Questions

Q1.
 
Carrots are root vegetables that are eaten by many organisms.
An investigation was carried out to study the respiration rate of carrots.
100 g of carrot cubes were placed in a plastic bag containing air. The bag containing the carrot cubes was stored at 1 °C for three days.
All other variables were kept constant.
The percentages of oxygen and carbon dioxide in the bag were measured at the start of the investigation and at the end.
The results are shown in the table below.

(a)  (i)  Suggest two variables, other than temperature, that need to be kept constant in this investigation so that valid results can be collected.
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(ii)  Explain the role of oxygen in the cells of the carrot cubes.
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(b)  Explain how the carrots produce carbon dioxide at the start of this investigation.
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(c)  The investigation was repeated at storage temperatures of 5 °C and 10 °C.
The table below shows the change in percentage of carbon dioxide in the bag at the end of the investigation compared with the start of the investigation for all three storage temperatures.

Explain the effect of temperature on the change in the percentage of carbon dioxide in the bag.
(3)
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(d)  Suggest why the carrot tissue could survive when no oxygen was left in the bag.
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(Total for question = 13 marks)

Q2.
 
Humans and sea anemones have nervous systems with synapses.
The sea anemone, shown in the diagram below, is a marine animal with tentacles.

A student investigated habituation in a sea anemone.
He gently touched a sea anemone, causing it to withdraw its tentacles into its body. He waited and recorded the time for the tentacles to fully re-emerge.
He repeated the process until the sea anemone was fully habituated.
(i)  Suggest what the student would observe when the sea anemone was fully habituated.
(1)
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(ii)  The student investigated the length of time it took sea anemones to lose their habituation.
Suggest how the student carried out this investigation.
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(Total for question = 4 marks)

Q3.
 
A spirometer, filled with oxygen, was used to record the breathing of a student. The student was sitting at rest and was instructed to breathe normally.
The spirometer trace is shown below.

Put a cross  in the box next to the correct description of the changes shown in this spirometer trace.
(1)
   A    the breathing becomes faster and deeper
   B    the breathing becomes slower and deeper
   C    the breathing becomes faster and less deep
   D    the breathing becomes slower and less deep

(Total for question = 1 mark)

Q4.
 
The tissues of some animals can carry out anaerobic and aerobic respiration.
Three investigations were carried out to study respiration in an animal tissue, 
using the apparatus shown below.
The tissue used glucose as the respiratory substrate.
All other variables were kept constant.

The table below shows the three investigations that were carried out and the result 
for investigation 1.

(i)  Complete the table by placing a cross in one box  for each of investigations 
2 and 3 to show the response of the coloured liquid.
(2)
(ii)  Explain why the coloured liquid did not move in investigation 1.
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(iii)  Reduced NAD (NADH + H+) would be formed in investigations 2 and 3.
Describe the fate of reduced NAD in aerobic respiration.
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Q5.
 
The scientific article you have studied is adapted from articles from New Scientist.
Use the information from the article and your own knowledge to answer the following question.
It has been suggested that the fossil record shows there is a relationship between exercise and brain size in humans. It is not certain whether the exercise is causing this effect, or whether it is just a correlation.
Experiments were conducted on mice to help find out more about this.
Discuss how the results of the experiment on mice (paragraph 19) may provide extra information on the relationship between brain size and exercise in humans.
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(Total for question = 3 marks)

Q6.
 
The tissues of some animals can carry out anaerobic and aerobic respiration.
Three investigations were carried out to study respiration in an animal tissue, 
using the apparatus shown below.
The tissue used glucose as the respiratory substrate.
All other variables were kept constant.

The table below shows the three investigations that were carried out.

Explain how investigation 3, shown in the table, could be used to compare the 
rate of respiration of two different tissues.
(2)
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Q7.
 
A spirometer, filled with oxygen, was used to record the breathing of a student. The student was sitting at rest and was instructed to breathe normally.
The spirometer trace is shown below.

Put a cross  in the box next to the mean tidal volume during the first minute of this spirometer trace.
(1)
   A    0.25 dm3
   B    0.45 dm3
   C    4.5 dm3
   D    8.0 dm3

(Total for question = 1 mark)

Q8.
 
A spirometer, filled with oxygen, was used to record the breathing of a student. The student was sitting at rest and was instructed to breathe normally.
The spirometer trace is shown below.

Put a cross  in the box next to the mean breathing rate for the first two minutes of this spirometer trace.
(1)
   A    6 breaths min−1
   B    9 breaths min−1
   C    18 breaths min−1
   D    36 breaths min−1

(Total for question = 1 mark)

Q9.
 
An investigation was carried out to study the effect of positive and negative physical 
and emotional experiences on humans.
The positive physical experience was a warm object placed on the arm of a person for 
five seconds.
The negative physical experience was a hot object placed on the arm of a person for 
five seconds.
All other variables were kept constant.
Two groups of people were used in this investigation. In the first group, the warm 
object was used before the hot object. In the second group, the hot object was used 
before the warm object.
After each experience, the individuals were asked to rate their feelings using the 
scoring system below.

Suggest why one group had the warm object placed on their arm before the hot 
object and the other group had the hot object placed on their arm first.
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Examiner's Report

Q1.
 
(a) (i)
This item required candidates to suggest two variables that needed to be kept constant in an investigation. However, the question stem described aspects of the investigation which meant that some suggestions could not be awarded. Whilst two common incorrect examples are given in the responses below, many candidates offered creditworthy suggestions.
This example shows two suggested variables, neither of which could be credited. However, the reasons are different.

Results Plus: Examiner Comments
The question stem states that 100g of carrot cubes were used and therefore the mass has already been taken into account so cannot be awarded a mark.
The investigation only used one bag and therefore, the moisture content was controlled.

Results Plus: Examiner Tip
Always check the details given to see if a particular variable has already been referred to in the question.

(a) (ii)
This question required candidates to discuss the role of oxygen in respiration. Generally this question delivered a bimodal response. An encouraging number offered detailed and accurate descriptions as per the first example below. A minority, however, offered a rather more general overview as per the second example.
This response delivers a short and accurate answer that gains full marks.

Results Plus: Examiner Comments
The second sentence gained marking point 1 and 2. However it was not sufficiently clear to be awarded marking point 3. The final sentence achieves marking point 4.

This response lacked the precision and detail needed to elicit more than one mark.

Results Plus: Examiner Comments
The first sentence refers to the production of water in the context of oxygen, hence marking point 4 can be given. However, the reminder is inaccurate.

(b)
It was pleasing to see an encouraging number of responses that showed a thorough appreciation of how carbon dioxide is produced within the mitochondrion.
This response shows a sound understanding of the material and gained full marks.

Results Plus: Examiner Comments
The first sentence gives an appropriate introduction that gains marking point 1. The second sentence offers marking point 4, marking point 2 and marking point 5 in the context of the link reaction. It then focusses on the Kreb's cycle.

Results Plus: Examiner Tip
Always check the mark allocation. As this is a 4 mark item, it is likely to demand detail.

(c)
The majority of candidates were able to appropriately comment on the data, noting the positive correlation. However, fewer then offered an explanation of this data as was required.
After an initial description, this response does not tackle the question being asked, so only 1 mark out of 3 can be awarded.

Results Plus: Examiner Comments
The candidate has made a suitable comment on the relationship between temperature change and the change in percentage of carbon dioxide in the bag for marking point 1. However, the candidate has not then elaborated as to why this is the case as required by the command word explain.

Results Plus: Examiner Tip
Always consider the command word. In this case it is 'explain'. Responses, therefore, need to offer reasons for the trends seen in the data rather than just a description of trends.

(d)
Whilst most candidates appreciated that the carrot cells could undergo anaerobic respiration, some incorrectly referred to photosynthesis.
This response illustrates another common misconception for some candidates.

Results Plus: Examiner Comments
Whilst the candidate has correctly referred to anaerobic respiration, the latter part of the sentence describes such respiration in animal cells rather than plant cells so the mark cannot be awarded.

Results Plus: Examiner Tip
Make sure that all of your answer is correct.

 

Q2.
 
(i)
Many candidates displayed their understanding of habituation in the context of the sea anemone, as illustrated in the example provided.
This candidate has offered both required elements and so gains the mark.

Results Plus: Examiner Comments
This answer refers to both the stimulus and the response so can be awarded the mark.

(ii)
Some candidates tackled this question item well, giving good detail. However, others found it challenging and the full mark range was seen.
This example illustrates a clear and logical answer that gains full marks.

Results Plus: Examiner Comments
The initial sentence gives a description of habituating sea anemones but in the context of the answer it can be assumed that the sea anemones subsequently being referred to are those that have been habituated so marking point 1 can be awarded.
The next two sentences appropriately describe leaving sea anemones for differing lengths of time before stimulating them for marking point 2.
The next sentence then describes recording the time at which the habituation is lost.
Neither the reference to ten sea anemones in the opening sentence, nor the final sentence give sufficient detail for marking point 3.

This response was fairly representative of a sizeable minority of candidates. It tended to describe the habituation process for the sea anemone rather than tackling the question which focussed on how to judge the time when a habituated sea anemone had lost its habituation.

Results Plus: Examiner Comments
There were no awardable marks seen in this answer.

 

Q3.
No Examiner's Report available for this question

Q4.
 
(ii)
This item required candidates to explain why the coloured liquid in the respirometer did not move for the conditions described in the table. Most candidates were able to achieve one mark but only about one-fifth gained all 3 marks.
This answer gained 2 marks and illustrates the most common reason for not gaining full marks.

Results Plus: Examiner Comments
This candidate begins their answer with mp 3 and then suitably offers mp 1.
The candidate has also recognised that the animal tissue respiring anaerobically would produce lactate but has not made reference to the fact that no carbon dioxide would be released.
2 marks

This answer also gains 2 marks and illustrates another common way that candidates did not gain full marks.

Results Plus: Examiner Comments
This candidate has recognised the substrate and product of anaerobic respiration in animal tissue but has not then linked this with no change in volume or pressure changes in the respirometer.
Mp 1 and mp 2 awarded.

(iii)
Many candidates were able to present detailed and accomplished responses to this item. They were required to describe the fate of reduced NAD in aerobic respiration.
This candidate has provided a complete answer that shows clear understanding of the material and has achieved the maximum of 4 marks.

Results Plus: Examiner Comments
An answer that starts with the movement of the reduced NAD (mp 2) and its change to the oxidized form (mp 3) as it 'hands over' electrons to the electron transport chain (mp 4) and protons that are forced through into the intermembranal space (mp 5).
The final comment describes how the NAD is available again for the Kreb's cycle (mp 6).
Max = 4 marks

Results Plus: Examiner Tip
Make sure that the response has sufficient points to match the mark allocation.

 

Q5.
No Examiner's Report available for this question

Q6.
 
Whilst there was a number of pleasing answers to this How Science Works question, many candidate responses would have benefitted from more detail.
This response achieves both marks but also illustrates a number of other salient points.

Results Plus: Examiner Comments
The candidate starts their response with a suggestion of keeping the temperature constant. However, this is not credit-worthy because it was stated that all variables were kept constant.
Subsequently, an appropriate reference to mp 1 is given. Of the two mark points, this was the point less commonly-encountered.
Towards the end of the passage, the candidate makes correct reference to distance and time, to gain mp 2. Frequently, candidates did not include a time reference for mp 2.
2 marks

Results Plus: Examiner Tip
Check the description of the investigation carefully, to make sure of the detail - such as which variables are already being controlled.

 

Q7.
No Examiner's Report available for this question

Q8.
No Examiner's Report available for this question

Q9.
 
This question item required candidates to think about experimental design and How Science Works in the context of considering the sequence of how a procedure is performed.
This example shows one way that candidates tend to express mp 1.

Results Plus: Examiner Comments
This response achieved mp 1 only.
1 mark

 

Mark Scheme

Q1.

 

Q2.

 

Q3.

 

Q4.

 

Q5.

 

Q6.

 

Q7.

 

Q8.

 

Q9.