2025 VJC H2 Biology Prelim P3 Answer

VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2025 HIGHER 2 NAME : ……………………………………………………….………………. CT CLASS: ………………..……… BIOLOGY Paper 3 Long Structured and Free-response Questions 9744 / 03 18/09/2025 2 hour Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name and CT 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 space provided on the Question Paper. 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 bracket [ ] at the end of each question or part question. Question Marks Section A 1 2 3 Section B Total This document consists of 20 printed pages. [Turn over]

1 (a) Outline the roles of oxygen in aerobic respiration. [3] • S erves as the final electron acceptor at the end of the electron transport chain in oxidative phosphorylation; • A llows continuous flow of electrons along the electron transport chain for continuous production of ATP in oxidative phosphorylation; • A llows the regeneration of NAD and FAD for link reaction and Krebs cycle to continue in the mitochondria; A ir contains a mixture of gases, which include approximately 78% nitrogen, 21% oxygen and 0.03% carbon dioxide. Fluctuations in these levels have occurred multiple times throughout the evolution of earth’s atmosphere. It is known that Earth was once without oxygen, but the gas began to accumulate in the atmosphere around 2.3 billion years ago. The increased presence of oxygen produces a more efficient energy source in the form of aerobic metabolism, producing 16-18 times more adenosine triphosphate (ATP) per hexose sugar than anaerobic metabolism. Multicellular organisms require efficient oxygen transport systems because the simple process of diffusion is too slow and inefficient to reach all cells within their large bodies, which have a small surface-area-to-volume ratio. Invertebrates like molluscs and arthropods make use of a protein called haemocyanin to transport oxygen throughout their bodies. It is an extracellular protein not contained within cells, but is instead dissolved freely in the haemolymph, which is the invertebrate equivalent of blood. Haemocyanin is made up of a dimer or hexamer of subunit proteins depending on the species, with each subunit containing two copper ions to bind to one oxygen molecule. Fig. 1.1 shows the structure of a haemocyanin subunit, as well as the arrangement of the oxygen binding site in haemocyanin made up of six histidine amino acid resid