RVHS 2023 JC2 H2 Prelim P3 QP

1 RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CENTRE NUMBER S CLASS 22J INDEX NUMBER BIOLOGY 9744/03 Paper 3 Long Structured and Free-response Questions 15 September 2023 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name 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. DO NOT WRITE ON ANY BARCODES. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer any one question 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 not use appropriate units. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 2 3 Section B Total This document consists of 26 printed pages and 2 blank pages.

2 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Section A Answer all the questions in this section. 1 The gut microbiota is the community of all micro-organisms (bacteria, archaea, protozoa, fungi, and viruses) present in the digestive tract. Bacteria are the largest component of the microbiota. (a) Describe the structure of bacterial genome. [3]

3 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Question 1 continues on page 4

4 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Gut bacteria are present in a range of species in Kingdom Animalia including insects, fish, and apes. Gut bacteria are passed vertically from mother to offspring. Its composition and abundance have changed in the generations with evolutionary time. Fig. 1.1 shows the relative change in abundance of selected bacterial taxa in the evolution of humans (Homo sapiens). Relative change is shown by the “_x” in the box beside the descendant species, for example “5x” refers to a five times increase in abundance from the ancestor. Adapted from Moeller et al, PNAS, 111(46), 2014 Fig. 1.1 (b) With reference to the animals in Fig. 1.1, explain how phylogeny is related to classification. [2]

5 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Diet has a significant influence on gut bacteria composition. Different diets contribute different nutrients to the digestive tract which affects the presence and proportion of various bacterial genera. Chimpanzees’ (genus: Pan ) diet mainly comprise of plants and plants’ produce, with meat contributing only 2% of their diet. Table 1.1 sho ws how different nutrients affect selected bacterial genera. Table 1.1 Adapted from Tomova et al, Frontiers in Nutrition, 6(47), 2019 (c) Using your knowledge and information from Fig. 1.1 and Table 1.1, (i) predict the change in proportion for Bacteroides and Fibrobacter in the gut of Homo sapiens and fill in the boxes in Fig. 1.1 with their genus names, and [2] (ii) comment on the validity of the statement “gut bacteria can act as evidence of evolution”. [4] key + nutrient causes an increase in abundance of bacteria – nutrient causes a decrease in abundance of bacteria shaded boxes mean that information is unknown

6 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Horizontal gene transfers (HGT) occur frequently in gut bacteria, particularly in response to selection pressures targeting new functions such as antibiotic resistance. Fig. 1.2 shows the HGT rate of antibiotic resistance genes across taxonomic levels of bacteria, and two sets of data, the HGT rate within an individual’s gut and the HGT rate between two individuals’ gut. Adapted from Kent et al, Nature Communications, 2020 Fig. 1.2 (d) (i) Outline how antibiotic resistance genes are transferred between bacteria. [3]

7 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination (ii) Account for one similarity and one difference in the two data sets in Fig. 1.2. [4]

8 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination Gut bacteria provide essential health benefits to their hosts. These include nutrient metabolism, drug metabolism and regulating immune homeostasis. Gut bacteria have a role in innate immunity, and more importantly can also induce T lymphocyte differentiation. Details of how gut bacteria induces T lymphocyte differentiation are provided below: • Naïve CD4+ T cells can differentiate into four major T cell subtypes: Th1, Th2, Th17 and regulatory T cell (Treg). • Differentiation into subtypes Th1 and Treg can be triggered by gut bacteria. • Bacteroides and Clostridium secrete Polysaccharide A (PSA) and indole metabolite respectively, which bind different receptors on the naïve CD4+ T cell. • This induces different transcription factors resulting in differentiation into the 4 lineages. Uncontrolled Th1 and Treg responses result in gastrointestinal -associated autoimmune diseases while uncontrolled Th2 responses result in allergic reactions. Fig. 1.3 shows the interactions of gut bacteria, Bacteroides and Clostridium, on naïve CD4+ T cells and its differentiated T cell subtypes. Adapted from Wu et al, Gut Microbes, 4(14), 2012 Fig. 1.3

9 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination (e) Using information provided in this entire question, deduce the outcomes on an individual with a gain-in -function mutation of the promoter of the TLR2 receptor gene, and living in a country of high affluence. [5] (f) State the advantage of cell signalling shown in Fig. 1.3. [1] (g) Scientists identified Mg 2+ ion as a possible second messenger involved in T lymphocyte activation. Describe the nature of second messengers such as Mg2+. [1] [Total: 25]

10 River Valley High School H2 Biology 9744/03 2023 JC2 Preliminary Examination 2 Apoptosis is an important part of tissue homeostasis. It ensures that cells die quickly and are safely removed when necessary. (a) Protein kinases play an important role in the cell signalling pathway leading to apoptosis. Explain the role of protein kinases. [2] (b) The BCL-2 protein is involved in the regulation of apoptosis. It is a monomeric protein consisting of a single polypeptide chain. Outline how BCL-2 protein is synthesised from its mRNA. [5]