MI 2023 J2 H2 BI Prelim P3 ANS

Class Adm No Candidate Name: ___________________________________ This question paper consists of 21 printed pages, including 1 blank page. [Turn over] 2023 End-of-Year Examination Pre-University 3 H2 Biology 9744/03 Paper 3 Long Structured and Free-response Questions 20 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your Admission number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, 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 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 Question Marks A 1 /30 2 /10 3 /10 B 4/5 /25 Total Marks /75

2 9744/03/PU3 EOY/2023 Section A Answer all questions in this section. 1 The tomato plant (Solanum lycopersicum) is a crop harvested in many regions of the world for its edible fruit. Its red skin is primarily due to the presence of the organic compound lycopene, a pigment also found in many other fruits such as carrots and watermelon. Lycopene is only made up of carbon and hydrogen, as shown in Fig. 1.1. Lycopene is also a precursor to many carotenoids, which absorb light from a certain wavelength during photosynthesis. In addition to carotenoids, other essential pigments are chlorophylls a and b. Fig. 1.1 (a) (i) Suggest a cellular structure in which lycopene can be found in a tomato cell. Explain your answer. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...……………………………………... [2] 1. Cell surface membrane/mitochondrial membrane/membrane of endoplasmic reticulum/membrane of Golgi apparatus; 2. Carbon and hydrogen in lycopene allow favourable hydrophobic interaction with hydrophobic fatty acid tail /hydrophobic core of lipoproteins

3 9744/03/PU3 EOY/2023 [Turn over] Fig. 1.2 shows the absorption spectrum of lycopene and the action spectrum of the tomato plant. Fig. 1.2 (ii) With reference to Fig. 1.2, state the wavelength(s) of peak absorption by lycopene. ………………………………………………...……………………………………... [1] (iii) Explain how the data in Fig. 1.2 shows that lycopene is not the only photosynthesis pigment in the tomato plant. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...……………………………………... [2] 500 nm, 460nm 1. Lycopene does not absorb light above 550/560nm; 2. But photosynthesis still takes place above 550/560nm according to the action spectrum; Action spectrum Absorption spectrum of lycopene

4 9744/03/PU3 EOY/2023 (b) Different conditions and variables can greatly affect the rate of photosynthesis that occurs in tomato plants. To investigate this, the net photosynthetic rate (P N) was measured against photosynthetically active radiation (PAR) . PAR measures the amount of photons that the plant is exposed to per unit area per unit time. The plants were also subjected to four different levels of relative soil water content (RSMC), labelled T1 to T4. (RSMC) measures the amount of water in the soil. Fig. 1.3 shows the results. Fig. 1.3 PN (µmol m-2s-1) PAR (µmol m-2s-1) T1 T2 T3 T4

5 9744/03/PU3 EOY/2023 [Turn over] (i) Explain the overall relationship between PN and RSMC from 0 to 1000 µmol m- 2s-1. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...……………………………………... [3] (ii) Suggest and explain the overall trend observed from 1500 to 2000 µmol m-2s-1. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...…………………………………………. ………………………………………………...……………………………………... [2] (iii) Using Fig. 1.3, estimate the PN when the PAR is 750 µmol m-2s-1 and the RSMC is between 55% to 61%. ………………………………………………...……………………………………... [1] 1. As RSMC increases from T4, to T1, the highest PN value increases from 5.8 µmol m-2s-1 to 7.8 µmol m-2s-1; 2. Higher RSMC means there is a higher water content, which also means there is a higher rate of photolysis of water; 3. Allows for more electrons to be passed down the electron transport chain during light dependent reaction, increasing production of ATP and NADPH; 4. ATP and NADPH used for Calvin Cycle to form G3P, thus increasing the rate of photosynthesis; 1. The PN of all curves gradually decreases from 1500 to 2000 µmol m-2s-1; 2. PAR/light intensity is no longer a limiting factor; 3. Rate of photosynthesis decrease due to heat stress; 6.5-6.8 µmol m-2s-1

6 9744/03/PU3 EOY/2023 (c) The products of the light -dependent reaction are important for the formation of carbohydrates in plants. Outline how carbohydrate can be continually formed using these products. ……………………………………….……………...…………………………………………. ……………………………………………………....…………………………………………. ……………………………………….……………...…………………………………………. ……………………………………………………....…………………………………………. ……………………………………….……………...…………………………………………. ……………………………………….……………...…………………………………………. ……………………………………………………....…………………………………………. ………………………………………………..……...……………………………………... [4] 1. Carbon dioxide reacts with RuBP, cataysed by Rubisco to eventually form PGA; 2. ATP and NADPH reduce PGA to form G3P; 3. For every 3 molecules of CO2, there are 6 molecules of G3P; 4. One molecule of G3P exits the cycle to be used as carbohydrate; 5. the other 5 molecules form RuBP using ATP/RuBP is regenerated and can continue to fix carbon dioxide; Any 4 points for 4 marks;

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8 9744/03/PU3 EOY/2023 Stressful conditions can lead to the damaging of plant DNA. This leads to the activation of multiple cell signalling pathways to repair the DNA, which involves halting the cell cycle at its checkpoints. Fig. 1.4 shows one such simplified pathway, known as the DNA damage response (DDR) signalling pathway. DDR activation depends on two protein kinases, ATM and ATR. ATM responds to double-stranded breaks (DSBs), where a double-stranded DNA breaks off at both strands, and ATR is activated by the presence of single-stranded DNA and any defects in replication fork progression. The result of the pathway is the inhibition of cell cycle progression. In response to the activation of ATM and/or ATR, the following pathways occur: • Phosphorylation of the histone protein H2AX to form γ-H2AX (gamma-H2AX). • The activation of SOG1, a transcription factor, activating proteins NAC44 and NAC85, which in turn will lead to the regulation of the M checkpoint. • The expression of RBR1 and E2FA proteins, which are tumour suppressor proteins and WEE1, which is a G2 Checkpoint Kinase. Through the activation of DDR, the DNA is subsequently repaired. Fig. 1.4

9 9744/03/PU3 EOY/2023 [Turn over] Table 1.1 lists down three processes that will result from the activation of the DDR pathway. Table 1.1 Which protein kinase ATM and/or ATR will be activated? Protein(s) involved Processes due to activation of ATM / ATR formation of het