2022 HCI JC2 H2 Biology Prelims Paper 4 MS

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2022 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATION PAPER 4 MARK SCHEME Question 1 (a) (i) State your observations of the sides of the test-tube. [1] Ref. to white clumps / precipitate / solid (particles / substance) observed on the inner side of the test tube due to coagulation of milk ; (a) (ii) State how your observations from addition of E differ from your answer in (a)(i). [1] Less / smaller white clumps formed in E compared to H (a) (iii) Based on your observations in (ii), state whether H or E is more effective as a milk coagulant. [1] H; (a) (iv) Confidence in the results of this investigation may be limited by lack of replication and sources of error. Describe two other significant sources of error in this procedure. [2]  Ref. to subjectivity of determining first appearance of white precipitate ;  Ref. to differences in rotating speed / number of rounds of rotation not standardised ;  Ref. to not standardising the speed/ rate at which the plunger of the syringe is released to expel the solution into the test tube ;  Temperature may not have been at the optimum temperature for rennin ;  AVP; (a) (v) Suggest how you could make two improvements to the procedure so that a more accurate estimate of the relative effectiveness on coagulation could be obtained. [2] Any 2:  Filter the coagulant and weigh the mass of coagulant after dying in oven overnight / decant to observe precipitate more clearly ;  Use more milk so that there is more fat and protein to coagulate into a more visible clot ;  Carry out experiment at optimum temperature of rennin using thermometer and thermostatically controlled water bath ;  Use of mechanical rotator / mixer / magnetic stirrer ;  Use of stopwatch to standardise duration of pressing syringe ;  AVP ;

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 2 (b)(i) Use the information provided to plan a method that you can use to determine if PE coagulates milk by its acidity or by the presence of coagulating enzymes such as rennin. Do not plan to carry out repeats. You will carry out this method in step 9. [5]  Describes a method to manipulate independent variable (IV); e.g. prepare two samples of PE, each 2cm3, but one has been boiled for 5 mins and allow to cool for 10 mins, i.e. with (unboiled) and without enzyme (boiled)  Describes a method to determine dependent variable (DV); e.g. using a stopwatch, observe and record the time taken for coagulation to occur for up to 120 seconds  Ref. to at least 2 suitable method used to control the control variables; e.g. use a 5cm3 syringe to add 5 cm3 of M into a clean test tube e.g. setting up a boiling water bath, and use of thermometer to ensure that it is boiling ;  Determines whether coagulation is by enzyme and not acid; e.g. compare the time taken for first appearance of coagulation for the tube containing PE, and, boiled and cooled PE  Ref to risk assessment and safety precaution ; e.g. Wear thermal gloves / safety goggles when taking test tube s in/out of boiling water bath to prevent scalding/burning of hands/ eyes by boiling water ; (b)(ii) Use the space provided to record your results in a suitable format. [3] coagulant / solution that was added to milk time taken for coagulation to occur / s (unboiled) PE 30 Boiled and cooled PE 90 (A: >120)  Correct column headings with units; IV: coagulant / solution added to milk DV: time taken for coagulation / first appearance of white precipitate (in seconds)  Time taken recorded to whole number of seconds ;  Correct trend (increased time taken for boiled and cooled PE) ;

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 3 (b)(iii) Based on your results, state and explain whether the coagulative properties of pineapple is due to acidity, enzymes or both. Give a reason for your answer. [4]  Both acid and enzymes;  In boiled and cooled PE, enzymes were denatured (ref. to loss of 3D conf of active site)  However, coagulation still occurs due to acid present in PE ;  Accurate quoting of student’s data ; OR  Only enzymes (if no coagulation is observed >120s)  In boiled and cooled PE, enzymes were denatured (ref. to loss of 3D conf of active site)  Coagulation no longer occurs because no acid;  Accurate quoting of student’s data ; (b)(iv) State an assumption that needs to be made in order for your conclusion to be valid. [1]  The enzyme rennin must denature when boiled and cooled at 100 degrees celsius for 10 minutes ; [Total: 20] QUESTION 2 (a) (i) State and explain a hypothesis that could be used to predict the results of testing these two samples. [2]  The test-tube with the type of sugar substrate, that is more easily broken down / hydrolyse d by starter culture / yeast and bacteria ;  will have darker pink colouration when TTC is added, and has a higher rate of respiration ; (a) (ii) Record your results in the space below. [2] Type of sugar Intensity of colour C1 3 / 4 C2 0 1. Correct column headings (no units); IV: type of sugar (C1, C2) DV: intensity of colour 2. Correct trend, C1 > C2 ; (a) (iii) Identify and explain whether C1 or C2 is more likely to be maltose. [2]

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 4  C1;  Higher intensity of colour observed as maltose is a disaccharide, and has two glucose per molecule / twice the amount of glucose ; OR  C2;  Higher intensity of colour observed as yeast and bacteria contain enzymes for breaking down glucose but not maltose ; (b) (i) Use the grid provided to display the results in Table 2.2. [4]  Correct axis labels + correct units ; x-axis: type of sugar y-axis: rate of respiration / a.u.  Graph occupying at 50% on the area of the total grid + no odd scales ;  Bars are plotted accurately to half of a smallest square + bars of replicates for each culture side- by-side + gap present between two different starter cultures ;  Appropriate legend to differentiate bars for R1 and R2 ; (b) (ii) State what the standard deviation shows about the results of this investigation. [1] s shows the spread of data about the mean, the smaller the s value implies that the sample mean is more likely a representative of the true mean / results are more reliable ;

HWA CHONG INSTITUTION / 2021-2022 H2 BIOLOGY / Preliminary Examination Paper 4 / MS 5 (b) (iii) Calculate the value of t and the number of degrees of freedom, using these formulae. [2]  t = 10.8 (3.s.f) + working shown ;  v = 15 + 15 – 2 = 28 ; (b) (iv) The critical value of t at the 5% level of significance is 2.05. Explain whether the results of this t -test can help the student determine which starter culture is better for cheese making. [2]  t calculated value of 10.8, is greater than the t critical value of 2.05 at a 5 % level of significance ;  there is less than 5% possibility that the difference in the rates of respiration occurs due to chance, the starter culture Y is significantly more effective than starter culture B at cheese making ; [Total: 15