2024 EJC Prelim Biology P3 (Q)

©EJC 2024 9744/03/J2H2PRELIM/2024 [Turn over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2024 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 3 - REGISTRATION NUMBER H2 Biology Paper 3 Long Structured and Free-response Questions 9744/03 16 September 2024 2 hours Additional Materials: 12-page Answer Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. Write your answers in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue, or correction fluid/tape. Section A Answer all questions on the Question Paper. Section B Answer one question on the 12-page Answer Booklet provided. Write your answer to each part of the question on a fresh sheet of paper. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, ensure that you submit both the Question Paper and Answer Booklet. This document consists of 14 printed pages and 2 blank pages. For Examiner’s Use Section A 1 2 3 Section B 4 OR 5 Total 75

2 ©EJC 2024 9744/03/J2H2PRELIM/2024 BLANK PAGE

3 ©EJC 2024 9744/03/J2H2PRELIM/2024 [Turn over Section A Answer all questions on the Question Paper. 1 The development of a mouse from a fertilised egg into an adult is regulated by variations in DNA methylation. Fig. 1.1 shows the developmental stages of a mouse with corresponding levels of DNA methylation. R, S and T represent the zygote, blastocyst and embryo respectively. Fig. 1.1 (a) (i) Compare the features of a cell derived from the zygote with that from the inner cell mass of the blastocyst. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [3] developmental stage zygote blastocyst embryo egg cell zygote morula blastocyst embryo adult relative level of DNA methylation R T S sperm cell

4 ©EJC 2024 9744/03/J2H2PRELIM/2024 (ii) Explain how changes to DNA methylation from R to S bring about differentiation. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [4] (iii) At different developmental stages of the mouse, the control of the telomerase gene expression is crucial. Suggest if the telomerase gene in cells is likely to be methylated from T to an adult mouse. ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [1] (iv) Active telomerase can be found in some cell types in a mouse. Using a named example, explain the role of telomerase. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [3]

5 ©EJC 2024 9744/03/J2H2PRELIM/2024 [Turn over In an experiment, chromatin from various tissues were isolated and treated with DNase, an enzyme that degrades naked double-stranded DNA. After digestion, the enzyme was removed. Any remaining intact DNA was extracted and mixed with radioactively labelled DNA probes specific for certain genes, under conditions that favoured nucleic acid hybridisation. The levels of binding of the labelled DNA probes were measured. Some of the results are shown in Table 1.1 below. Table 1.1 Sample Tissue source of chromatin Gene radioactive DNA probe is specific to Percentage binding of radioactive DNA probe 1 Skeletal muscles Myosin gene 25 2 Pancreas Myosin gene 91 3 Skeletal muscles Chymotrypsin gene 93 (b) (i) Outline the steps between extraction of intact DNA and mixing with radioactively labelled DNA probes for nucleic acid hybridization. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [3] (ii) State two similarities between the probes used in the experiment and primers used in Polymerase Chain Reaction (PCR). ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [2] (iii) Suggest how DNA in the chromatin are protected from digestion by DNase. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [2]

6 ©EJC 2024 9744/03/J2H2PRELIM/2024 (iv) With reference to Table 1.1, explain which gene is more actively transcribed in skeletal muscle cells. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [2] (v) Explain one type of protein modification that supports your answer to (b)(iv). ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………...…………………………………………...………… [2]

7 ©EJC 2024 9744/03/J2H2PRELIM/2024 [Turn over Dystrophin is a cytoskeletal protein found in human muscles. The gene which encodes dystrophin has 79 exons. Mutations in this gene leads to Duchenne muscular dystrophy (DMD), which causes progressive muscle impairment in children. One of the most common mutations in the dystrophin gene, which occurs in exon 44, results in a non-functional protein. The asterisks (*) in Fig. 1.3 show the positions where del etions were detected in exon 44 and the reading frame is indicated by the boxes. To treat DMD, scientists modified the dystrophin gene by removing exon 44 , producing a partially functional protein. Fig. 1.3 (c) Explain how removal of exon 44 could result in production of a partially functional dystr ophin protein. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ………………...…………………………………………...……………………………………….… [3] Duchenne muscular dystrophy (DMD) is a X-linked recessive disorder. Mary and John are a normal, healthy couple without DMD who gave birth to their first-born son with DMD. They went for genetic testing and discovered that Mary is a carrier. (d) (i) Using suitable symbols, identify the genotypes of the following individuals. Mary: .................... John: .................... First-born son with DMD: .................... [2]

8 ©EJC 2024 9744/03/J2H2PRELIM/2024 (ii) Calculate the probability that their second child is also a son with DMD. [1] (e) Rare females with DMD have a translocation that disrupts the dystrophin gene on on e X chromosome and causes non-random inactivation of the normal X chromosome, resulting in the expression of the disease. Molecular characterization of the translocation junctions revealed reciprocal translocati on between the X chromosome and an autosome, with both deletion and addition of nu cleotides at the junction. Suggest how reciprocal translocation and non-random X-chromosome i