May/June 2026 Paper 13

2026 · 40 questions · 40 parts · 40 marks

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19Diffusion Osmosis Membrane TransportHard1 mark

Macrophages and epithelial cells (squamous, cuboid and columnar) are found in the gas exchange system. The approximate dimensions of these cells are shown.

Diagram (not to scale) comparing four cell shapes, each with its dimensions given above it: W, a macrophage, an irregular round blob of radius 10 $\mu$m; X, a squamous epithelial cell, a thin flattened oval 60 $\mu$m x 60 $\mu$m x 5 $\mu$m; Y, a cuboid epithelial cell, roughly cube-shaped, 21 $\mu$m x 21 $\mu$m x 21 $\mu$m; Z, a columnar epithelial cell, a tall narrow column, 40 $\mu$m x 21 $\mu$m x 21 $\mu$m; each cell contains an oval nucleus.

The surface area to volume ratio for cell W is 0.30 : 1.0 and for cell X is 0.47 : 1.0. Which cells have the most similar surface area to volume ratios?