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Date May 2019 Marks available 1 Reference code 19M.1.SL.TZ1.1
Level Standard level Paper Paper 1 Time zone Time zone 1
Command term Identify Question number 1 Adapted from N/A

Question

Which graph represents the change in cell surface area to volume ratio with increasing cell diameter?

[Source: © International Baccalaureate Organization 2019]

Markscheme

B

Examiners report

Contrary to the trend of the first question being easy, this proved to be the most difficult in the paper with fewer than 30 % of candidates answering it correctly. Most missed that the graph showed the ratio of surface area to volume, not simply surface area, or perhaps they did not understand that this ratio gets smaller as cell size increases, choosing instead answers showing it getting larger. A and B both showed the ratio getting smaller, but A could be rejected because the line intercepted both x- and y-axes, which isn’t possible if we assume the origin of the axes is zero. A more time-consuming method of identifying B as the correct answer was to do a few sample calculations with cubes of different diameter. For example, the surface area/volume ratios of cubes of diameter 1, 2 and 3 are 6, 3 and 2 respectively, so equal increases in diameter give decreasing decreases in ratio. The line on the graph is therefore curved as in B. Given the significant consequences to living organisms of surface area to volume ratios, this is an area of the programme that deserves more emphasis, if it has previously been neglected.

Syllabus sections

Core » Topic 1: Cell biology » 1.1 Introduction to cells
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