A 5-µm cube: SA/V = (6(5)2 )/((5)3 ) = 1.2:1; Elongated cell: SA/V = (2[(2)(5) + (2)(12.5) + (5)(12.5)])/((2)(5)(12.5)) = 1.56:1; therefore Elongated cell has the higher SA:V ratio than 5-µm cube.
B 5-µm cube: V/SA = ((5)3 )/(6(5)2 ) = ≈ 0.83:1; Elongated cell: V/SA = ((2)(5)(12.5))/(2[(2)(5) + (2)(12.5) + (5)(12.5)]) = ≈ 0.64:1; therefore 5-µm cube has the higher V:SA ratio than Elongated cell.
C 5-µm cube: SA = 6(5)2 = 150 square µm; Elongated cell: SA = 2[(2)(5) + (2)(12.5) + (5)(12.5)] = 195 square µm; therefore this compares surface area alone, not surface area divided by volume.
D 5-µm cube: V = (5)3 = 125 cubic µm; Elongated cell: V = (2)(5)(12.5) = 125 cubic µm; therefore this compares volume alone, not membrane area per volume.
