HCI 2024 Prelim H2 Bio P4 Ans

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2024 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 4 MARK SCHEME QUESTION 1 (a)(i) State the independent variable in this investigation. [1] number of beads (ii) Record your results in an appropriate table. [4] number of beads time taken for appearance of the first colour change / s 1 more than 120 2 more than 120 4 42 8 20 16 13 1 correct column headings and units 2 times recorded for five sets of beads 3 all times recorded in seconds 4 correct trend (iii) Explain your results in (a)(ii). [2] 1 ref. to more active sites available 2 ref. to more reducing sugar produced (iv) Other than lack of replicates and repeats , identify one main source of error in this investigation and suggest an improvement to reduce the effect of this error. [2] Source of error Improvement S1 ref. to beads having different sizes I1 ref. to use of different concentration of yeast enzymes S2 ref. to beads not left for the same duration in sucrose I2 ref. to staggering start times S3 ref. to sodium alginate and yeast may not be mixed well manually I3 ref. to use of magnetic stirrer (a)(v) A student set up a beaker as a control experiment. The result of the control experiment showed that the sucrose was hydrolysed by an enzyme. Suggest what substances the student put in the beaker for the control experiment. [1] boiled and cooled yeast

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 2 (a)(vi) The procedure described in step 1 to step 20 investigated the effect of changing the number of yeast beads on the rate of hydrolysis of sucrose. Describe how you would modify the procedure to investigate the effect of changing the concentration of the sucrose solution on the rate of hydrolysis of sucrose. [2] 1 use a set number of yeast beads 2 prepare at least five concentrations of sucrose by dilution (b)(i) Record the colour change of TTC after 10 minutes. [1] colourless to pink (b)(ii) Explain why the colour change of TTC in (b)(i) can only be observed after 10 minutes and not immediately upon addition. [2] 1 ref. to hydrolysis sucrose into reducing sugars 2 ref. to reduction of TTC due to respiration (c) Describe a method that students could use to compare the respiration rates of the three varieties of yeast. [7] 1 same / stated / known, volume (suspension), of each yeast (added to separate flasks) 2 same / stated / known, volume of, nutrient solution / sucrose 3 ref. to method to maintain temperature 4 suitable temperature in range 15 °C – 80 °C 5 idea