NJC 2023 H2 Biology Prelim P3 Ans

©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination [Turn over NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME BIOLOGY CLASS 2bi2___ REGISTRATION NUMBER BIOLOGY Paper 3: Long Structured and Free-response Questions Candidates answer on the Question Paper and Answer Booklet No Additional Materials are required. 9744/03 25 August 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name and Biology class 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. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question in the Answer Booklet. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your workings or if you do not use appropriate units. The number of marks is given in the brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 /30 2 /10 3 /10 Section B 4/5 /25 Total /75 This document consists of 14 printed pages and 2 blank pages.

2 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination Section A Answer all the questions in this section. 1 FoxO1 is a protein found in pancreatic β cells. Fig.1.1 shows a model of FoxO1. Fig. 1.1 (a) Describe how monomers may be linked together to form the FoxO1 polypeptide chain. Peptide bonds formed between amino and carboxyl groups; Condensation reaction; Removal of water molecules; Make bottom border for writing. [2] (b) Explain how amino acids that are spaced far apart in the Fox O1 polypeptide chain may be brought together in its 3-dimensional structure. Stretches of amino acids in the polypeptide chain first adopt/fold/coil into a regular, recurring shape/repeating pattern [OR ref to localized folding of polypeptide backbone into secondary structures]; such as α-helix; [Beta sheet not seen in Figure] These secondary structures are stabilized by hydrogen bonds formed between the –C=O and –NH groups of the peptide bonds/backbone; The secondary structures extensively/further folds to form a specific three-dimensional globular structure, bringing amino acids that were spaced far apart in the linear chain to be close together in the tertiary structure; This tertiary structure is maintained by interactions between the R-groups of amino acids; Ref to hydrogen bonds, ionic bonds, disulphide bonds and hydrophobic interactions (At least 2);

3 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination [Turn over [4] Diabetes is often associated with the failure of the β (beta) cells in the pancreas, but it is unclear what actually causes this failure. Some studies have suggested that this failure may be related to FoxO1. A study was conducted using mice lacking the gene for FoxO1 in β cells (IKO) as well as normal (control) mice. Blood glucose levels after fasting were compared for four groups of mice: young (3 months old) male mice, young (3 months old) female mice, older females (who have had several pregnancies) and aging males (16–20 months). The results are shows in Fig. 1.2. Fig. 1.2 (c) Describe and explain the blood glucose levels after fasting between young control mice and young IKO mice without FoxO1. similar/same/nearly same (means)/very small difference/both at a low level; means/averages (all) close to 0.8 mg ml–1; differences not (statistically) significant; similar/same/nearly same range/spread of data; lack of FoxO1/IKO/fewer beta cells does not affect/has little effect on blood glucose/sugar; All marking points are comparisons between control and IKO mice. Do not award marks for comparisons between male and female mice.

4 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination [3] (d) Aging and having pregnancies are considered to be physiological stresses. Describe and explain the effect of stress on blood glucose levels in control mice. stress causes marginal increase (in mean blood glucose/sugar); older mice/males/females / aging mice show slight increase compared to IKO [Ref to appropriate data] Stress reduces FoxO1 expression only slightly compared to IKO; Fox01 regulates/maintains sensitivity to changes in glucose levels; OR stress causes increase (in mean blood glucose/sugar); older mice/males/females / aging mice show increase [Ref to appropriate data] Stress reduces expression of FoxO1; Fox01 regulates/maintains sensitivity to changes in glucose levels; Make bottom border for writing. [3]

5 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination [Turn over (e) Insulin and glucagon are hormones that are synthesi sed by pancreatic cells and secreted into the bloodstream in response to changes in blood glucose concentration to maintain homeostasis. Explain how such newly synthesi sed hormones are processed and released into the bloodstream by pancreatic cells. Hormone polypeptide chains begin folding after being inserted into the ER lumen; Polypeptides undergo initial post-translational modification in the RER; Transported from RER to cis face of Golgi apparatus via transport vesicles; Undergo post-translational modification in Golgi apparatus; Bud out from trans face of Golgi apparatus in secretory vesicles; [Max 1m for reference to PTM] [Max 3m] AND Secretory vesicles fuse with cell surface membrane to release polypeptide chains by exocytosis; [Max 1m for reference to PTM] Make bottom border for writing. [4] The levels of pancreatic hormones and β cell mass in older female control mice and older female IKO mice lacking FoxO1 were then investigated. The results are shown in Fig. 1.3. Fig. 1.3

6 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination (f) Calculate the percentage difference in β cell mass of the IKO mice compared to the control mice. Show your workings and give your answer in three significant figures. 2.3-1.5; 0.8/2.3 X 100 = 34.78%; % [2] (g) Outline the relationship between lack of FoxO1 and levels of pancreatic hormones in mice. lack of FoxO1 (correlates) with low/decreased insulin; lack of FoxO1 (correlates) with high/increased glucagon levels; Make bottom border for writing. [2] (h) Using information from Fig. 1.2 and Fig. 1.3, deduce the relative levels of pancreatic hormones in young female control and IKO mice lacking FoxO1 Similar levels of insulin and glucagon/ pancreatic hormones; [OR] Slightly lower levels of insulin and slightly lower levels of glucagon compared to control mice; Make bottom border for writing. [1] To examine whether the changes observed were due to lack of β cell function or change in β cell number, investigators studied the following types of cells: • still producing insulin • newly formed β cells • no longer producing insulin. The results are shown in Fig. 1.4.

7 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination [Turn over Fig. 1.4 (i) State which group of cells showed the least change in the mice studied. newly formed β cells; Accept if newly formed beta cells in IKO mice but not in control mice only. Reject all answers apart from the first given and any comparisons between IKO and control mice, rather than between younger and older mice. [1]

8 ©NJC 2023 9744/03/SH2/H2/Biology/Preliminary Examination (i) Describe the effects of aging on the distribution of cell types in mice. newly formed β cells fewer/reduced/smaller % (in control/IKO mice); cells still producing insulin (slightly) more/increased/hig