2024 JPJC Prelim 9744 Biology P2 (A)(1)

9744 / 02 [Turn over NAME : CLASS : JURONG PIONEER JUNIOR COLLEGE JC2 Preliminary Examination 2024 BIOLOGY Higher 2 9744/02 27 August 2024 Paper 2 Structured Questions 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your class 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. 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 2 3 4 5 6 7 8 9 10 11 Total This document consists of 19 printed pages and 1 blank page.

2 JPJC/JC2 H2 Biology/Prelim/2024 Section A Answer all questions 1 (a) Fig. 1.1 shows a single-celled organism called Chlamydomonas. Fig. 1.1 (i) Name two structures that could be present inside the nucleus. [2] 1. nucleolus ; 2. DNA / rRNA / mRNA / chromatin / nucleosome / histones / ribosomal subunits (ii) Chlamydomonas lives in freshwater ponds. It uses its flagella to swim towards light of moderate intensity but away from very bright light. Using information in Fig. 1.1, explain the advantage of this behaviour. [2] 1. (compulsory) Presence of chloroplast in Chlamydomonas, allowing Chlamydomonas to photosynthesise ; 2. moves to optimum/best light intensity for photosynthesis ; OR 3. avoids damage to photosynthetic pigments due to very bright light ;

3 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over (iii) Oligosaccharides are carbohydrates that contain three to ten monomers in their chain. Chlamydomonas use oligosaccharides to synthesise glycoproteins, which are transported to cell surface membranes. Describe the roles of the rough endoplasmic reticulum and the Golgi body in synthesising glycoproteins. [2] rough endoplasmic reticulum 1. Site of polypeptide/protein synthesis ; 2. polypeptide folding (in lumen and packaged in transport vesicles to Golgi body); A protein folding Golgi body 3. protein is further modified, sorted and packaged (into secretory vesicles in the lumen/cisternal space of Golgi body) ; rough endoplasmic reticulum or Golgi body 4. Proteins will undergo biochemical modifications including phosphorylation / glycosylation / attachment of, oligosaccharide / polysaccharide / carbohydrate ; (b) A Chlamydomonas cell has two flagella. These flagella contain a single type of protein. A flagellum consists of a bundle of 242 filaments. Each filament consists of 7500 protein molecules. Each protein molecule contains 900 amino acid units. In an investigation, a culture of Chlamydomonas was treated in a way that caused them to lose their flagella without any other damage to the cells. The flag ella grew back to their original length in 60 minutes. How many amino acid molecules would be incorporated into each growing flagellum per minute? Show your working. amino acid molecules incorporated = 242 𝑥 7500 𝑥 900 60 ; = 27 225 000 amino acid molecules incorporated per minute 27 225 000 ; [2]

4 JPJC/JC2 H2 Biology/Prelim/2024 (c) The researchers investigated the rate at which the flagella grew in two dif ferent media. 1 a medium containing puromycin, which prevents translation by attaching to ribosomes 2 a control medium The results are shown in Fig. 1.2. Fig. 1.2 (i) Describe how the rate of growth was affected by puromycin. [2] 1. In the presence of puromycin, the rate of growth is (slightly) lower / slower, in the first 27 minutes than the control ; Or 2. In the presence of puromycin, the max rate of growth of flagellum is 1.2um per min, lower than the control at 1.5um per min ; 3. As time increase from 27 min to 60 min, the rate of growth in the presence of puromycin decreases / is much lower than the control ;

5 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over (ii) The researchers concluded that some of the regrowth uses protein molecules already present in the cell. Explain the evidence for this conclusion. [2] 1. (re)growth only slightly affected by puromycin in the first 27 min ; 2. since protein synthesis was inhibited, growth continued hence it is likely to be using proteins present ; [Total: 12]

6 JPJC/JC2 H2 Biology/Prelim/2024 2 Enzymes have important roles in living organisms. Fig. 2.1a shows lactase, a crucial enzyme in the human digestive system produced by enterocytes. It is located on the surface of the microvilli, specifically within the brush border membrane. Fig 2.1b shows the enzyme anchored at its C-terminal end, with the catalytic por tion extending into the intestinal lumen. This strategic positioning enables lactase t o efficiently catalyse the cleavage of lactose, the major carbohydrate in milk, into its constituent absorbable monosaccharides, glucose and galactose. Lactase's function is vital for the nourishment of newborn mammals, whose primary source of nutrition is milk. Fig. 2.1a Fig. 2.1b

7 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over (a) The enzyme lactase is made up of 1023 amino acids. Fig. 2.2 shows the positions in the polypeptide chain of five amino acids found at the active site of lactase. Fig. 2.2 (i) With reference to the information in Fig. 2.1 and Fig. 2.2, describe how amino acid residues at different positions in lactase may be brought together in the active site when lactase is synthesised by the cell. [3] 1. The polypeptide chain coils and folds into the (geometrically regular repeating) secondary structures / α-helix and β-pleated sheet respectively ; 2. stabilised by hydrogen bonds between C=O and –NH groups in the (main chain of the) polypeptide / backbone ; 3. The polypeptide chain / secondary structure is further bent, coiled and folded , to form the specific 3D conformation / tertiary structure / globular structure, of lactase, with the 5 amino acids brought together at the enzyme active site ; 4. Maintained by hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions (any 2) between the R groups of amino acids ; (Max 3) (ii) Suggest reasons why lactase is anchored with the catalytic portion extending into the intestinal lumen. [2] 1. Direct Access: This allows the lactase to be in contact with lactose present in lumen 2. Efficiency: Maintains stable positioning for optimal catalytic activity / break down lactose efficiently. 3. Proximity: Ensures immediate uptake of glucose and galactose by enterocytes. 4. Protection: Prevents degradation by proteolytic enzymes. 5. Localisation: Ensures activity where lactose digestion occurs in the small intestine.

8 JPJC/JC2 H2 Biology/Prelim/2024 (b) People with lactose intolerance can drink lactose-free milk. Lactose-free milk is produced by treating milk with lactase. There are two ways of removing lactose from milk: ● mixing a solution of lactase with the milk (free lactase) ● enclosing the lactase inside permeable beads and pouring the milk over them (immobilised lactase). Fig. 2.3 shows these two methods. Fig. 2.3 Table 2.1 shows the effect of pH on the activity of free lactase and immobilised lactase. Table 2.1 pH activity of free lactase / a.u. activity of immobilised lactase / a.u. 2 0 0 3 0 38 4 75 75 5 94 98 6 63 76 7 56 63 8 28 35

9 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over Explain the effects of pH on the activity of these two enzymes. [5] Describe optimum