MI 2023 J2 H2 BI Prelim P2 ANS

Class Adm No Candidate Name: ___________________________________ This question paper consists of 27 printed pages, including 1 blank page. [Turn over] 2023 End-of-Year Examination Pre-University 3 H2 Biology 9744/02 Paper 2 Structured Questions 12 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your Admission number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the question booklet. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. For Examiner's Use Section A 1 /10 2 /9 3 /10 4 /12 5 /10 6 /13 7 /11 8 /12 9 /5 10 /8 Total /100

2 9744/02/PU3 EOY/2023 Answer all questions in this section. 1. Biomolecules function as building blocks for macromolecules to be assembled. Carbohydrate is made up of many monosaccharides and can be found in both animals and plants. (a) Name the bond formed between monomers in cellulose. ……………………………………………………………………………………………… [1] (b) Illustrate with a labelled diagram how two monomers form the bond in (a) in cellulose. Circle the bond formed between the two monomers. Fig. 1.1 shows the partial structure of the monomer. Fig. 1.1 [4] Β-(1,4) glycosidic bond; 1. Label: β -glucose, water, β(1,4) glycosidic bond 2. Circle glycosidic bond; 3. Water released as by-product; 4. Rotation of monomer; 5. Correct structure of cellobiose;

3 9744/02/PU3 EOY/2023 [Turn Over] (c) One of the defining features of all cells is the cell surface membrane. This membrane is composed of phospholipid bilayer, with other biomolecules dispersed throughout the bilayer. (i) Describe the roles of carbohydrates in the cell surface membrane. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………….. [2] (ii) During the synthesis of phospholipid, the phospholipid sometimes needs to be moved between the layers. The movement is facilitated by a transmembrane protein called floppase. Fig.1.2 shows floppase moving a phospholipid from the inner layer to the outer layer of the cell surface membrane. Fig. 1.2 Due to their hydrophilic heads, phospholipid molecules cannot cross the hydrophobic region of the membrane from the inner layer to the outer layer without floppase. Using your knowledge of proteins, suggest how the structure of floppase allows phospholipids to cross the hydrophobic region of the membrane. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………… [3] [Total :10] 1. The interior channel of floppase is lined with amino acids with hydrophilic R-groups forming a hydrophilic channel; 2. Contains a binding site that is complementary to the 3D structure of phospholipids that allows it to transport only phospholipids; 3. The exterior of floppase is lined with amino acids with hydrophobic R-groups; 4. To allow floppase to be embedded in the membrane via hydrophobic interactions with the hydrophobic fatty acid tails; The carbohydrates portion of glycolipids and glycoproteins are involved in 1. cell-cell recognition, (idea of) which is the ability of a cell to determine if other cells it encounters are (idea of) alike or different from itself; 2. cell-cell adhesion, (idea of) where the two adjacent cells may (idea of) bind with each other , causing adhesion between the cells. This enables cells to orientate and form a tissue. 3. G lycoproteins can act as cell surface receptors that are embedded or attached to the cell surf ace membrane and have a binding site for specific ligands;

4 9744/02/PU3 EOY/2023 2. Catalase is an enzyme that catalyses the decomposition of hydrogen peroxide, which is a toxic product of metabolism. A scientist investigated the activity of two forms of catalase, P and Q, extracted from Anopheles gambiae, an important vector of malaria. The scientists investigated the effect of increasing concentration of hydrogen peroxide on the activity of these two forms of catalase. The results are shown in Fig. 2.1. Fig. 2.1 (a) With reference to Fig. 2.1, describe and explain the effect of increasing concentration of hydrogen peroxide on the activity of catalase P. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………… [4] Describe [2 marks] 1. As concentration of hydrogen peroxide increases from 0mM to 100mM, activity of catalase increases steeply from 0a.u. to 120 a.u;OR 2. As concentration of hydrogen peroxide increase from 0-50mM, activity of catalase increase steeply from 0-96a.u , 50-100mM of H2O2, increase in decreasing rate, 96-120a.u; OR 3. As concentration of hydrogen peroxide increases from 100mM to 250mM, activity of catalase increases gently from 120a.u. to 130 a.u; 4. As concentration of hydrogen peroxide increases from 250mM to 300mM, activity of catalase remains at plateau at around 130/132 a.u; Explain [2 marks] 5. At low/increasing concentration of hydrogen peroxide, hydrogen peroxide/substrate is the limiting factor;OR 6. Active site of catalase/enzyme is available to bind to substrate/hydrogen peroxide; 7. At high concentration of hydrogen peroxide, enzyme/catalase is the limiting factor;OR 8. Active site of catalase/enzyme is saturated/mostly occupied by substrate;

5 9744/02/PU3 EOY/2023 [Turn Over] (b) Each molecule of catalase consists of four identical polypeptides. The two forms of catalase in Anopheles gambiae differ by only one amino acid at position 2 in the amino acid sequence. Explain how the difference in one amino acid sequence is responsible for the lower activity of catalase Q compared with catalase P. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………… [3] (c) Female mosquitoes feed on blood in order to produce their eggs. After feeding, the metabolic rate increases for egg production. The scientist allowed female mosquitoes to feed on blood. They found that female mosquitoes with only catalase P produced more eggs than those with only catalase Q. Suggest why there is a difference in egg production between the two types of Anopheles gambiae. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………… [2] [Total :[9] 1. Amino acid at position 2 is part of the active site of enzyme; [compulsory] 2. R group of the 2 amino acids are different with different properties; 3. Therefore, different folding of polypeptide/secondary structure/tertiary structure and give rise to different 3D conformation of active site; 4. Binding of substrates to catalase P is more (idea of) efficient/higher affinity than to catalase Q; 1. Increased metabolic rate means increased production of