TMJC 2020 Bio Prelim Paper 3 (Q)

Tampines Meridian Junior College 2020 JC2 Preliminary Examinations H2 Biology CANDIDATE NAME CIVICS GROUP _____________________________________________________________________________ H2 BIOLOGY 9744 Paper 3 Long Structured and Free Response Questions 18 September 2020 2 hours _____________________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name and Civics Group in the spaces at the top of the page. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all questions. Section B Answer ONE question. You may lose marks if you do not show your working or if you do not use appropriate units. 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. ______________________________________________________________________________________ This document consists of 17 printed pages and 1 blank page. For examiner’s Use Section A 1 / 32 2 / 18 Section B 3 or 4 / 25 Total / 75 TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2020 JC2 Preliminary Examinations H2 Biology Section A Answer all questions in this section. QUESTION 1 The cystic fibrosis transmembrane conductance regulator (CFTR) protein is an ion channel. In the lung, the CFTR ion channel moves chloride ions from inside the cell to outside the cell. Cystic fibrosis (CF) is a serious genetic condition caused by recessive mutations in the gene for the CFTR protein. One of the most common mutated alleles of this gene is known as ΔF508, a deletion of the amino acid phenylalanine at the 508 th amino acid position of the polypeptide. This mutation results in a CFTR protein that does not conduct chloride ions. Features of CF, which are also observed in heterozygotes, include: • a reduction in water loss through epithelial cell membranes • a reduction in sweating. When there is less water outside the cells, the mucus in the airways becomes dehydrated and thickens, as shown in Fig. 1.1 . The cilia becomes unable to sweep properly when the mucus is thick as sticky mucus weighs them down. Because the cilia are unable to move properly, mucus gets stuck in the airways, making it difficult to breathe. In addition, germs caught in the mucus are no longer expelled from the airway, allowing them to multiply and cause infections. Thick mucus in the lungs and frequent airway infections are some of the most common problems that people with CF face. Fig. 1.1

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