2021 EJC Promo JC1 P2 Bio (A)

©EJC 2021 9744/J1H2/Promo/2021 [Turn over EUNOIA JUNIOR COLLEGE JC1 Promotional Examinations 2021 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME ANSWER KEY (with Examiners’ Comments) CIVICS GROUP 2 1 - REGISTRATION NUMBER H2 Biology Paper 2 Structured & Free Response Questions 9744 05 October 2021 2 hours Additional Materials: 12-page Answer Booklet. READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer all questions in the 12-page Answer Booklet. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 8 2 8 3 8 4 8 5 10 6 10 7 8 Section B 8 20 Total 80

2 9744/J1H2/Promo/2021 READ THIS FIRST! 1. The biology teachers have spent time writing the examiners’ comments in this answer key, as well as the individual comments on your scripts. Do take time to read through them carefully, and note the common mistakes, misconceptions and phrases to avoid. This is an important part of learning. 2. As you read the answer key, note about any questions that you may have, and clarify them with your respective tutor as soon as possible. 3. It is not about matching words in your answer to the mark scheme. Your answer should be conceptually sound; having all the words doesn’t necessarily make your answer correct. E.g. enhancer is a gene, it codes for activators which binds to enhancers to increase rate of reaction by promoting formation of transcription initiation complex. The above statement “hits all the right words” but it is conceptually wrong, so no mark will be awarded. 4. Different questions have different requirements. You will need to apply your conceptual understanding and keywords based on the context of the question. It is not one size fits all. 5. You should never have the mindset that content / concepts tested will not come out again. You are preparing for the A-Level Examinations, all learning leading up to it should be retained (and not forgotten). 6. As part of learning, you should analyse your papers and find out what are your gaps: i. Content ii. Concepts iii. Q uestion analysis skills iv. Answering techniques and writing skills 7. It is important to reflect on this learning experience, consolidate your learning and build on your learning resources (notes, tutorials, worksheets, tests, etc.) to better prepare for future examinations. 8. Seek to understand, not just memorise. Make sense of the terminology, which will help a lot as you try to understand the connections between different parts of the content necessary for conceptual understanding.

3 9744/J1H2/Promo/2021 Turn over Section A 1 Fats are usually stored as oil in the seeds of the plants and occasionally in the fleshy part of the fruit, as in the olive and the oil palm. The oil is a reserve of high-energy food for use by the germinating seed for growth of the embryo. The sunflower seed is actually the fruit of the sunflower (Helianthus annuus) and may contain about 51% oil. Fig. 1.1 shows a triglyceride molecule found in sunflower oil. (a) On figure 1.1, circle an ester bond. [1] Circle must include the two O atoms that are joined to a C atom (A: if all ester bonds correctly circled); (R: circle(s) that do not meet stated criteria). Examiner’s Comments: • Not always well answered, candidates are advised to use the above when attempting Biology questions as this is the accepted version of an ester bond in A level Biology. • Candidates are advised to put their circle carefully so as not to include the angular corners (red arrow) as these represent a C atom! Fig. 1.1 Fig. 1.1

4 9744/J1H2/Promo/2021 (b) Sunflower oil can be used to make biodiesel. During the process, the fatty acids in the triglyceride react with methanol to form fatty acid methyl esters that are liquid products. The other component of the original triglyceride molecule forms another liquid product that is denser than the methyl esters. Name the component of the molecule seen in Fig. 1.1 that forms this denser liquid. ……………………………………………………………………………………………………… [1] 1. Glycerol Examiner’s Comments: • Generally well-answered. • A number of candidates did not appear to be familiar with the components that make up a triglyceride molecule. (c) Table 1.1 shows the melting points of the three different fatty acid methyl esters. Table 1.1 (i) Complete Table 1.1 with one possible value for the melting point of methyl linoleate. [1] Accept any value from -20.1 oC to -54.9 oC; Note: The higher number of H atoms implies more saturation (less or no double bonds) of the fatty acid molecules and hence they have higher melting points ( -20 oC is a higher temperature than -55 oC). Since methyl linoleate has H atom numbers that is between that of the other two esters, its melting point is somewhere between the two values of -20 oC and -55 oC. Examiner’s Comments: • Generally well-answered with most candidates able to give a value between -200C and -550C. (ii) Suggest one way the structure of fatty acids found in butter might differ from the fatty acid that forms methyl oleate. …………………………………………………………………………………………………………. ……………………………………………………………………………………………………... [1] Compared to methyl oleate, 1. the fatty acids in butter may have no / less double bonds (A: reference to ‘ more saturated’); 2. the fatty acids in butter may contain many more carbon atoms; fatty acid methyl ester formula melting point / oC methyl linoleate C19H34O2 methyl linolenate C19H32O2 - 55.0 methyl oleate C19H36O2 - 20.0

5 9744/J1H2/Promo/2021 Turn over Note: Butter is a solid at room temperature compared to methyl esters, it is more saturated and hence has higher melting point. These saturated fatty acid molecules have straight fatty acid chains and thus pack more closely together and may be solids at room temperature. Methyl esters that have more double bonds (less H atoms) may have more ‘bent’ or ‘kinked’ fatty acid tails thus they may pack less tightly, leading to lower melting points and they are liquids. In biodiesel production higher melting point methyl esters (more saturated) do not have good flow properties as they tend to become a gel that impedes flow of biodiesel in engines. Examiner’s Comments: • Generally not well-answered. • A number of students were not certain that the fatty acid molecules in butter were likely to have more saturated carbon chains that enable closer packing and hence a higher melting point and are solids at room temperature. • Phrase to avoid: ‘There are more kinks in this molecule’ (Not precise: ‘Kinks’ are just bends in a molecule and these kinks could be due to a number of reasons). The specific reason for the presence of ‘kinks’ in methyl ester molecules is the presence of C=C double bonds, hence candidates must be specific in this! • Phrase to avoid: ‘The fatty acid chains in butter are saturated ’. (Not precise: This phrase is misleading as the methyl esters may also ha