My Question Paper. Maximum Mark. Mark Awarded. Question. Total Mark. Page 1 of 27 WJEC/CBAC 2016 pdfcrowd.com

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1 My Question Paper Question Maximum Mark Mark Awarded Total Mark Page 1 of 27 WJEC/CBAC 2016

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4 3. The diagram below shows a component of DNA. Name the parts A, B and C. [3] A B C (b) Describe how a polymer of DNA would be different from a polymer of RNA. [2] Page 4 of 27 WJEC/CBAC 2016

5 (c) (i) Name the stage in the cell cycle where DNA replication occurs. [1] (i) (ii) Vincristine is a drug which prevents the spindle fibres from shortening. Name the stage in the cell cycle which would be affected. [1] (iii) State three differences between daughter cells produced by the process of mitosis and those produced by meiosis. [3] Page 5 of 27 WJEC/CBAC 2016

6 4. (a) The diagram below shows a unit which makes up nucleic acids. (i) Name the structural unit shown. [1] (ii) Name component A. [1] (iii) Name component B in DNA and RNA. [1] DNA RNA (iv) Name the four components found in DNA, represented by C. [2] Page 6 of 27 WJEC/CBAC 2016

7 (b) Describe how the structural units, drawn in part (a), are arranged in DNA molecules. [4] (c) Describe the function of DNA molecules in cells. [1] Page 7 of 27 WJEC/CBAC 2016

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11 7. The diagram below shows a simple nucleotide. (a) On the diagram above, draw a circle around the component that contains nitrogen. [1] (b) Describe two differences between a DNA nucleotide and an RNA nucleotide. [2] An experiment was carried out to determine the relative percentages of the bases in DNA from various organisms. The results are shown in the table below. Page 11 of 27 WJEC/CBAC 2016

12 (c) DNA is a double stranded molecule. Explain how the data in the table supports the concept of complementary base pairing. [2] Page 12 of 27 WJEC/CBAC 2016

13 8. The diagram below illustrates replication of DNA in cells. (a) (i) Describe the sequence of events shown within the dotted rectangle in the diagram above. [3] (ii) What is the role of DNA polymerase in the process? [1] (b) Explain why the process is referred to as 'semi conservative'. [2] Page 13 of 27 WJEC/CBAC 2016

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15 9. Answer one of the following questions. Any diagrams included in your answers must be fully annotated. Either, (a) Describe how a nucleotide sequence on a DNA molecule results in the production of a polypeptide. Or (b) Describe the principles and techniques involved in the cloning of plants. Give the advantages and disadvantages of this process. [10] Page 15 of 27 WJEC/CBAC 2016

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17 Marking Scheme 1. Page 17 of 27 WJEC/CBAC 2016

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20 4. (a) (i) Nucleotide; 1 (ii) Phosphate / phosphoric acid / PO4 / PO3-; NOT phosphorus / P; 1 (iii) Deoxyribose in DNA and ribose in RNA (both); 1 (iv) Adenine, Thymine, Cytosine, Guanine (1 if 1 error). 2 (b) Any 4 Pairing described A-T and C-G (both needed); Backbone / Chains / polynucleotide formed by alternating sugar phosphate groups; two chains connected / joined by base pairs; hydrogen bonding; two chains (twisted) to form a helix / double helix; NOT alpha helix. 4 Accept labelled diagram. (c) {forming template / code / instructions} for {protein synthesis / mrna / amino acid sequence / primary structure of protein / transcription} (accept Replication in dividing cells) / NOT genetic material alone. 1 Question total 10 Page 20 of 27 WJEC/CBAC 2016

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24 Examiner's Comments 1. (a) There was some confusion between a DNA molecule and a DNA strand, but the majority of candidates responded well to this question. (b) (i) Good, but some incorrect responses such as, bases, nucleotides and amino acids were given. (ii) This question required some thought but we were pleased by the number of candidates who were able to give two correct controlled variables. (c) (i) Usually well argued, but the weaker candidates found it difficult to explain in exact terms. Few candidates explained what banding pattern would be expected if there was conservative replication. (ii) Only the A grade candidates were able to get the correct distribution and the correct proportions. This comment originally referred to question 5 on paper 1075/01 (22/06/2011) 2. The majority of candidates scored highly on this question. This comment originally referred to question 5 on paper 1071/01 (11/01/2012) 3. This was answered to a high standard by most candidates, especially part (c). In part (a) it was disappointing to see some candidates naming part B as a pentose sugar rather than deoxyribose as the molecule was clearly identified as DNA in the question. In part (b) it is worth stressing to candidates that whilst we do accept phonetic spellings, care must be exercised when a spelling could be confused with another word, for example thyamine could be confused with thiamine which is vitamin B1 not a nitrogenous base. In part (c)(iii) some candidates made references to the number of divisions. This was not accepted as the question was asking for differences between the cells produced not the processes. Some also made reference to the cells containing half the number of chromosones or 23 vs 46 without referring to the parent cell. This was not accepted in place of haploid/diploid. This comment originally referred to question 4 on paper 1071/01 (21/05/2014) Page 24 of 27 WJEC/CBAC 2016

25 4. This question was also well answered by most candidates. Part (a) (i) has been asked many times before but some candidates still gave incorrect responses including 'nucleic acid' and even 'DNA'. Correct spellings were required for part (iv); candidates should be advised that they must be able to spell the names of the bases. In part (b) poor quality of written communication hindered some candidates; also some candidates confuse the double helix with the alpha helix. In part (c) candidates are required to describe the function i.e. make the link between base sequence and amino acid sequence some gave a vague answer like 'contains genetic information' which is not a description. This comment originally referred to question 3 on paper 1071/01 (14/05/2012) 5. Question (b) was the more popular and on the whole, better answered of the two questions in this section. The commonest mistake in the answers to part (a)(i) was for candidates to give a detailed description of mitosis which not only wasted their time but also scored no marks. The usual points made in this part were a reference to growth and the fact that mitosis gives rise to identical/genetically identical cells. Few candidates gave any relevant examples despite the question asking for examples. The other marking points in part (a)(i) were seen only rarely. Part(a)(ii) was usually more mark yielding with all marking points being seen though candidates usually made reference to haploid vs. diploid, two divisions vs. one and crossing over leading to variation in meiosis. A common mistake in (b) was for candidates not to make it clear that it is a nucleotide that has three components instead, many referred to the DNA molecule or, more usually DNA having three components. Few candidates made reference to purines and pyrimidines which meant several marking points were not accessible and very few candidates made any reference to the sequence of bases determining the amino acid sequence of a protein. A reminder that diagrams should be fully annotated otherwise they will gain no credit. Few candidates made any reference to the sugar phosphate backbone and surprisingly a sizeable number made no reference to complementary base pairing. This comment originally referred to question 8 on paper 1071/01 (16/05/2011) Page 25 of 27 WJEC/CBAC 2016

26 6. (a) (i) Transcription and translation were often the wrong way around and several candidates incorrectly gave translocation for translation. (ii) Most candidates achieved 6 marks or more for this question, but 8 was rare. (b) It was very rate to see a correct answer here, the sequence of nucleotides on the mrna being given. This comment originally referred to question 6 on paper 1075/01 (22/06/2011) 7. This question was generally well answered by the majority of candidates. However a large number of candidates referred to the structure of nucleic acids and not the nucleotides within DNA and RNA. Few students gained both marks in part (c) as they failed to quote data from the table. This comment originally referred to question 1 on paper 1071/01 (08/01/2014) 8. Most candidates described the unzipping of the double helix in some way and the free nucleotides aligning due to complimentary base pairs. The most common omission was the unwinding of the helix. Some candidates made rather vague reference to the enzyme helicase and there was a good deal of confusion about the role of polymerase which was described in this part as well as in part(ii). A small number of candidates described the process as transcription and referred to RNA nucleotides. In part(ii) candidates should know that the primary function of polymerase, as its name implies, is making a polymer by joining nucleotides together. There was some confusion over bases and nucleotides and many candidates used the term bases when they clearly meant nucleotides. There were some inaccurate explanations in part (b), indiscriminate use of the terms strand, old and new resulted in some confusing answers. The best answers referred to molecules of DNA, and were clear about their descriptions of the origins of each of the strands in the double helix. This comment originally referred to question 2 on paper 1075/01 (20/06/2014) 9. (a) Responses to the essay on how a nucleotide sequence on a DNA molecule results in the production of a polypeptide were excellent with many candidates getting all points on the mark scheme. (b) The essay describing the principles and techniques involved in the cloning of plants together Page 26 of 27 WJEC/CBAC 2016

27 with the advantages and disadvantages of this process was not quite as popular as the essay on protein synthesis but was equally as well answered. This comment originally referred to question 7 on paper 1075/01 (17/06/2013) Page 27 of 27 WJEC/CBAC 2016