2022 EJC Promo JC1 P2 Bio (A)

©EJC 2022 9744/ J1H2Promotional Examination /2022 [Turn over EUNOIA JUNIOR COLLEGE JC1 Promotional Examination 2022 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME ANSWER KEY CIVICS GROUP 2 2 - REGISTRATION NUMBER H2 Biology 9744 / 02 04 October 2022 2 hours Additional Materials: 12-page Answer Booklet. READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. 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. At the end of the examination, submit the Question Booklet and the 12-page Answer Booklet separately. This document consists of 22 printed pages. For Examiner’s Use Section A 1 2 3 4 5 Section B 6 Total 80

2 ©EJC 2022 9744/J1H2Promotional Examination/2022 Section A Answer all questions in the spaces provided. 1 Fig. 1.1 shows the process of collagen synthesis in a fibroblast cell. Fig. 1.1 (a) With reference to Fig. 1.1, describe how procollagen is transported out of the cell. [3] 1. Secretory vesicle containing procollagen buds off from the trans face of the Golgi apparatus; 2. Moves along microtubules towards cell surface membrane; 3. Membrane of the secretory vesicle fuses with the cell surface membrane by and procollagen is released out of the cell via exocytosis; Comments Majority of students did not read the question properly and wasted time writing about how procollagen was synthesised (i.e. details of transcription and translation). The question is only concerned with how procollagen is transported out of the cell, not how procollagen is made. Also, students need to be careful in differentiating between procollagen and collagen. Question’s focus is on procollagen, not collagen. Point 1 • R: transport vesicle / Golgi vesicle • R: pinch off. “Pinch off” does not have the same meaning as “bud off”. • It is incorrect to say that a protein/procollagen buds off from the Golgi apparatus. The term “buds off” is used to describe how a vesicle is formed, not the protein. • Students need to be aware to use a capital “G” when spelling “Golgi”.

3 ©EJC 2022 9744/ J1H2Promotional Examination /2022 [Turn over Point 2 • Many students failed to earn a mark here due to the lack of mention o f the involvement of microtubules. Point 3 • A number of students failed to earn a mark here due to the lack of mention of “exocytosis” as the transport process. (b) The primary structure of a collagen polypeptide has a repeating pattern of three amino acids. Fig. 1.2 shows the two forms of this pattern. Fig. 1.2 Hydroxyproline is a proline molecule that has a hydroxyl ( -OH) group added to its R -group. The hydroxyl groups are involved in hydrogen bonding in tropocollagen. Glycine makes up approximately 30% of the total amino acid composition of collagen. Explain how the structure of glycine plays an essential role in contributing to the high tensile strength of tropocollagen. [3] 1. Glycine is the amino acid with the smallest R-group; 2. This allows the formation of a tight triple helix / allow the three polypeptide to be closely associated; 3. This in turn allows for hydrogen bonds to be form between the 3 polypeptides in the triplex helix, contributing to high tensile strength; Comments Point 1 • A number of students did not seem to know the structure of glycine, and incorrectly mentioned that glycine has hydroxyl group. • Students need to note that the R group of glycine is not involved in the formation of hydrogen bonds. • A number of students incorrectly mentioned that glycine is “one of the smallest amino acids”. This does not carry the same meaning as saying glycine is the smallest amino acids. Point 2 • R: compact triple helix. “compact’ and “tight” do not have the same meaning. • A number of students did not seem to have a clear idea of how to use / how not to use the term “tropocollagen” or “collagen molecule”. A collagen molecule is essentially termed as tropocollagen, an tropocollagen has 3 polypeptides chains wound around each other to form a triple helix. It is therefore incorrect to say that “glycine can fit in small spaces between tropocollagen molecules”, or that “glycine allow tropocollagen ti be packed closely together”. Point 3 • It is incorrect to describe hydrogen bonds as strong.

4 ©EJC 2022 9744/J1H2Promotional Examination/2022 (c) Many of the lysine amino acids in a collagen polypeptide also have a hydroxyl (-OH) group added to their R-group. Fig. 1.3 shows hydroxylysine. Fig. 1.3 (i) On Fig. 1.3, draw a box around the R group of hydroxylysine. [1] Comments A surprising number of students were not able to indicate the R group correctly. The hydroxyl group of hydroxylysine is important as a possible attachment site for a β-galactose molecule. The joining of β-galactose to hydroxylysine involves the formation of a glycosidic bond. The molecular structure of β-galactose is shown in Fig. 1.4. Fig. 1.4 (ii) Show how a glycosidic bond could be formed between carbon 1 of β -galactose and the R group of hydroxylysine. [3] 1. Show interacting parts of galactose and hydroxylysine (dotted box) + structure of galactose and hydroylysine drawn correctly (R: only R group drawn) 2. Condensation reaction + H2O 3. Final product drawn correctly + correct labelling of glycosidic bond (R: alpha glycosidic bond) Comments Some students did not seem to understand the command word “show how”, and only drew the final product. [Total: 10]

5 ©EJC 2022 9744/ J1H2Promotional Examination /2022 [Turn over 2 In human retinal photoreceptor cells, the EGFLAM gene codes for a protein known as Pikachurin. The production of this protein is depicted in Fig. 2.1 below. Fig. 2.1 (a) (i) Describe process Y. [3] 1. Process is splicing; 2. Spliceosome recognises and binds to splice sites at both ends of each intron; 3. Introns are then cut out / excised that will be degraded and exons are spliced / joined together by the spliceosome; Comments: • Most students correctly identified and described process Y in detail. • A small number of students did not name process Y, or mistakenly identified it as alternative splicing even though it was not depicted in Fig. 2.1. • Some students named process Y as “mRNA splicing” or “pre-mRNA splicing”; do take note that the proper term is RNA splicing. • Some also failed to mention the involvement of the spliceosome, or its function in splicing. process X process Y

6 ©EJC 2022 9744/J1H2Promotional Examination/2022 (ii) Contrast DNA replication with process X. [4] 1. [Enzyme involved in synthesis of product] DNA replication is carried out by DNA polymerase while transcription is carried out by RNA polymerase; 2. [Monomer of nucleic acid strand formed] Deoxyribonucleotides are joined together in DNA replication while ribonucleotides are joined together in transcription; 3. [Identity of nucleic acid strand formed] Two (identical) DNA molecules are produced during DNA replication whereas a single RNA molecule is produced during transcription; 4. [Nature of nucleic acid strand formed] The product of DNA replication is double- stranded DNA while the product of transcription is