2024 ACJC H2 Bio P3 QP

This document consists of 17 printed pages. [Turn over Anglo-Chinese Junior College JC2 Biology Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS I N D E X NUMBER BIOLOGY Paper 3 Long Structured and Free-response Questions Additional Materials: Free-response Question Answer Booklet 9744/03 28 August 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your Name, Class and Index number 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 q u e s t i o n i n t h e s p a c e s p r o v i d e d o n t h e s e p a r a t e F r e e - r e s p o n s e Question Answer Booklet. 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 Examiners’ use only 1 / 30 2 / 10 3 / 10 4 / 5 / 25 Total / 7 5

2 Anglo-Chinese Junior College 2024 J2 H2 9744 Paper 3 Preliminary Examination For Examiner Use Section A Answer all the questions in this section. 1 Lactose is the main carbohydrate found in mammalian milk and is i m p o r t a n t f o r m e e t i n g t h e nutritional needs of an infant. Lactose is a disaccharide of glucose and galactose, and has been considered healthier than other disaccharides such as sucrose and maltose. Table 1.1 shows the glycaemic index of lactose, sucrose, maltose and glucose. The glycaemic index measures the rise in blood glucose levels two hours after i n g e s t i o n o f t h e m e a s u r e d substance. Table 1.1 carbohydrate glycaemic index lactose 46 sucrose 65 maltose 105 glucose 100 (a) Suggest explanations for the following two observations: ( i ) the glycaemic index of lactose is lower than glucose ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. …………………………………………………………………………………………............ [1] ( i i ) the glycaemic index of lactose is lower than sucrose. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………............ [2]

3 [Turn over Anglo-Chinese Junior College 2024 J2 H2 9744 Paper 3 Preliminary Examination For Examiner Use Lactose intolerance is a condition which occurs due to the lack of the enzyme lactase in the small intestines. In humans, lactase is encoded by the LCT gene on chromosome 2. In most of the human population, lactose intolerance occurs as the expression of the LCT gene declines past the infant stage due to a reduced reliance on milk. Adults with lactose intolerance will present with gastrointestinal symptoms when milk is consumed, and the condition worsens with age. It is hypothesised that methylation of the promoter of the LCT gene is involved in the age-related decrease in gene expression. ( b ) Explain how methylation of the promoter may lead to a decrease in LCT gene expression. ……………………………………………….………………………………………………………….. ……………………………………………….………………………………………………………….. ……………………………………………….………………………………………………………….. ……………………………………………….………………………………………………………….. ……………………………………………….………………………………………………………….. ……………………………………………….………………………………………………………….. ……………………………………………………………………………………………………….. [3]

4 Anglo-Chinese Junior College 2024 J2 H2 9744 Paper 3 Preliminary Examination For Examiner Use The extent of methylation of the LCT gene was analysed in 48 individuals between the ages of 8 to 23 and of a largely European descent. Fig. 1.1 records the percentage methylation of the LCT gene and the lactase activity measured in each individual. Fig. 1.1 (c) (i) Draw a line of best fit on Fig. 1.1. [1] ( i i ) Discuss whether the results in Fig. 1.1 support the hypothesis that methylation is involved in the age-related decline in LCT gene expression. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………............ [4] 0 10 20 30 40 50 60 70 80 70 75 80 85 90 95 100 lactase activity / arbitrary units percentage methylation

5 [Turn over Anglo-Chinese Junior College 2024 J2 H2 9744 Paper 3 Preliminary Examination For Examiner Use In some individuals, LCT gene expression continues throughout adulthood, allowing the digestion of lactose in milk. These adult individuals are said to be lactase persistent and can tolerate the consumption of milk. Genomic studies have identified the MCM6 gene to be involved in the regulation of the expression of the LCT gene. Scientists made these observations of the two genes, represented in Fig. 1.2:  MCM6 gene is located upstream of the LCT gene on the same chromosome  MCM6 gene contains 15 introns  m u t a t i o n s i n s p e c i f i c D N A s e q u e n c e s w i t h i n t w o o f t h e i n t r o n s have been found in individuals who are lactase persistent  r e g u l a t o r y p r o t e i n s c a n b i n d t o t h e s e s p e c i f i c D N A s e q u e n c e s that have undergone mutations  t h e s e r e g u l a t o r y p r o t e i n s c o n trol the transcription of the LCT gene. Fig. 1.2 (d) (i) Suggest how mutations to specific DNA sequences in the introns of the MCM6 gene may result in the lactase persistent condition. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. …………………………………………………………………………………………............ [4]

6 Anglo-Chinese Junior College 2024 J2 H2 9744 Paper 3 Preliminary Examination For Examiner Use ( i i ) Describe one other mechanism by which introns may play a role in the regulation of gene expression. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. ………………………………………….…………………………………………………………. …………………………………………………………………………………………............ [2] Lactose in milk cannot be directly absorbed at the small intestines. It needs to be hydrolysed by intestinal enzymes before the resulting monosaccharides can be taken up. When a person with lactose intolerance consumes milk, the unhydrolysed lactose passes into the large intestines, where it is metabolised by bacteria in the large intestines using a mechanism similar to that in yeast under low oxygen conditions. Gas produced through bacteria metabolism of lactose results in bloating and abdominal discomfort. Other metabolic products and any unabsorbed sugars in the lumen