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Topic 5 Extended Response Questions	

 	
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Questions

Q1.
 
It has been estimated that only 5% of the light energy hitting the surface of a leaf reaches the chloroplasts to be used in the synthesis of organic material. The total energy used in this synthesis is known as the gross primary productivity (GPP).
(a) Suggest two reasons why 95% of the light hitting the surface of a leaf is not used by the chloroplasts.
(2)
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(b) The mean GPP for plants on Earth is 24.4 × 106 J m−2 year−1.
The plants use 3.7 × 106 J m−2 year−1 of this energy in metabolic processes. The energy in the remaining organic material is known as net primary productivity (NPP).
(i) Explain what is meant by the unit J m−2 year−1.
(1)
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(ii) Calculate the percentage of the mean GPP that remains as NPP within plants on Earth.
 Show your working.
(2)

Answer ...............................................................................................................%
(iii) Place a cross  in the box next to the metabolic process that best describes the process that accounts for most of the difference between GPP and NPP in plants.
(1)
  A   Chemosynthesis
  B   Respiration
  C   Photosynthesis
  D   Protein synthesis
*(c) With reference to the structures in a chloroplast, explain how the energy from light is made available in ATP molecules for the synthesis of organic materials.
(6)
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(Total for question = 12 marks)

Q2.
 
Nuthatches are small, colourful birds belonging to the genus, Sitta.
 Many varieties of the species Sitta europaea (European nuthatch) can be found throughout mainland Europe.
These varieties form overlapping populations in different regions. These birds eat small invertebrates, living in tree bark, throughout the year.

However, in the colder mountain forests on the island of Corsica, a small population of approximately 2500 pairs of nuthatches can be found. These birds are classified as the species Sitta whiteheadi (Corsican nuthatch). For most of the year, they feed on pine seeds. During the summer breeding season they also feed on small invertebrates.
Members of the two species, S. europaea and S. whiteheadi, are so similar in appearance and behaviour that they can usually only be distinguished by expert observation and research.
(a) Place a cross  in the box next to the best definition of a species.
(1)
  A  individuals can interbreed to produce fertile offspring
  B  individuals can interbreed to produce hyrbid offspring
  C  individuals can interbreed to produce sterile offspring
  D  individuals can interbreed to produce viable offspring

*(b) In mountainous regions of mainland Europe, only S. europaea is found. Suggest how a distinct species of nuthatch, S. whiteheadi, has evolved in the mountainous regions of the island of Corsica.
(5)
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(c) (i) Suggest how environmental changes, such as those caused by global warming, are more likely to cause extinction of S. whiteheadi than S.europaea.
(3)
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(ii) Suggest why S. whiteheadi might be able to survive an environmental change such as global warming.
(2)
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(d) Explain how the work of zoos could be important to the survival of S. whiteheadi.
(2)
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(Total for question = 13 marks)

Examiner's Report

Q1.
 
(a) Most candidates were able to suggest two acceptable reasons.

Results Plus: Examiner Comments
The response has correctly identified the need for the correct wavelength. The reference to deflection would not quite be creditworthy. However, transmission through the leaf can be awarded.

(b) (i) It was expected that at this level candidates would be able to expand the unit symbols fully. Many candidates either did not refer to the 'square metre' or gave 'metre' with a superscripted 2. A noticeable number of candidates gave incorrect interpretations of 'm' e.g. molecule or minutes.

Results Plus: Examiner Comments
The candidate has not expanded the square metre fully.

Results Plus: Examiner Comments
Here the reference to each unit is explained. Area was acceptable instead of square metre.

(b) (ii) Most candidates were able to complete some of the calculation. Of these, a small majority were able to complete it fully to give the final percentage.
(c) On this question, it was pleasing to see a large number of high-scoring answers. Candidates showed good understanding of the process and were able to give straightforward, accurate accounts. It is pleasing that so many candidates can tackle the details of biochemical processes at this level. It was noticeable that many candidates included details of the light-independent stages. The question required that an account would be given up to the point at which the energy was available in ATP rather than how it was used. The spelling of the required technical terms did not need penalising on many occasions.

Results Plus: Examiner Comments
This is a mid-level answer. Mps 1, 2, 3 and 5 can be awarded. The references to phosphorylation do not explain what is being used. There is some repetition towards the end.

Results Plus: Examiner Tip
When explaining a synthesis, give the full process from starting point e.g. ADP + inorganic phosphate, to product e.g. ATP.

Q2.
 
(b) The multiple choice question caused few problems, with the majority of candidates selecting the correct answer.
Candidates generally wrote extensive answers for part (b), demonstrating an understanding of the process of speciation. It was evident that candidates had also used past mark schemes. Disappointingly, the average mark for this item was only 3 out of 5; primarily a result of poor Biological expression. Some candidates lost a mark through incorrect spelling; this item was our QWC question testing spelling of Biological terms.
This example illustrates a high-scoring answer, but also some of the poor wording that we saw.

Results Plus: Examiner Comments
This was awarded mp 1 and 2, but could not be awarded mp 4 as the selection pressures do not cause mutations; a mistake frequently seen. Better adapted alleles is not acceptable for mp 5 but we reluctantly accepted useful alleles for mp 6. Mp 4 was given further down, where the context was more appropriate, but mp 5 still could not be awarded as we wanted some idea of what the adaption was to.

Results Plus: Examiner Tip
At A2 we are stricter about the phraseology of your answers. When you have finished revising a topic, either read about it in a textbook or look at past mark schemes more carefully, paying attention to the actual wording. Keep your sentences very short as well.

Results Plus: Examiner Comments
This was a typical answer. The candidate fell into the trap of referring to the nuthatches being separated by the mountains. They did get awarded mp 2, 4 and 5.

Results Plus: Examiner Tip
It is difficult under the pressure of exam conditions, but always read the question and your answer through very carefully to ensure that your answer is in the context of the question. A2 questions require a context-based answer, by their very nature.

(c) This question did cause problems, with very few candidates scoring all three marks.

Results Plus: Examiner Comments
This response has been included in this report to demonstrate the clarity of candidate's answers that are short, straightforward responses.

Results Plus: Examiner Tip
Although you will not get any marks for simply writing keywords down, you can write very short, simple sentences underneath each other. Not only will this make your answers easier to mark (more of an advantage to us!) but it will help you express yourself more clearly and help you to write enough relevant points to get full marks for the question. Always aim to write one or two more points than there are marks available.

(d) Candidates clearly know a lot about the role of zoos in the conservation of organisms and some very detailed accounts were given. However, candidates only scored one mark on average for reference to the breeding programmes. Many talked about their role in education which was not really relevant to the context of this question.
This was a very typical response. It only scored mp 1.

Results Plus: Examiner Comments
Simply putting the birds back into the wild would not be sufficient; they need to be returned to habitats appropriate to their survival.

Results Plus: Examiner Tip
When you think you know the answer to a question, particularly if it is one that you have seen on a past paper, check that you have tailored your response to fit the context of the question. You need to be quite specific in your answers at A2.

Mark Scheme

Q1.

Q2.