Why are cells spherical instead of cubical if a cube has a larger surface area to volume ratio than a sphere does?
The cells of the body have different sizes, shapes and surface
area to volume ratios depending on their function, that is, their
structure/function relationships. For example, lung alveolar cells
are flat or squamous cells that optimize surface area to volume
ratio for gas exchange between blood and the atmosphere; neurons
have long tubular axons that increase surface area/volume ratio;
cuboidal skin cells of the basal layer are cube shaped and
optimally shaped for blood gas and nutrient exchange as well as for
their function of adherence and skin replicative function; kidney
proximal convoluted tubule cells are cuboid, but extend their
membrane surface area for maximal reuptake of blood nutrients by
the extension of microvilli on the luminal side of the proximal
convoluted tuble. Red blood cells are biconcave discs that,
thereby, increase surface area for gas exchange. White blood cells
are pretty spherical indicating a requirement for maximizing
volume, at the expense of surface area, for antibody production or
bacterial destruction etc. . Skeletal muscle cells are long and
spindle shaped and often fuse together with other muscle cells in
development in order to span the distance across a joint, for
example. But you are correct in stating that a cube would have
greater surface area to volume ratio than a sphere as a function of
length of side or radius (in the case of a sphere).