VJC 2021 H2 Bio 9744 P3 QP

1 VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2021 HIGHER 2 NAME : ……………………………………………………….………………. CT CLASS: ………………..……… BIOLOGY Paper 3 Long Structured and Free-response Questions 9744/03 22/09/2021 2 hour Candidates answer on the Question Paper. Additional Materials: Answer Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT class in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer one question. Write your answer in the Answer Booklet provided. 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 not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in bracket [ ] at the end of each question or part question. Question Marks Section A 1 2 3 Section B 4 or 5 Total This document consists of 16 printed pages. [Turn over]

2 Section A starts on page 3

3 Section A Answer all questions. 1 Drosophila are small flies in the order Diptera and family Drosophilidae. Commonly known as fruit or vinegar flies, they are often found on rotting fruit or other decaying matter. They are one of the most valuable organisms in biological research, particularly in genetics and developmental biology. The genome of Drosophila melanogaster comprised of eight chromosomes ( 2n=8), of which two of them are sex chromosomes. Like humans, the male is the heterogametic sex. Fig. 1.1 shows the chromosomes present in a male Drosophila. Fig 1.1 (a) (i) Circle the sex chromosomes in Fig. 1.1. [1] (ii) Explain what is meant by “heterogametic sex”. ……………………………………………………………………………………………….……... ………………………………………………………………………………………………….…... ……………………………………………………………………………………………….……... ………………………………………………………………………………………………….. [2]

4 Chromosomes contain the units of inheritance and their behavior during meiosis can be used to explain Mendel’s laws of inheritance. (b) Explain how the behavior of chromosomes during meiosis supports Mendel’s law of segregation and independent assortment. Law of segregation: ………………………………………………………………………..…………………………….. …………………………………………………………………………………..………………….. ………………………………………………………………………………………..…………….. ………………………………………………………………………………………..……….. [2] Law of independent assortment: ………………………………………………………………………………………………….…... ………………………………………………………………………………………………….…... ……………………………………………………………………………………………….……... ………………………………………………………………………………………………….. [2] Researchers studying the development of embryo in Drosophila noted the presence of mRNA coding for four different proteins: bicoid, caudal, hunchback and nanos, present in the cytoplasm of the oocyte (unfertilised egg). Before fertilisation, these maternal mRNA are not translated. Initiation of translation occurs only upon fertilisation. (c) Describe one way in which translation of the maternal mRNA in the egg can be prevented. …………………………………………………………………………………………….………... ……………………………………………………….……………………………………………... …………………………………………………………….………………………………………... ………………………………………………………………………………………………….. [2]

5 Fig. 1.2 shows the development of the embryo upon fertilisation. Fig. 1.2 https://www.researchgate.net/figure/Early-stages-of-embryonic-development-in-Drosophila_fig11_310995415 (d)(i) Suggest an advantage of nuclei of the early embryo sharing a common cytoplasm. ………………………………………………………………….…………………………………... ………………………………………………………………………………………………….. [1] (ii) Cellularisation occurs when c ell membranes are formed around each nucleus to form cells. Explain the importance of cellularisation in the continued development of the embryo. …………………………………………………………………………….………………………... …………………………………….………………………………………………………………... ……………………………………….……………………………………………………………... ………………………………………………………………………………………………….. [2]

6 The maternal mRNA and their respective proteins can be found in the common cytoplasm of the embryo. Fig 1.3 shows the concentration and distribution of the four maternal mRNA in the common cytoplasm of the fertilised egg. These mRNA are anchored to cytoskeleton present within the cytoplasm. The distribution of the four proteins is important in the determination of the anterior - posterior (head-tail) axis of the embryo. Fig 1.4 shows the distribution and concentration of these proteins. Fig. 1.3 Fig. 1.4

7 (e) Using the information from Fig. 1.3 and 1.4, (i) account for the distribution of bicoid and nanos proteins. …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... ………………………………………………………………………………………………….. [2] (ii) suggest explanations for the distribution of the hunchback and caudal proteins. …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... ………………………………………………………………………………………………….. [3] The bicoid protein can be transported into the nuclei where it can result in the development of specific structures (eg. head, thorax) in the anterior region of the embryo. (f) Suggest how the bicoid protein can result in the development of specific structures in the anterior region of the embryo. ……………………………………………………………………………….……………………... ……………………………………………………………………………….……………………... ………………………………………………………………………………….…………………... ……………………………………………………………………………….……………………... ……………………………………………………………………………….……………………... ……………………………………………………………………………….……………………... ………………………………………………………………………………………………….. [3]

8 In the salivary gland of the Drosophila larvae, large chromosomes known as polytene chromosomes can be seen during development. During the formation of the polytene chromosome, paired homologous chromosomes undergo repeated divisions to form many chromatids without segregating. The newly formed chromatids remain associated lengthwise and together form a cable -like structure. These giant chromosomes posses s characteristic patterns of alternating dark and light bands, which are readily observed when stained. Fig. 1.5 shows portions of polytene chromosomes that have been stained. Fig 1.5 (g) (i) If each of the DNA has undergone 10 rounds of DNA replication, how many DNA molecules are there in one polytene chromosome? ………………………………………………………………………………………………….. [1] (ii) Explain why it is unusual for homologous chromosomes to pair up in the salivary gland. ……………………………………………………………………………………….……………... ………………………………………………………………………………………………….. [1] (iii) Explain how repeated divisions can result in the banding pattern seen in Fig.1.5. …………………………………………………………………………………….………………... ………………………………………………………………………………….…………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... …………………………………………………………………………………….………………... ………………………………………………………………………………………………….. [3]

9 Scientists have labelled the banded regions of these giant chromosomes and use them to distinguish between different species of Drosophila. (h)(i) Suggest why different species of Drosophila show different banding patterns for the same polytene chromosome. …………………………………………………….………………………………………………... ……………………………………………………….……………………………………………... ……………………………………………………….……