Topic 3 Longer Response Exam Questions

Q1.
 
Sperm are produced from stem cells in a process that involves several cycles of mitosis and a single cycle of meiosis, as shown in the diagram.

(i)  State what is meant by the term stem cell.
(2)
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(ii)  Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells.
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(Total for question = 6 marks)

Q2.
 
Insulin is a protein produced by beta cells in the pancreas. Insulin is synthesised on 
ribosomes, then modified and packaged in vesicles. It is stored in these vesicles until 
it is secreted.
The diagram below shows the organelles involved in this process of modifying and 
packaging the insulin in vesicles.

* Using the information in the diagram, describe how insulin is modified, packaged 
and secreted by the cell.
(4)
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Q3.
 
Type 1 diabetes occurs when beta cells in the pancreas do not produce insulin.
Stem cells produced from skin cells can be used to replace these beta cells in mice. The skin cells can be stimulated to become pluripotent stem cells.
The pluripotent stem cells were injected into the mice. After eight weeks, these cells had developed into insulin-secreting beta cells.
Describe how these pluripotent stem cells became specialised beta cells.
(4)
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Q4.
 
Obesity can be affected by both genetic and environmental factors. An indicator of obesity is the body mass index (BMI).
The effects of a gene called FTO, saturated fats and physical exercise on BMI were investigated.
There are two alleles (FTOT and FTOC) at the FTO locus.
The effects of saturated fats in the diet on the BMI in individuals with different FTO genotypes are shown in the graph.

Deduce the effect of environmental and genetic factors on BMI.
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(Total for question = 3 marks)

Q5.
 
The diagram shows some of the cell organelles involved in the formation of extracellular enzymes.

Describe the roles of parts B and C in the formation and transport of extracellular enzymes.
(4)
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(Total for question = 4 marks)

Q6.
 
Obesity can be affected by both genetic and environmental factors. An indicator of obesity is the body mass index (BMI).
The effects of a gene called FTO, saturated fats and physical exercise on BMI were investigated.
There are two alleles (FTOT and FTOC) at the FTO locus.
(i)  Which of the following describes what is meant by the term locus?
(1)
   A    genetic code for a protein
   B    holds together sister chromatids
   C    location of a gene on a chromosome
   D    paternal part of a genome

(ii)  Compare and contrast the structures of a saturated fatty acid and an unsaturated fatty acid.
(3)
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(Total for question = 4 marks)

Examiner's Report

Q1.
 
(i)
Most candidates had a good idea of what a stem cell is and provided good statements that gained both marks.

Results Plus: Examiner Comments
A concise answer that gains both marks.

Results Plus: Examiner Tip
As you learn your Biology make sure you understand and can use relevant biological terms.

Results Plus: Examiner Comments
This response did not gain any marks; 'the ability to turn into any other cell' was not sufficient for MP2.

Results Plus: Examiner Tip
Think carefully about the way you express scientific ideas. It is very easy to write an answer that lacks sufficient clarity to gain marks.

(ii)
Candidates were asked to compare and contrast the results of meiosis and mitosis. Candidates generally gained marking point 2 recalling that mitosis produces diploid cells and meiosis produces haploid cells.
Although few candidates described the overall contribution of mitosis and meiosis to sperm cell numbers (MP4) a number gained the allowed alternative answer gaining MP4 for a correct description of the number of daughter cells.
Many candidates described mitosis as producing 'identical daughter cells' and 'meiosis producing non-identical daughter cells'; this was not sufficient for marking point 3. To gain MP3 it had to be clear that candidates were talking about genetically identical and genetically non-identical daughter cells.
Very few commented on the idea that both mitosis and meiosis increase the number of cells for MP1.

Results Plus: Examiner Comments
This response gained all four marks, although each mark point had to be pieced together.

Results Plus: Examiner Tip
When asked to compare and contrast try to include each comparison or contrast in the same sentence e.g. mitosis produces diploid cells whereas meiosis results in haploid cells'. 
Alternatively, consider using a table format.

Results Plus: Examiner Comments
For this response the candidate gained one mark, MP2. 

A full comparison was not made for MP3 and 4, and it was not clear that meiosis results in an increase in the number of cells, so MP1 could not be awarded.

 

Q2.
 
This question was generally answered very well with most candidates scoring well. As a question focusing on QWC (Quality of Written Communication), marks were awarded for statements in a logical sequence, demonstrating an understanding of the processes involved as a protein is transported through the cell from the rER to the cell surface membrane.
The diagram proved to be very useful memory aid! However, not all candidates realised that the rER puts the insulin into vesicles, indeed many appeared to think that the protein becomes a vesicle at the end of the rER. There was also some confusion between the roles of the rER and the Golgi apparatus. Although there may be some modification of the protein within the rER, candidates are expected to know that the protein is folded into its secondary and tertiary structure in the rER, with further modification happening within the Golgi apparatus.
Those responses that did not score well were those where there was confusion between ribosomes, vesicles and proteins - with references to ribosomes moving through the rER and vesicles being modified in the Golgi apparatus.

Results Plus: Examiner Comments
This response gained no marks, despite referring to the transport of insulin in vesicles. This is because the context was incorrect - describing the movement of the insulin from the smooth ER to the rER and then out of the cell. The structures in the diagram had not been correctly identified and the process was not described accurately.

Results Plus: Examiner Comments
This response gained full marks for insulin being folded into tertiary structure in the rER, packaged into a vesicle, the vesicle fusing with the Golgi apparatus, modification of the insulin in the Golgi (generously allowed).
(The mark for exocytosis would not have been allowed for description of lysosomes instead of vesicles transporting 'it' from the Golgi.)

Results Plus: Examiner Tip
Avoid referring to 'it' - although you know what 'it' refers to, this may not be clear to the examiner. In this response, the sentence 'The vesicle then fuses with the Golgi apparatus' is followed by one that starts 'It is then modified in the Golgi' - the 'it' could be interpreted as being the vesicle rather than the insulin and would not be given the mark. Better to make it perfectly clear, i.e. 'The insulin is then modified…'.

 

Q3.
 
(ii) Many candidates were able to recall the process of differential gene expression and outlined it succinctly, gaining full points. Sadly, others floundered as if they were unfamiliar with the topic or had failed to grasp how to apply their knowledge to the question. Clarity of expression let many candidates down, such as referring to the mRNA transcribing the gene, rather than mRNA being produced by the process of transcription. Other common misconceptions were that RNA transcribes DNA, mRNA is 'transcripted', active 'cells' are transcribed and that active genes are 'read by' mRNA.
Responses that mentioned transcription factors and promoters tended to be unclear - these were probably written by candidates re-sitting this paper, having studied the topic in further depth in Topic 7; although this depth of knowledge is not required at AS, credit would have been given if the answer was clear.

Results Plus: Examiner Comments
This response gained full marks for correctly referring to a chemical stimulus, the switching on of genes, mRNA produced by transcription from the active gene and the protein produced permanently determining the function of the cell.
Note - no mark could be given for stating that 'mRNA is made into protein during translation' - better to state that translation of the mRNA results in the production of a protein.

Results Plus: Examiner Comments
This response gained 1 mark for reference to a chemical stimulus. The common error of referring to 'cells' instead of 'genes' being switched on lost a mark. Then the muddled sentence concerning 'those who are switched on got transcribed at mRNA', was not creditworthy.
If this response had been better worded and more accurate, it could have gained 3 marks instead of 1.

Results Plus: Examiner Tip
Take care with terminology - genes are switched on or activated, not cells, and genes are transcribed to produce mRNA.

 

Q4.
 
This question asks candidates to analyse data about diet and genotype, the link between genetic effects and environmental effects. The command word "deduce" requires them to draw conclusions.
Most candidates gained 1 mark for recognising the link between a saturated fat diet and BMI. Many candidates then recognised that there was some link between genotype and BMI, but didn't gain a mark because they failed to say that it was only the homozygous that had an effect. Very few candidates stated that the allele was recessive.

Results Plus: Examiner Comments
This answer shows good analysis of the data, stating that BMI is affected by a saturated fat diet but the effect is greater if the individual has the homozygous genotype. However, there is no recognition that this shows the allele is recessive, so gains 2/3 marks.

Results Plus: Examiner Comments
Again, this response gains 2/3 marks for analysing the data but not making the link between the data and a recessive allele.

Results Plus: Examiner Tip
Many candidates are quoting the data or carrying out some manipulation but no marks are awarded for this in the new specification unless specifically asked for.

 

Q5.
 
This question scored quite well with a large percentage of candidates gaining 3 or 4 marks.
The process of enzyme production was well understood although some candidates' responses lacked the detail needed to link structure to function.
Referring to B and C was acceptable as long as the context was correct.

Results Plus: Examiner Comments
The mention of exocytosis may have been a mark on previous exam papers. It is clear in this response that the concept is not fully understood. They have, however, got as far as fusing with the cell membrane and have gained that mark.

Results Plus: Examiner Tip
In questions with a sequence or pathway, consider the stages immediately before and after to complete the story.

 

Q6.
 
(ii)
This question was a comparison question between saturated and unsaturated fatty acids. More marks were gained for the differences than the similarities. Many candidates lost the mark for the double bond because they didn't state it was between carbon atoms, although there were also some good descriptions of the C-C and C=C bonds. Quite a number confused fatty acids with triglycerides in their answer.

Results Plus: Examiner Comments
This answer describes the differences clearly, gaining 2 marks, but there are no similarities given. 2/3

Results Plus: Examiner Tip
Always read the command words carefully. If the question is compare and contrast, it is not possible to gain full marks without at least one similarity and one difference.

Results Plus: Examiner Comments
Again, a clear description of the differences but no similarities. 

The 2 marks can be awarded here because the differences are clearly stated even though they are both put together in one sentence.

 

Mark Scheme

Q1.

 

Q2.

Q3.

Q4.

 

Q5.

 

Q6.