2025 NYJC H2 Bio 9744 P2 QP

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 2 3 4 5 6 7 8 9 10 11 Total 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. (a) (i) List the two types of biomolecule that are found in ribosomes. [1] (ii) State one difference between the ribosomes found in the cytoplasm of bacteria and the ribosomes found in the cytoplasm of eukaryotes. [1] (iii) State two differences, other than differences in ribosomes, between typical bacterial cells and typical eukaryotic cells. [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. [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. [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: T: C: G: [2] (ii) Suggest and explain how Chargaff’s findings helped Watson and Crick work out the structure of DNA. [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. [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. [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. [1]

9744 / H2 Biology / 02 7 (b) Describe the structure and functions of another two types of non -coding DNA in eukaryotes. [4] 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. [5] [Total: 10]

9744 / H2 Biology / 02 8 4 (a) Fig. 4.1 shows photomicrographs of individual cells from the root tip of an onion, Allium sp., at different times in the mitotic cell cycle. Fig. 4.1 (i) Place the letters representing the individual cells in the correct sequence of the mitotic cell cycle. The first letter has already been filled in. [2] (ii) Describe the events that occur in cell A. [3]

9744 / H2 Biology / 02 9 (iii) Colchicine is a chemical used by scientists to study mitosis. This chemical inhibits the organisation of the microtubules in prophase of mitosis. The cells shown in Fig. 4.1 had not been treated with colchicine. Explain the evidence in Fig. 4.1 that shows the cell s had not been treated with colchicine. [2] (b) Complete Table 4.1 by stating the term that matches each of the descriptions. Table. 4.1 term description Region of DNA with repeated nucleotide sequences located at the ends of chromosomes Organises microtubules to form the spindle in animal cells Point of attachment between two sister chromatids [3] [Total: 10]

9744 / H2 Biology / 02 10 5 A student crossed a tan-bodied Drosophila fly with a yellow-bodied Drosophila fly, expecting to get an F1 generation of all tan-bodied flies. Body colour for Drosophila flies are sex-linked. The tan-body allele (T) is known to be dominant over the yellow-body (t) allele. In Drosophila, the males are the heterogametic sex, possessing two different sex chromosomes, X and Y. The results from the cross are shown in Table 5.1. Table 5.1 Phenotype of fly Number of offspring tan-bodied female 27 tan-bodied male 0 yellow-bodied female 0 yellow-bodied male 23 (a) (i) With reference to Table 5.1, describe crosses that can be carried out to determine if body colour is autosomal or sex-linked. [3]