2024 VJC H2 Bio P3 QP

1 VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION 2024 HIGHER 2 NAME : ……………………………………………………….………………. CT CLASS: ………………..……… BIOLOGY Paper 3 Long Structured and Free-response Questions 9744 / 03 17/09/2024 2 hour Candidates answer on the Question Paper. No Additional Materials are required. 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 any one question in the space 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 bracket [ ] at the end of each question or part question. Question Marks Section A 1 2 3 Section B Total This document consists of 24 printed pages. [Turn over]

2 Section A Answer all the questions in this section. 1 Thyroid hormones are produced and released by the thyroid gland. In humans, the thyroid gland is found in the neck below the Adam’s apple. It is lined with thyroid follicular cells, also called thyrocytes, that surround a lumen. Fig. 1.1 shows the thyroid follicular cells. Fig. 1.1 Unlike most hormones with specific target cells or tissues, the thyroid hormones act on nearly every cell in the body and are important in regulating the basal metabolic rate of the body. They regulate the metabolism of proteins, fat and carbohydrates in cells, affecting protein synthesis and cellular respiration. They are also involved in the control of heat generation in the body and are essential for proper cell development and differentiation. There are two types of thyroid hormones, namely triiodothyronine (T3) and thyroxine (T4). Their structures differ by the number of iodine present. Fig. 1.2 shows the structure of T3 and T4. Fig. 1.2

3 (a) With reference to Fig. 1.1 and 1.2, (i) suggest how thyroid hormones are able to act on nearly every cell in the body. …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [1] (ii) compare the structure of thyroid hormones to an amino acid. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [2] (b) The release of thyroid hormones from the thyroid gland is regulated by other hormones released from the brain. Neurones in the hypothalamus in the brain release thyrotropin - releasing hormone (TRH), which stimulates the release of thyroid -stimulating hormone (TSH) from cells in the anterior pituitary. TSH then stimulates the release of T3 and T4 from the thyroid gland. Fig. 1.3 shows the relationship between different tissues in the control of the release of thyroid hormones. Fig. 1.3

4 Research was conducted to study the effect of TSH on the release of thyroid hormones from the thyroid gland. In this research, pluripotent stem cells were induced to differentiate into a culture of thyroid follicular cells. TSH was then introduced into the culture medium of this cell culture, and the amount of T 3 and T 4 released into the culture medium was measured for a period of one week. The result of this experiment is shown in Fig. 1.4. Fig. 1.4 With reference to Fig. 1.4, (i) compare the changes in the levels of T3 and T4 in the cell culture medium during the week. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [2] (ii) contrast the release of thyroid hormones with the release of antibodies. …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [1]

5 Question 1 continues to page 6.

6 (c) The research continued and managed to discover the signalling pathways involved in the stimulation of the thyroid gland by TSH. The action of TSH on the thyroid follicular cells in the thyroid gland is shown in Fig. 1.5. Fig. 1.5 (i) Identify the proteins labelled A and B. A ………………………………………………………………………………………………... B …………………………………………………………………………………………..… [2] (ii) Explain the significance of protein A in TSH signalling. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [3]

7 (iii) Ca2+ ions are released from an organelle in the thyroid follicular cell when the cell is stimulated by TSH. Describe how the structure of this organelle allows its roles in TSH signalling. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [3]

8 (d) Beside the action of TRH and TSH, another regulatory mechanism of thyroid hormones is via the supply of iodine, an important component of thyroid hormones. Most dietary iodine is reduced to iodide ions before absorption by the small intestine. The iodide ions are transported to the thyroid gland via the circulatory system and accumulated in thyroid follicular cells. Fig. 1.6 shows the uptake of iodide ions by a thyroid follicular cell. Fig. 1.6 With reference to Fig. 1.6 and your knowledge on transport across membrane, (i) calculate the number of ATP required in the uptake of 10 mol of iodide ions into the thyroid follicular cell. Leave your answer to 3 significant figures. Show your working in the space provided. number of ATP required = …………… mol [1]

9 (ii) explain the need for transport proteins in the uptake of iodide ions into the thyroid follicular cell. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [4] (iii) state two differences between the transport of iodide ions and thyroglobulin into the lumen of the thyroid gland. feature of comparison transport of iodide ions into thyroid gland lumen transport of thyroglobulin into thyroid gland lumen [2]

10 (e) Thyroid hormones, unlike most protein hormones, are transported into target cells and bind to intracellular receptors known as thyroid hormone receptors (TRs). TRs often form heterodimers with retinoic X receptor (RXR) and act as a transcription factor for a wide variety of genes. The dimer binds to a thyroid hormone response element (TRE) on the DNA and recruits co-repressors to repress gene expression. Fig. 1.7 shows the action of thyroid hormone in the target cell. Fig. 1.7 (i) Briefly outline how T4 is converted to T3 in the cytoplasm. …………………………………………………………………………………………………... …………………………………………………………………………………………..…… [1]