ACSI P3 MS - Y4 Exp Bio Prelim 2024

2024 YEAR 4 EXPRESS BIOLOGY PRELIMINARY EXAMINATION Paper 3: Practical (40 marks) 1 (a)(i) 25.00 [1] (ii) • Required columns for table: (percentage) concentration of celery extract, time taken for the paper disc to reach the surface /s for two repeats /trials, mean time taken /s • Correctly labelled headings and units for the columns that are present, • Records the mean results to the nearest whole number • Expected trend: t ime taken for the paper disc to reach the surface is shortest for the highest concentration of celery extract ( 100%) and increases as the concentration of celery extract decreases. [4] (b)(i) Both correct for 1 mark independent variable: (percentage) concentration of catalase /celery extract dependent variable: time taken for the paper disc to reach the surface of H2O2 [1] (ii) The higher the concentration of celery extract /catalase, the quicker the paper disc rises to the surface (Explanation: Hydrogen peroxide is broken down to oxygen and water quicker/ more enzyme- substrate complexes formed and hence oxygen production is faster.) [1] (iii) 2 marks for control + correct explanation Control Explanation Use same volume of distilled water to replace celery extract OR Use boiled celery extract instead This is to show that results are due to the presence of enzymes (catalase) in celery , which is necessary to catalyse the reaction /to produce oxygen that causes the paper disc to reach the surface of the hydrogen peroxide solution. Use same volume of distilled water instead of hydrogen peroxide solution Enzymes (catalase) are specific in action. Hydrogen peroxide is the specific substrate that can fit into the active site of catalase molecules to be broken down / catalysed by catalase. If distilled water is used, the paper discs will not float to the surface. [2] (c)(i) measure the height /distance of the hydrogen peroxide; divided by time taken [2]

(ii) 1 mark for one source of error + effect on results Source of Error Effect on results The reaction began immediately after hydrogen peroxide was poured into the test tube but the stopwatch was only started after the marked level was reached. The time recorded for the paper disc to reach the surface of hydrogen peroxide solution will be less than expected. Difficult to ascertain/ judge when the paper disc reaches the top of the solution The time recorded for the paper disc to reach the surface of hydrogen peroxide solution will be shorter or longer than expected. Paper discs stick to the test tube /not floating up to the surface Accept any other plausible SOE + effect Reject: lack of repeats as a source of error as there were two trials done for each concentration of catalase (d) Any 5 of the below • Independent variable: indicate at least five different sodium chloride conce