2024 NJC H2 Bio P4 QP

© NJC 20249744/04/SH2 Preliminary Examination[Turn over H NATIONAL JUNIOR COLLEGE, SINGAPORE Senior High 2 Preliminary Examination Higher 2 CANDIDATE NAME BIOLOGY CLASS 2bi2_____ REGISTRATION NUMBER Biology Paper 4 Practical 9744/04 26 August 2024 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name, Biology class, and registration number on all the work you hand in. Give details of the practical shift and laboratory in the boxes provided. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs. 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 workings or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part of question. Shift 1 2 3 Laboratory BI23 BI24 CM42 CM43 CM44 For Examiner’s Use 1 17 2 22 3 16

2 © NJC 20249744/04/SH2 Preliminary Examination Total 55 This document consists of 20 printed pages.

3 © NJC 20249744/04/SH2 Preliminary Examination[Turn over Answer all questions. 1 Yeast can convert different respiratory substrates into carbon dioxide via cellular respiration. You will investigate the effect of different respiratory substr ates on the rate of respiration in yeast. Hydrogencarbonate indicator is a pH indicator which can be used to measure the amount of carbon dioxide produced by the respiring yeast cells. When carbon dioxide dissolves in water, carbonic acid is formed, reducing the pH and changing the colour of the indicator solution. The initial pH of the reaction mixture containing yeast and respiratory substrate may be slightly different depending on the type of respiratory substrate. This can be standardised by using sodium bicarbonate solution to adjust pH so that the starting c olour corresponds to the colour number 6 on the hydrogencarbonate indicator colour chart provided. You are provided with: ● yeast suspension, labelled Y ● alginate solution, labelled A ● calcium chloride solution, labelled C ● respiratory substrate 1, labelled S1 ● respiratory substrate 2, labelled S2 ● respiratory substrate 3, labelled S3 ● hydrogencarbonate indicator, labelled H ● sodium bicarbonate solution, labelled B ● distilled water ● hydrogencarbonate indicator colour chart Read steps 1–12 before starting the investigation. Proceed as follows. 1 Add about 30cm3 of C into a 50cm3 beaker. 2 Stir Y to suspend the yeast cells. Transfer 3.0cm3 of Y into another 50cm3 beaker. 3 Add 6.0cm3 of A into the beaker containing Y, taking care not to introduce air bubbles into the mixture. Stir the resulting yeast-alginate mixture gently using a glass rod. Do not mix vigorously as this may introduce air bubbles into the mixture. 4 Remove the plunger of a 5.0cm 3 syringe. Hold the empty syringe barrel with the nozzle facing down above the beaker containing C as shown in Fig. 1.1. 5 Pour the yeast-alginate mixture prepared from step 4 into the syringe barrel and allow the yeast-alginate mixture to drip into C as shown in Fig. 1.1. As it drips, gently swirl the beaker to prevent the beads from aggregating with each other. The mixture will form a bead upon contact with calcium chloride.

4 © NJC 20249744/04/SH2 Preliminary Examination Fig. 1.1 6 Transfer only the yeast-alginate beads into a Petri dish. Rinse the beads with distilled water. Keep the yeast-alginate beads in distilled water. Remove and discard any bead that is obviously different in size, distorted in shape, or floating. You will need to use 15 yeast-alginate beads for Question 1. Keep 25 yeast-alginate beads for Question 2. 7 Add 2.0cm3 of S1 and 0.2cm3 of H into a test tube. Mix the tube contents well. 8 Check if the colour of the mixt ure matches colour 6 on the hydr ogencarbonate indicator colour chart. If not, using a 1cm 3 Pasteur pipette, add B dropwise to the mixture until colour 6 is achieved. 9 Add five yeast-alginate beads into the test tube. You should en sure that as little distilled water is transferred along with the beads as possible. Start timing immediately. 10 At the end of three minutes, mix the tube contents well. 11 Record, in (a)(i), the final colour of the mixture, using the colour number whic h it matches with on the hydrogencarbonate indicator colour chart. 12 Repeat steps 7–11 with each of the other respiratory substrates, S2 and S3.

5 © NJC 20249744/04/SH2 Preliminary Examination[Turn over (a) (i) Record your results in an appropriate table. [3] (ii) All three respiratory substrates, S1, S2 and S3, are carbohydrates but only one of them is a polysaccharide. Based on your results obtained in (a)(i), put a tick ( ✓) in the appropriate box to indicate the respiratory substrate that is a polysaccharide and explain your answer. S 1 S 2 S 3 explanation [3]

6 © NJC 20249744/04/SH2 Preliminary Examination (iii) Describe a suitable control for this investigation and explain its purpose. control purpose [2] ( i v ) Identify one significant source of error in this investigation and suggest an improvement to the procedure that will reduce the effect of the error. error improvement [2]

7 © NJC 20249744/04/SH2 Preliminary Examination[Turn over (b) Microalgae synthesise various carbohydrates to support cellular functions. Cellulose and starch are the most abundant polysaccharides found in microalgae. However, microalgae have also been reported to synthesise two novel carbohydrates, N1 and N2. A student carried out an investigation with N1 and N2 to find out their effect on the rate of respiration in yeast. Methylene blue was used to monitor the rate of respiration. It acts as an artificial hydrogen acceptor. When this dye is reduced by accepting hydrogen atoms it turns from blue to colourless. Table 1.1 shows the results of the investigation. Table 1.1 sample number time taken for decolourisation of methylene blue / s N1 N2 1 181 190 2 182 191 3 190 192 4 178 193 5 184 194 6 183 194 7 181 196 8 179 197 9 190 190 10 179 192 mean (𝑥) 182.7 192.9 standard deviation (𝑠) 4.27 2.38 variance (𝑠ଶ) ( i ) Complete Table 1.1 by calculating the variance ( 𝑠ଶ) for the time taken for decolourisation of methylene blue in the presence of each of th e carbohydrates: N1 and N2. [1]

8 © NJC 20249744/04/SH2 Preliminary Examination (ii) A t-test can be used to determine whether there is any significant difference between the time taken for decolourisation of methylene blue in the presence of N1 and N2. Calculate the value of t and the number of degrees of freedom, using these formulae: 𝑡 ൌ |𝑥ଵ െ𝑥 ଶ| ඨ൬ 𝑠ଵ ଶ 𝑛ଵ ൅ 𝑠ଶ ଶ 𝑛ଶ ൰ 𝑣 ൌ 𝑛ଵ ൅𝑛 ଶ െ2 Show your working. value of t = number of degrees of freedom = [2] (iii) State the null hypothesis. [1]

9 © NJC 20249744/04/SH2 Preliminary Examination[Turn over Table 1.2 shows the critical values for t at several different probabilities and degrees of freedom. Table 1.2 degrees of freedom probability, p 0.5 0.1 0.05 0.01 1 1.00 6.31 12.71 63.66 2 0.82 2.92 4.30 9.92 3 0.76 2.35 3.18 5.84 4 0.74 2.13 2.78 4.60 5 0.73 2.02 2.57 4.03 6 0.72 1.94 2.45 3.71 7 0.71 1.89 2.36 3.50 8 0.71 1.86 2.31 3.36 9 0.70 1.83 2.26 3.25 10 0.70 1.81 2.23 3.17 11 0.70 1.80 2.20 3.11 12 0.70 1.78 2.18 3.05 13 0.69 1.77 2.16 3.01 14 0.69 1.76 2.14 2.98 15 0.69 1.75 2.13 2.95 16 0.69 1.75 2.12 2.92