Q3.
 
The relationship between the length of a sperm cell and the speed at which it can swim was investigated.
The data collected are shown in the graph.

(i)   Calculate the swimming speed of a sperm cell that is 40 μm long, as predicted by the line shown on the graph.
(2)

 Answer ........................................................... 
(ii)  Explain the limitations of using the line on the graph to predict the swimming speed of sperm cells.
(2)
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(Total for question = 4 marks)

Q4.
 
Fibrosis of the liver is a chronic condition that can lead to cirrhosis of the liver and liver failure.
In fibrosis of the liver, liver cells secrete excess collagen.
There is an association between fibrosis of the liver and alcohol consumption in humans.
Scientists have investigated the effects of alcohol intake on collagen synthesis in rats.
The results are shown in the table.

(i)  Deduce the effect of alcohol intake on fibrosis of the liver in rats.
(3)
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(ii)  The scientists have suggested that epigenetic events are involved in regulating collagen synthesis in rats given alcohol.
Explain how epigenetic events might be involved in regulating collagen synthesis in rats given alcohol.
(2)
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Q5.
 
Tissues of the human body have different stem cell populations.
These stem cells divide to replace and renew cells in these tissues.
Scientists have observed a relationship between the number of times a stem cell population divides in a tissue and the risk of developing cancer in that tissue.
This relationship is shown in the graph.

(i)  The correlation coefficient for the data is 0.937.
The table shows some critical values for this correlation coefficient.

Which of the following correctly describes the correlation?
(1)
   A    non-significant and positive
   B    non-significant and negative
   C    significant and positive
   D    significant and negative

(ii)  Explain the relationship between the number of stem cell divisions and the risk of developing cancer.
(2)
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(iii)  The graph shows that the risk of developing lung cancer is greater in a cigarette smoker compared to a non-smoker.
Calculate how many times greater.
(2)

Answer ...........................................................
(iv)  Explain why cigarette smokers have a higher risk of developing lung cancer than non-smokers.
(2)
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Examiner's Report

Q1.
 
This was a six-mark levels based question. Examiners read the response and decide on the level of response, they then decide if the response is at the upper mark for that level or the lower mark.
The mark scheme provides guidance on relevant content and on how this might be used to determine a particular level of response.
For this question candidates were provided with information about a clinical trial using different combinations of antibiotics to treat TB patients. They were provided with information on the mode of action of the antibiotics.
Responses that contained only a description of the antibiotic trial results, were considered to be at level 1. Responses that attempted to explain the reasons for differences in the results, were considered to be at level 2, e.g. suggesting that antibiotics with different modes of action or targets work better as combinations. If candidates tried to use information about the mode of antibiotic action with their own understanding e.g. bring in ideas such as dormancy of TB, bacteriostatic and bactericidal antibiotics, if they comment on trial design e.g. missing combinations of antibiotics, then the response is probably at level 3.

Results Plus: Examiner Comments
This response considers in detail all the information provided. The candidate has used information about the results of the trial, about the antibiotics required for a good level 2 response. 
The candidate has also brought in their own biological knowledge and has commented on the design of the trial, extending the quality of response to level 3.

Results Plus: Examiner Tip
Remember to use all the information provided as well as your own biological knowledge and understanding.

 

Q2.
 
In this question candidates were asked to analyse data to explain why exposure to cigarette smoke affects fertility. The phrase 'Analyse the data' is used to direct students to information they should use to help them answer the question.
Many candidates simply described the data and did not include an element of explanation. Better responses were produced when candidates looked at each bit of information and tried to explain why it would reduce fertility.

Results Plus: Examiner Comments
This candidate produced a well organised answer that gains three marks, for MP2, MP1 and MP3.

Results Plus: Examiner Tip
When asked to explain some results, first decide what the information tells you. Then write your answer providing an explanation for each key bit of information.

 

Q3.
 
(i)
This question assessed candidates' ability to work with linear relationships of the form y = mx + c (mathematical skill A.3.3). Many candidates answered successfully by finding the gradient of the line on the graph, which allowed them to extrapolate beyond the extent of the x-axis. However, some candidates extended the x-axis and the line on the graph and attempted to read the swimming speed directly from their extended graph. Although this was a creative approach, it usually did not yield a sufficiently accurate answer. A disappointing number of candidates failed to achieve the second mark for use of correct units, even though these really could be taken directly from the graph. Some candidates omitted units entirely, while another surprisingly common mistake was for the 's' to become superscript which is biologically nonsensical.

Results Plus: Examiner Comments
The working (beside the graph) in this answer reflects a valid method of extrapolation. Unfortunately the candidate has not read the graph accurately enough so has not obtained the correct answer, and units are omitted, so neither of the two marks could be awarded.

Results Plus: Examiner Tip
You are expected to read graphs as accurately as possible, even if the reading is in-between the grid lines. For example, at a length of 20μm the line is half-way between the grid lines for 62 and 64μm s-1, so you should read off 63μm s-1.

(ii)
Of course, linear extrapolation is not always appropriate in biological contexts. This question asked candidates to consider the limitations of the swimming speed they had predicted in part (i). Answers tended to focus on either the first or the second bullet point in the mark scheme, rarely considering both. Bullet point 1 was much more frequently seen by the examiners, probably because the variability of the data visible in the graph helped to point candidates in the right direction.

Results Plus: Examiner Comments
This answer correctly explains the first bullet point in the mark scheme, so was awarded 1 mark.

Results Plus: Examiner Tip
Look for signposts as to how many points to include in your answer. In this case the question refers to limitations (plural), and two marks were available, so the examiners were looking for two distinct points.

Results Plus: Examiner Comments
This answer correctly explains the second bullet point in the mark scheme, so was awarded 1 mark.

 

Q4.
No Examiner's Report available for this question

Q5.
No Examiner's Report available for this question

Mark Scheme

Q1.

 

Q2.

 

Q3.

 

Q4.

 

Q5.