Cell Theory

Why Cells Are Small

Cells are the basic structural and functional units of life. As life on earth has evolved into organisms of varying complexities, two basic laws of nature have dictated why cells have remained so small. Shorter is faster. This is true both in terms of diffusion and in terms of chemical and electrical movement. By minimizing the distance between a cells nucleus and the numerous proteins and organelles that it must constantly regulate, a cell is maximizing the speed in which intercellular communications can take place while providing the ideal conditions for diffusion: a vital function in the life of a cell. Like wise, the surface area and volume of a cell are directly influential in the efficiency of the cells nutrient absorption and waste expulsion processes. Since the cell membrane of a eukaryotic cell is its only source of nutrition, its surface area must be large enough to allow the cells organelles to receive the materials it needs. This is done by maximizing the surface area to volume ratio. By using the surface area and volume equations for a sphere (4â„-r2 and 4/3â„-r3) you can estimate the surface area of a small cell (5 µm) to be nearly 1,200,000: 1. By modeling the growth rate of the surface area and volume of a sphere on a linear graph its easily discernible that as the size of the sphere increases the ratio of surface area to volume dramatically decreases until finally the volume of the sphere surpasses the surf ace area. Simply, by minimizing its size, a cell is maximizing the speed at which it can communicate the rate at which diffusion can occur, and the amount of surface area at its disposal.

...