2017 RVHS H2 Biology Prelims Paper 2 Answers

River Valley High School Pg 1 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION II CANDIDATE NAME CENTRE NUMBER S CLASS INDEX NUMBER H2 BIOLOGY 9744/02 Paper 2 Structured Questions 11 Sep 2017 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 IN ANY BARCODES. Answer all questions in the spaces provided on the Question 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 / 9 2 / 13 3 / 8 4 / 10 5 / 12 6 / 15 7 / 10 8 / 11 9 / 12 Total / 100 _____________________________________________________________________ This document consists of 24 printed pages.

River Valley High School Pg 2 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II Answer all questions. 1 Fig. 1.1 shows an electron micrograph of part of a plant cell. Fig. 1.1 (a) Identify region A and state its function. [2] 1. Stroma (of chloroplast);; 2. Site of light independent reactions / Calvin cycle;; (b) Describe how the structure of the membrane at B allows it to perform its function. [3] 1. (S) Large surface area of thylakoid membrane; 2. (F) Holds photosystems for light absorption / ETC for transfer of electrons; 3. (S) Thylakoid membrane impermeable to H +; 4. (F) Allows proton gradient to be generated (for chemiosmosis); 5. (S) Contains ATP synthase; 6. (F) For phosphorylation of ADP to ATP / ATP synthesis. Cyanobacteria are prokaryotic cells that are capable of carrying out photosynthesis. The

River Valley High School Pg 3 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II structure of a cyanobacteria is shown in Fig. 1.2. Fig. 1.2 (c) With reference to Fig. 1.1 and Fig. 1.2, compare the visible structures of cyanobacteria with that of C. [2] Similarities (1 max) 1. Both are bound by two membranes;; 2. Both have thylakoids;; Differences (1 max) Feature Chloroplast Cyanobacteria Grana Present Absent;; Intergranal lamellae Present Absent;; Cyanobacteria are considered to be the ancestors of structure C. They continued to function after being engulfed by primitive euk aryotic cells and evolved over time. This theory is known as the endosymbiont hypothesis. (d) State two features of structure C that provide support for this hypothesis. [2] 1. contains circular DNA;; 2. has 70S ribosomes;; 3. divides via binary fission;; [Total: 9]

River Valley High School Pg 4 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II 2 Fig. 2.1 shows the structure of a G-protein coupled receptor (GPCR). Fig. 2.1 (a) Describe how the structure of GPCR is adapted to its function. [3] 1. (S) The seven α-helices are mainly hydrophobic; 2. (S) can interact with the hydrocarbon tails of phospholipids via hydrophobic interaction; 3. (F) embeds GPCR in the cell surface membrane; 4. (S) has an extracellular binding site; 5. (F) for binding to complementary shape ligand; 6. (S) has an intracellular binding site / segment; 7. (F) (for binding to G protein) for activation of G protein; 8. (F) to transduce extracellular signals for activation of intracellular proteins / signal transduction; One of the cellular events resulting from glucagon binding to GPCR, shown in Fig. 2.1, is the activation of glycogen phosphorylase which breaks down glycogen to glucose. (b) (i) Describe how binding of glucagon leads to activation of glycogen phosphorylase. [3] 1. (binding of glucagon to ligand binding site on GPCR) causes conformation change of receptor; 2. GTP displace GDP in G protein; 3. activating it;

River Valley High School Pg 5 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II 4. and move along membrane to activate adenylyl cyclase; 5. Catalyse conversion of ATP to cAMP; 6. Activation of protein kinase A; 7. Activate phosphorylation cascade; (ii) Explain why liver cells store glucose in the form of glycogen. [3] 1. (large molecule) insoluble in water and will not exert osmotic or chemical influence on the cell;; 2. anomeric carbon is involved in glycosidic bond making glycogen stable and unreactive;; 3. extensively branched, hence is compact in shape;; The binding of glucagon to GPCR leads to an increase in blood glucose level partly due to the action of glucose transporters. Glucose transporters transport glucose via facilitated diffusion. (c) (i) Explain what is meant by facilitated diffusion. [2] 1. Net movement of glucose; 2. down concentration gradient; 3. via channel /carrier protein; 4. without additional investment of energy; (ii) Explain why glucose transporters are necessary to facilitate this process. [2] 1. glucose is polar;; 2. cannot diffuse across hydrophobic core; 3. of membrane/phospholipid layer; [Total: 13]

River Valley High School Pg 6 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II 3 Fig. 3.1 shows DNA replication in an Escherichia coli (A) and in a mammalian cell ( B). Diagrams are not shown to scale. A B Fig. 3.1 (a) State one way in which the DNA replication in these two organisms differs and explain the advantage of this to the mammalian cell. [2] 1. Single origin of replication in bacterium but multiple origin of replication in mammalian cell;; Accept: multiple replication sites / bubbles 2. Larger / longer DNA, speed up replication;; (b) Explain why DNA replication is said to be semi-conservative. [2] 1. Parental DNA strands separate / ref. to H bonds break; 2. Both strands acts as a template for synthesis of daughter strand; 3. Each daughter DNA molecule consists of one parental strand and one newly synthesised strand of DNA;; End replication problem is a fundamental problem associated with replicating DNA in eukaryotes. Some cells contain telomerase, which is responsible for extending the ends of DNA in eukaryotes. Fig. 3.2 shows the action of a telomerase enzyme.

River Valley High School Pg 7 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II Fig. 3.2 (c) Explain how the end-replication problem arises. [2] 1. due to the specificity of DNA polymerase; 2. the RNA primers complementary to the 3’ ends (of the template DNA); 3. cannot be replaced after their removal; 4. without a 3’ hydroxyl group on the DNA strand for DNA polymerase to add nucleotides to; (d) With reference to Fig. 3.2, state two differences between transcription and the process of lengthening of DNA ends. [2] Feature Lengthening of DNA Transcription Template RNA DNA Monomers DNA nucleotides RNA nucleotides Enzyme involved Telomerase RNA polymerase Product synthesised DNA RNA 1 mark for each comparative statement Any two [Total: 8]

River Valley High School Pg 8 of 23 Year 6 H2 Biology 9744 Paper 2 2017 Preliminary Examination II 4 Huntington’s disease is a rare neurodegenerative disorder targeting the central nervous system. Transcriptional dysregulation is one of the commonly observed molecular abnormalities affected in this disease. Recent evidence suggests the involvement of a mutant Huntingtin protein in the processes regulating condensation of DNA,