RVHS 2023 JC2 H2 Prelim P2 A

RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CENTRE NUMBER S CLASS 22J INDEX NUMBER BIOLOGY 9744/02 Paper 2 Structured Questions 13 September 2023 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name 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 staples, paper clips, glue or correction fluid. DO NOT WRITE ON ANY BARCODES. Answer all questions in the spaces provided on the Q uestion Paper. 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 1 2 3 4 5 6 7 8 9 10 11 Total _____________________________________________________________________ This document consists of 28 printed pages.

2 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 Answer all questions. 1 Collagen is the dominant protein in extracellular tissues such as bone, skin, and other connective tissues. (a) (i) Name the most common tripeptide repeat in tropocollagen. [1] Glycine – Proline – Hydroxyproline / Hydroxylysine (ii) Explain the significance of the most common amino acid in the tripeptide repeat. [2] 1. Glycine is the smallest amino acid; 2. With hydrogen as the R-group; 3. Therefore glycine fits in the central core of the triple helix; 4. Resulting in tight coil / tightly packed helix; (iii) Compare between the hydrogen bonds with in tropocollagen and with in an alpha helix of a protein. [3] Similarities: 1. Both are between N-H and C=O of the polypeptide backbone;; 2. Both are occurring at regular intervals throughout the helix;; Max. 1m Differences: Feature Triple helix Alpha helix 1. Location of hydrogen bonds Between different polypeptide chain Within the same polypeptide chain;; 2. Amino acids forming the hydrogen bonds Between g lycine & hydroxlysine OR proline Between any amino acids;; 3. AVP;; Max. 1m

3 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 Fig 1.1 shows (a) diagrams of young and aged epidermal skin tissue and (b) the scanning electron micrographs of collagen fibrils under the epidermal layer of young and aged skin. young skin aged skin (a) (b) Fig. 1.1 (b) (i) Describe how collagen fibres are formed from tropocollagen. [2] 1. Staggered arrangement of tr opocollagen molecules; 2. Carboxyl (C) and amino (N) ends of different tropocollagen; 3. joined by covalent bonds; 4. Cross-linked to form fibrils; 5. which further assemble