It sounds like the cell is very long and thin, which would lead to a greater surface area-to-volume ratio than for the middle cube in Fig. 6.7 but not as much as the short-and-thin cube at the left end of Fig. 6.7. The cell in question would have 502 square units of area and 125 cubic units of volume, and a ratio of ~4 units, which agrees with the prediction (see Fig. 6.7).
Work Step by Step
The cell in question would have 125 square units of area for each of the four long sides (draw a cube and see that each of these sides is 125 units long and 1 unit tall) and 2 square units for both of the two ends, each one being unit tall and one unit long, for 502 square units total. The volume is 125x1x1 cubic units=125 cubic units. Divide the surface area by the volume to get the ratio (502\125=4.016), and compare with Fig. 6.7.