HCI 2023 JC2 Prelim H2 Biology Paper 4 MS (Sharing)

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2023 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 4 MARK SCHEME QUESTION 1 Part A Observe and make brief notes of any differences between a leaf from plant A and a leaf from plant B. leaf from plant A is green whereas leaf from plant B has patches of yellow (a) State two differences between the chloroplasts from specimen A and specimen B. [2] any two: 1 extract A has more chloroplasts 2 extract A has green chloroplasts but extract B has colourless / yellow chloroplasts 3 extract A has more developed chlorophyll than extract B (b) Prepare the space below to record your results in an appropriate format so that you can compare extract A with extract B. Include the R f value for each pigment calculated as instructed in step 21. [4] 1 correct table headings without units 2 table layout that compares colour and Rf in the 2 extracts 3 correct observation of colour of pigments 4 location of pigments (c) Label your chromatograms A and B and paste them in the space below using the sticky tapes provided. [1] distance shown to solvent front and front of at least one pigment (d)(i) Other than lack of replicates, suggest one source of error in this procedure and explain how it affects your results. [2] one mark for each statement of the following pairs: L1 location of the pigment position E1 calculation of Rf value may be inaccurate L2 extract may not have been concentrated enough E2 not certain if all the pigments have been extracted (d)(ii) Suggest an improvement that can be made to eliminate the error. [1] any one: 1 use a longer piece of chromatography paper 2 use more leaves to make the extract

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 2 (e) Plot a graph of the absorbance for the young plants against wavelength of light. [3] 1 scale + correct axis orientation with appropriate labels & units 2 use of different symbols to represent each graph 3 all correct plots (f) From the graph plotted, suggest what conclusions can be made about the number of pigments and about the concentration of pigments in the two sets of young plants. [2] 1 same number of pigments 2 leaf extract from plant A has a higher concentration of pigments (g) Seedlings A and B were grown in different conditions. (i) Based on all your observations and the experimental data available, suggest how the growing conditions were varied. [1] seedling A is grown in light but seedling B is grown in the absence of light (ii) Explain how the results from all your observations and the experimental data support this conclusion. [2] 1 leaf from plant A is green whereas leaf from plant B has patches of yellow 2 leaf extract A has more chloroplasts 3 leaf extract A has more pigments 4 leaf extract from plant A has a higher concentration of pigments

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 3 Part B (h) Design an experiment to compare the rates of complete hydrolysis of PT by EN and EX. [9] Variables: 1 mark IV: type of enzyme DV: rate of complete hydrolysis of protein determined by reciprocal of time taken for complete hydrolysis of protein Scientific reasoning used to decide the method: 1 mark any one: S1 ref. to PT having six hydrolysis sites for EN versus two hydrolysis sites for EX, so EN and EX have different specific 3D conformation of active site, hence products of hydrolysis differ S2 ref. to different products of hydrolysis have different solubil ity in solvent used in chromatography, resulting in different number of spots Method: 4 marks M1 CV control: contents of EN, EX and PT in the respective reaction mixtures M2 CV control: equilibrate protein and enzyme solutions separately M3 CV control: Mix EN / EX with protein + incubate in thermostatically controlled water bath + start stopwatch M4 DV measurement: remove sample of reaction mixture using micropipette tips + at 5 min intervals + use chromatography paper and solvent M5 DV measurement: locate products of hydrolysis on the chromatograms using a spray bottle containing a specific dye that stains proteins, peptides and amino acids M6 DV measurement: obtain time taken when there is no more change in, results / chromatogram / spots M7 Coherent description of a complete method (M1 to M5) that can be repeated by anyone reading it Reliability and Control: 2 marks any two: R1 Reliability – Obtain replicates / repeats R2 Reliability – Use a t-test to check if there is an significant difference in the data obtained R3 Control – Describe a control by performing the same procedure but by replacing the enzymes with equal volume of distilled water R4 Repeat the whole experiment using a narrower time intervals to more accurately determine the time taken for complete hydrolysis of the protein by each enzyme Data Recording and Manipulation: 1 mark any one D1 Recording – Draw a table showing relationship between independent variable and raw data with appropriate column heading and units + calculate the rate of complete hydrolysis D2 Data manipulation – plot bar graph showing type of protease ( x-axis) and rate of protein hydrolysis (y-axis) (i) State and explain whether each of these conclusions is supported or not supported by all of the information provided about these two enzymes, including the evidence in Fig. 1.2. [3]

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 4 conclusion 1: not supported, because different number of bonds are cut so cannot compare the enzymes conclusion 2: not supported, because some products will be dipeptides conclusion 3: supported, because the endoprotease gives the exoprotease more ‘ends’ to work on OR not supported, because there will be, more / different, dipeptides since endoprotease created new ‘ends’ [Total: 30]

HWA CHONG INSTITUTION / 2022-2023 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 5 QUESTION 2 (a)(i) State which objective lens you have decided to use and give a reason for your choice. [1] 1 low-power, more representative sample 2 high-power, more accurate count (ii) Using the objective lens selected in (a)(i), calculate the mean number of stomata per field of view for L. Show your working. [2] 1 at least 3 counts in whole numbers 2 correct calculation of mean (iii) Focus the objective lens selected in (a)(i) on the stage micrometer provided. The stage micrometer is 10 mm long and has 100 divisions. Calculate the area of the field of view and record this area in mm2. Show your working. [3] 1 calculate length of one stage micrometer division 2 calculate radius of field of view in mm 3 correct calculation of area of field of view in mm2 (iv) Using your results from (a)(ii) and (a)(iii), calculate the mean stomatal density per mm2 for L. [1] correct calculation of mean stomatal density in mm-2 (b)(i) Deduce a relationship between light intensity and stomatal density based on the results shown in Table 2.1. [1] any valid relationship derived from results shown in Table 2.1 (ii)Using an appropriate pair of stomatal densities, justify your answer in (b)(i). [2] any valid pair of stomatal densities calculated from results shown in Ta