YIJC 2023 H2 9744 P2 ANS

1 @YIJC 9744/02/PE/2022 [Turn over YISHUN INNOVA JUNIOR COLLEGE JC2 PRELIMINARY EXAM Higher 2 NAME INDEX NO CG BIOLOGY Paper 2 Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 9744/02 30 Aug 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name, index no. and CG on this cover page. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions 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 At the end of the examination, submit booklets A, B and C separately to the invigilator. This document consists of 29 printed pages and 1 blank page. For Examiner’s Use Section A 1 10 2 10 3 8 4 10 5 10 6 12 7 10 8 10 9 10 10 5 11 5 Total 100 ANSWERS

2 @YIJC 9744/02/PE/2022 [Turn over Answer all questions 1 Fig. 1.1 shows an electron micrograph of a chloroplast. Fig. 1.1 (a) (i) On Fig. 1.1, use the letter X and a label line to identify where the light independent stage of photosynthesis occurs. Label stroma [1] (ii) Describe two ways in which the structure of the chloroplast is adapted for its function. 1 (fluid-filled matrix called) stroma contains reactants/substrates and enzymes required for Calvin cycle/ light independent reactions; 2 highly folded thylakoid membrane increase SA for embedding of photosynthetic pigments/ light harvesting complexes/ electron carriers of ETC/ ATP synthase for increased rate of light dependent reactions/ chemiosmosis/ photophosphorylation; 3 thylakoid membrane impermeable to H+ allow proton gradient to be set up across thylakoid membrane/ accumulation of H + in thylakoid space; [2] (iii) Chloroplasts and mitochondria both have double membranes. State two other structural similarities between chloroplast and mitochondria. 1 70S ribosomes; 2 Circular DNA; 3 Presence of ETC/ ATP synthase/ stalked particles/ proton pump on membranes; [2]

3 @YIJC 9744/02/PE/2022 [Turn over (b) Fig. 1.2 shows the relationship between CO 2 assimilation rate and increasing light intensity in a plant, when carbon dioxide concentration is not a limiting factor. Fig. 1.2 (i) Explain why the CO2 assimilation rate plateaus at high light intensity. 1 light saturation point has been reached at this point, maximum rate of chlorophyll a photoactivation is occurring (at both photosystems); 2 this means that maximum rate of production of ATP and NADPH is occurring therefore, maximum CO2 assimilation rate is attained in Calvin cycle; 3 at higher light intensities, light intensity is no longer a limiting factor (as further increase in light intensity does not increase rate of photosynthesis) other factors are now limiting e.g. temperature; [3] (ii) Describe what is occurring at point A. 1 A is the compensation point which is the light intensity at which respiration rate = photosynthetic rate; 2 products of photosynthesis (glucose & O2) are used up for cellular respiration while products of (aerobic) respiration (water & CO2) are used up for photosynthesis; 3 No net gain in dry mass thus no growth of plant; [2] MP1 and 2 or 3 [Total: 10]

4 @YIJC 9744/02/PE/2022 [Turn over 2 An investigation was carried out to find the optimum pH and the optimum temperature of an amylase obtained from the bacterium Anoxybacillus thermarum. Fig. 2.1 shows the results of the investigation. Fig. 2.1 (a) With reference to Fig. 2.1, c ompare the effect of temperature on the activity of the amylase and the effect of pH on the activity of the amylase. Similarities: 1 percentage activity reaches maximum at 100 for both optimum temperature at 70oC and pH6.8 – 10.4; 2 percentage activity is lower at lower (below optimum) & higher pH (above optimum) and lower (below optimum) and higher temperature (above optimum); Differences: 3 maximum percentage activity at 100 occurs at a range of pH (4.8 – 10.4) while maximum percentage activity occurs at a single temperature of 70oC; 4 gradual increase of percentage activity from 20 – 100 over a longer range of temperatures (38 – 70oC) compared to sharp increase over a narrower pH range (4.0 – 6.8) 5 gradual decrease of percentage activity from 100 to 62 after range of optimum pH vs sharp decline of percentage activity from 100 to 68 after optimum temperature. [3] (b) Explain the percentage activity of amylase at X. 1 percentage activity declined sharply from 100 at pH 10.4 to 60 at pH 12 beyond range of optimum pH 7 to 10.4, solution/environment of the enzymes has increased OH- concentration/ decreased H+concentration 2 Disrupts (intramolecular) ionic bonds and hydrogen bonds between R groups of amino acids which stabilizes secondary & tertiary structures of enzyme 3 enzyme unfolds and loses its specific 3D conformation, active site is no longer complementary to the substrate, X

5 @YIJC 9744/02/PE/2022 [Turn over Amylase/ enzyme is unable to form ES complex and rate of reaction decreases, amylase/ enzyme is said to be denatured [3] Table 2.1 shows the optimum pH and optimum temperature for amylase from different species of bacteria. Table 2.1 (b) (i) Using the data in Fig. 2.1 and Table 2.1, identify the bacterial species that has amylase most similar to amylase from Anoxybacillus thermarum. Bacillus amyloliquefaciens; [1] (ii) Suggest why the amylase molecules of some species of bacteria are able to work at higher temperatures than others. 1 due to presence of more disulfide bridges which are strong covalent bonds; 2 formed between sulfhydryl/ SH R groups of cysteine amino acids within polypeptide chain; 3 higher temperatures, higher energy required to break disulfide bridges to lose its 3D configuration shape; [3] [Total: 10]

6 @YIJC 9744/02/PE/2022 [Turn over 3 (a) Stem cells from the human bone marrow that are involved in blood cell formation are described as multipotent, rather than totipotent. Compare multipotent and totipotent stem cells. Similarity – any 1 1 Both are undifferentiated, thus capable of differentiating into specialized cells; 2 Both do not possess any specialized-cell structures, hence are unspecialized; 3 Both u ndergo asymmetrical division in which one daughter cell is identical to parent cell while the other is a progenitor cell (which proceeds to further differentiate); owtte 4 Both are capable of long-term self-renewal/indefinite replication due to expression of active telomerase; Difference – any 1 Totipotent Multipotent 4 Found in zygote Found in developed tissues / organs; 5 Able to differentiate into all cell types to form whole organism Able to differentiate into a limited range of the same lineage; [2] ER: Many students appeared to misunderstand the command term "compare" which necessitates highlighting both similarities and differences. A significant portion of the responses provided only differences. It was evident that a considerable number of students had not adequately revised this topic, particularly evident in the explanat ions provided about the potency of the stem cells. Several students offered partially complete definitions of stem cell potency, wh