2022 SASS Bio Prelims P3 Ans

Prelim Examination 2022/4Exp ANSWERS Paper 3 – Section A General comments • Ensure you read the whole paper before starting to answer questions. • Consider the wording carefully to gain a full understanding of the specific details required in each section of the response. • Surface area to volume ratio calculations, and then using these to plot a graph, proved difficult. Answer Marks Marker’s Report 1a 200s 1 A wide range of times was provided, and most were accepted. b dimensions of agar cube / mm surface area / mm2 surface area / mm3 surface area:volume ratio distance from surface to the centre of agar cube / mm 2x2x2 24 8 3.00 1 4x4x4 96 64 1.50 2 6x6x6 216 216 1.00 3 8x8x8 384 512 0.75 4 10x10x10 600 1000 0.60 5 3 Many candidates failed to read the instructions to “calculate”, and hence recorded the surface area:volume ratios in formats that were not suitable for use when plotting a graph. Candidates who performed well had clear, accurate calculations, recording data that was suitable for plotting the graph in (d), and standardized to a consistent number of decimal places. Those who performed less well used the format 3:1, 3:2, 3:3, 3:4, 3:5. They also did not simplify the ratios to their lowest values. c 2 Mostly well answered, as both ratio format and calculated

Prelim Examination 2022/4Exp ANSWERS surface area:volume ratio (either column) time taken for whole cube to change colour / s 3:1 3.00 40 3:2 1.50 94 1:1 1.00 203 3:4 0.75 338 3:5 0.60 455 formats were accepted. Candidates were also not penalized for inconsistent decimal places (for the first column) to avoid double penalty. Recording of time taken should be to a consistent number of decimal places. Whole numbers, 1 dp or 2 dp were accepted as the question did not specify the degree of accuracy. d - Axes: Correct plot of surface area/volume ratio value as x-axis and time taken as y-axis - Scale: Proper scale where graph takes more more than half of space given - Plot: values are plotted accurately - Line: smooth curve more appropriate 2 Many good graphs were seen, showing an understanding of the need to have a linear scale and an understanding of the construction of a linear scale, drawing a smooth curve and the use of the x-axis for the independent variable and the y- axis for the dependent variable. Weaker students still confused the axes. Some still extrapolated the lines. A line of best fit was requested. Many drew a straight line when a smooth curve would have been more appropriate. There should be a “0” recorded at the intersection between x- and y- axes. e As surface area to volu me ratio increases, the time taken for the whole cube to change colour decreases (at a decreasing rate). 1 Values must be quoted when describing the trend. Some answers showed confusion about rate of change.

Prelim Examination