2024 JPJC Prelim Biology P2 (Q)

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 31 printed pages and 1 blank page.

2 JPJC/JC2 H2 Biology/Prelim/2024 BLANK PAGE

3 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over 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. ........................................................................................................................ (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]

4 JPJC/JC2 H2 Biology/Prelim/2024 (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] (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 con sists 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 fla gella 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 per minute ........................................ [2]

5 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over (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]

6 JPJC/JC2 H2 Biology/Prelim/2024 (ii) The researchers concluded that some of the regrowth uses protein molecules already present in the cell. Explain the evidence for this conclusion. ........................................................................................................................ ................................................................................................................... [2] [Total: 12]

7 JPJC/JC2 H2 Biology/Prelim/2024 [Turn over Question 2 starts on page 8.

8 JPJC/JC2 H2 Biology/Prelim/2024 2 Enzymes have important roles in living organisms. Fig. 2.1a shows lactase, a cruci al 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 catalyti c portion 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

9 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. ........................................................................................................................ ........................................................................................................................ (ii) Suggest reasons why lactase is anchored with the catalytic portion extending into the intestinal lumen. ........................................................................................................................ ................................................................................................................... [2]

10 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