2025 NYJC H2 Bio 9744 P2 MS

9744 / H2 Biology / 02 NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS BIOLOGY 9744/02 Paper 2 Structured Questions 15 September 2025 Candidates answer on the Question Paper. No Additional Materials are required. 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do no use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. 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 no 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. For Examiner’s Use 1 10 2 8 3 10 4 10 5 11 6 10 7 10 8 10 9 10 10 6 11 5 Total 100 This document consists of 27 printed pages and 2 blank pages. [Turn over H

9744 / H2 Biology / 02 2 Answer all the questions in this section. 1 In the majority of cell types, ribosomes are the most common organelle. They are found in the cytoplasm of bacterial and eukaryotic cells. [2024 H1 A Levels] (a) (i) List the two types of biomolecule that are found in ribosomes. Protein, ribosomal RNA /ribonucleic acid [1] (ii) State one difference between the ribosomes found in the cytoplasm of bacteria and the ribosomes found in the cytoplasm of eukaryotes. Bacteria have 70s ribosomes whereas eukaryotes have 80s ribosomes. [1] (iii) State two differences, other than differences in ribosomes, between typical bacterial cells and typical eukaryotic cells. 1. Bacterial cells have peptidoglycan cell wall whereas eukaryotes have cellulose cell wall. 2. Bacterial cells have circular DNA whereas eukaryotic DNA is linear 3. Bacterial cells lack nucleus/membrane bound organelles whereas eukaryotes have. [2] (b) Scientists have estimated the numbers of ribosomes found in cells. Fig. 1.1 is an electronmicrograph showing ribosomes in a cell. x67700 Fig. 1.1

9744 / H2 Biology / 02 3 (i) Suggest why it is difficult to use electronmicrographs, such as that shown in Fig. 1.1, to determine the total number of ribosomes in a cell. 1. Too many ribosomes to count which may cause inaccuracy in counting 2. Difficult to distinguish individual ribosomes as some are clustered together 3. Limited field of view capturing a small section of the cell, which may not be a good representation of the ribosome density of the entire cell. [3] (ii) Fig. 1.2 shows data for the number of ribosomes present in cells of different volumes. Fig.1.2 Describe and explain the relationship shown in Fig. 1.2. 1. [describe] As the cell volume increases from 10-1.5 to 103.9 µm 3, number of ribosomes per cell increases from 101.9 to 106.9 [explain] 2. The greater the volume of the cell, the more physical space to accommodate more ribosomes within the cell. 3. The greater the cell volume, the larger the cell size. Hence cell needs more ribosomes to synthesize proteins to carry out cellular activities for growth. [3] [Total: 10]

9744 / H2 Biology / 02 4 2 In 1953, James Watson and Francis Crick published details about the structure of DNA. They used experimental results from other scientists to help them work out the structure and then built a model of a section of a DNA molecule, using pieces of wire and met al, with clamp stands to hold the model in place. This is shown in Fig. 2.1. Fig. 2.1 (a) Watson and Crick used results from work carried out by Erwin Chargaff. He found that the proportions of the bases A, T, C and G were different in different species, but within each species: • the proportion of A was equal to the proportion of T • the proportion of G was equal to the proportion of C. (i) Name the bases A, T, G and C. A adenine T thymine C cytosine G guanine [2] all correct = 2 marks one, two or three correct = 1 mark (ii) Suggest and explain how Chargaff’s findings helped Watson and Crick work out the structure of DNA. 1. complementary base pairing between… 2. Adenine and Thymine, Guanine and Cytosine 3. hydrogen bonding between base pairs/ holding two strands together 4. idea of fixed diameter at 2nm with two ring base pair with one ring base / purine with pyrimidine 5. double helix with two DNA strands/polynucleotides 6. two strands are antiparallel [3]

9744 / H2 Biology / 02 5 (b) Phoebus Levene isolated the nucleotides of DNA and identified the carbohydrate component of each nucleotide. State the name of this carbohydrate component. Deoxyribose; [1] (c) Before the discovery of the structure of DNA as the molecule of inheritance, scientists thought that proteins were most likely to be the molecules that carried information. Suggest how the structure of proteins made scientists think that these were the molecules that carried information. 1. proteins are made of specific sequence of amino acids 2. there are up to 20 different amino acids in proteins 3. different proteins have different sequence of amino acids 4. idea that there is a great variety in protein structure [2] [Total: 8]

9744 / H2 Biology / 02 6 3 Leber Congenital Amaurosis (LCA) is an inherited eye disease. In LCA, the photoreceptor cells in the retina die at an early age. This causes impaired vision (reduced eyesight) in children, which can progress to blindness. LCA10 is a different form of LCA caused by a recessive mutation in the CEP290 gene. This gene codes for the protein CEP290, which is involved in the correct functioning of photoreceptor cells in the retina. This mutation in CEP290 occurs in the intron and causes an error to be made when the primary transcript is spliced to form messenger RNA (mRNA). The abnormal mRNA that is formed has an extra sequence of RNA nucleotides, known as exon X, between exon 26 and exon 27. Exon X contains a STOP codon. Fig. 3.1 compares the effect of the mutation in CEP290 with the normal gene expression Fig. 3.1 CEP290 is a classic example of intronic mutation, changes in sequences that occur to non - coding DNA. (a) Define what is non-coding DNA. portions that do not encode protein or RNA [1] (b) Describe the structure and functions of another two types of non -coding DNA in eukaryotes. including centromeres, telomeres, promoters, enhancers and silencers [4]

9744 / H2 Biology / 02 7 In 2022, research was carried out into possible treatment of LCA10 using genetic technology. A human clinical trial investigated a treatment of LCA10 using a short RNA nucleotide sequence known as Sepofarsen. Sepofarsen binds to the section of the primary transcript containing the CEP290 mutation. (c) With reference to the above method, identify the level in which gene regulation is achieved and describe two other methods to regulate gene expressio n at this level and the ir respective functions. 1. Post-transcriptional level 2. Addition of 7-methylguanosine (7-MG) to the 5’ end of the pre-mRNA 3. Addition of stretch of adenine nucleotides at the 3’ end of the pre -mRNA/ polyadenylation Function of 5’ GTP cap and 3’ poly(A) tail 4. 5’ GTP cap protects the mRNA from degradation 5. 3’ poly (A) tail prolongs the half -life of mRNA by buffering the mRNA against degradation 6. Both facilitates the export of mature mRNA from