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 into collagen fibres; Max.2 (ii) With reference to Fig. 1.1, explain how changes in collagen affect the skin as a person ages. [2] 1. Less dense collagen fibres; 2. Broken collagen fibres; 3. loss of tensile strength / loss of support to skin; 4. Skin is saggy / uneven / folded; R: dark spots on skin as collagen has no effect on colour [Total 10] epidermal layer under epidermal layer

4 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 2 (a) Describe the roles of membranes within a cell. [2] 1. Selective barrier; 2. Regulating movement of substances in & out of organelles; 3. Site of formation of multi-enzyme complexes; 4. To increase the rate of reaction as enzymes are organised in sequence; 5. Compartmentalisation; 6. Provides localised environment to facilitate metabolic processes occurring simultaneously; 7. Maintain high concentrations of specific enzymes and substrates; 8. Prevents intermediates of one pathway from interacting with another; 9. Isolates harmful substances from the rest of the cell; Max. 2 ATP synthesis is catalysed by the enzyme ATP synthase. The process involves the coupling of H + ion movement through ATP synthase with the catalysis of ATP formation. Fig. 2.1 shows a diagram of ATP synthase in a mitochondrion. Fig. 2.1 inner membrane of mitochondrion β-subunits involved in catalysis of ADP & Pi to ATP H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

5 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 (b) Describe how H+ ions are moved across the membrane in Fig. 2.1. [2] 1. Facilitated diffusion; 2. H + ions move from intermembrane space to matrix; 3. Across hydrophilic channel provided by ATP synthase; 4. Down concentration gradient; 5. No expenditure of ATP; Max. 2m ATP synthase is found in all living organisms because ATP synthesis is an essential process for survival. ATP synthase is therefore one of the most conserved proteins in all living organisms including prokaryotes and animals. More than 60% of the amino- acid residues of the β-subunit are the same in all living organisms across Kingdoms. Fig. 2.2 shows the effect of increasing ADP concentration in different mixtures A , B and C. Their contents are shown below: • Mixture A contains substrates and ATP synthase from prokaryote or animal. • Mixture B contains substrates, an inhibitor and ATP synthase from prokaryote. • Mixture C contains substrates, an inhibitor and ATP synthase from animal. The inhibitor used for B and C are the same. Data used to plot the graphs were normalised to allow for comparison. Fig. 2.2 (c) Using information provided in this question, explain how the data in Fig. 2.2 shows the change in binding affinity of ATP synthase to ADP across the Kingdoms and why certain amino-acid residues in the β -subunit must be conserved. [4] 1. Binding affinity of ATP synthase to ADP decreases from prokaryote to animal;; 2. As higher ADP concentration required; rate of ATP synthesis ADP concentration A C B

6 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 3. To overcome binding of ATP synthase active site (to competitive inhibitor); [Accept alternate argument on higher rate at each ADP conc.] These amino-acid residues are conserved because 4. They are catalytic residues; 5. Involved in formation of phosphoester bond; OR 6. They are contact residues; 7. involved in binding to ADP; OR 8. Residues involved in maintaining (shape of) active site; 9. Complementary to ADP; If residues are changed 10. unable to produce ATP for essential cellular activities; 11. Organisms die / do not survive; (d) ATP synthase facilitates both the transportation of H + ions and the production of ATP. Describe two features that are similar between the processes. [2] 1. Specificity of channel of ATP synthase to H+ ions and active site of ATP synthase to ADP;; 2. The higher the concentration of substance, i.e. proton or ADP, the higher the rate of transport across membrane and rate of ATP synthesis respectively;; 3. AVP;; Max. 2 [Total 10]

7 River Valley High School 2023 JC2 Preliminary Examination H2 Biology 9744/02 3 In a developing oocyte, mRNAs are synthesized and then exported to the cytoplasm. However, these mRNAs are not immediately translated but are stored in the cytoplasm for future use in a zygote. Fig. 3.1 shows the changes to the 3’ end of a mature mRNA in a zygote starting from 20 minutes after fertilisation and the corresponding amount of protein synthesized. key     Fig. 3.1 (a) With reference to Fig. 3.1, explain the relationship between the length of poly(A) tail of the mRNA and the concentration of protein produced. [3] 1. When length of poly(A) tail is <50 nucleotides long, no protein wa