surface area/volume ratio
surface area/volume ratiothe important relationship between the surface area of a biological unit such as a cell or a whole animal, and its overall volume, which affects many aspects of its biochemistry. As the size of the unit increases, its surface area grows relatively more slowly than its volume. For instance, a perfect cube would increase its surface area as the square of the original size, while the volume would increase as the cube of the original size. Thus a cube with sides of 1 cm has a surface area of 6 cm2 and a volume of 1 cm3; trebling the dimensions of the cube produces a surface area of 54 cm2 (a ninefold - 32 - increase) and a volume of 27 cm3 (a 27-fold - 33 - increase). This relationship may explain why, for example, cells are small, with a large SA:vol. ratio giving a relatively large cell-membrane surface for the transport of molecules and to allow heat loss. See BERGMANN'S RULE.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005