Answer:Cells are small because they are more efficient as smaller entities. Information within small cells is transmitted more quickly and efficiently than within larger cells. The nucleus or "command center" of the cell initiates cellular activity by converting genetic information into functional molecules, such as proteins. These proteins and other molecules are then directed around the cell to perform specific functions. The larger the cell, the longer these proteins and other cellular processes will take to carry out their functions. This is quite energy expensive and a less than ideal situation; therefore, cells tend to be relatively small.
As cells increase in size, the volume increases by a power of 3, whereas the surface area increases by a power of 2. This expansion results in a lower surface area-to-volume ratio that is less efficient for transmitting information through cells. Information coming into, traveling through or exiting cells must traverse a much greater distance (through the increased volume) to reach its final destination. Thus a higher cell surface area-to-volume ratio, i.e., smaller cell size, is desired for most efficient cellular activity. Additionally, and importantly, the smaller surface area and larger volume of larger cells does not permit enough molecules to pass in or out of the cell. Because information can enter or exit a cell through it's plasma membrane, the greater the surface area-to-volume ratio, the more molecules that can enter or exit per unit of volume. This is also much more efficient for cells.
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