2025 EJC JC2 Biology Prelim P3 - QP

©EJC 2025 9744/03/J2H2PRELIM/2025 [Turn over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examinations 2025 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 4 - REGISTRATION NUMBER H2 Biology Paper 3 Long Structured and Free-response Questions 9744/03 17 September 2025 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 18 printed pages and 2 blank pages. For Examiner’s Use Section A 1 2 3 Section B 4 OR 5 Total 75

2 ©EJC 2025 9744/03/J2H2PRELIM/2025 BLANK PAGE

3 ©EJC 2025 9744/03/J2H2PRELIM/2025 [Turn over Section A Answer all questions on the Question Paper. 1 Fig. 1.1 is a diagram showing the transcription of part of the CALD1 gene that codes for a protein known as caldesmon. The part of the CALD1 gene shown is a section of exon. Structure A represents an enzyme involved in transcription. Fig. 1.1 (a) (i) Name the enzyme labelled A in Fig. 1.1. ....................................................................................................................................... [1] (ii) Name the bond that forms between the nucleotides in the primary transcript. ....................................................................................................................................... [1] Table 1.1 shows the codons that correspond to some amino acids. Table 1.1 amino acid codons Phe UUU UUC Trp UGG Met AUG Thr ACU ACC ACA ACG Arg AGA AGG Val GUU GUC GUA GUG Gly GGU GGC GGA GGG (iii) State the amino acid sequence that is coded for by the sequence of nucleotides on the primary transcript shown in Fig. 1.1. ....................................................................................................................................... [1]

4 ©EJC 2025 9744/03/J2H2PRELIM/2025 (iv) Explain why one of the strands of DNA is not transcribed. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ....................................................................................................................................... [3] Caldesmon is a large protein with a number of binding sites to attach to other proteins. Caldesmon exists in two different forms, H-caldesmon and L-caldesmon. H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells. L-caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein. • Caldesmon is coded for by a gene known as CALD1. • CALD1 has 17 exons. • The primary structure of H-caledesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon. (b) (i) Researchers have discovered that a gene mutation is not the cause of the two different forms of caldesmon. Explain what is meant by a gene mutation. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ....................................................................................................................................... [2]

5 ©EJC 2025 9744/03/J2H2PRELIM/2025 [Turn over (ii) Researchers now known that the two different forms of caldesmon are the result of events occurring directly after transcription of DNA. Changes occur to the primary transcript that is formed by DNA transcription. Explain how the smooth muscle cells and non- muscle cells can produce different forms of caldesmon from the same primary transcript. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ....................................................................................................................................... [2] (iii) Suggest how the two different forms of caldesmon can still have similar functions, even though they have a different primary structure. ........................................................................................................................................... ....................................................................................................................................... [1]

6 ©EJC 2025 9744/03/J2H2PRELIM/2025 Caldesmon was recently reported in the scientific literature to be involved in gastric cancer progression, invasion, and migration. Tumour cells can become invasive through increased mobility and decreased adhesion, which can lead to metastasis from the primary tumour site. This process is triggered through changes in gene expression mediated by signalling pathways, including the PI3K-AKT pathway. Fig. 1.2 shows the PI3K-AKT signalling pathway, in which: • KRAS and RHEB are G-proteins. • PI3K, AKT, RAF, MEK, and ERK are all protein kinases. • Sharp arrows (↓) represent activation, while blunt arrows ( ┴ ) represent inhibition. Fig. 1.2 (c) (i) Other than signal amplification , describe one advantage of the PI3K -AKT signalling pathway using one example shown in Fig. 1.2. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ....................................................................................................................................... [2]

7 ©EJC 2025 9744/03/J2H2PRELIM/2025 [Turn over (ii) Using Fig. 1.2, describe a phosphorylation cascade that results in cell