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. us