Why are cells so small
A pint of human blood contains more than five billion cells and we lose more than seven hundred billion cells as dead cells each day unconsciously; these statistics should give one an idea about exactly how small each cell in our body is. Cells form, divide, repair, grow, function and die every day throughout our body, but neither do we see the changes nor do we generally feel any of the processes and that is because they are too small. If cells were much bigger than what they are, then each time specific cells died out in a particular area of our body, it would be visible or felt due to lack of sufficient active cells to take over functionality. Since the cells would be larger, therefore the re-growth of the cells would also be slower as well thus the particular organ would not be able to function properly in the meanwhile. Thus the continuous chain of cellular processes would no longer go on without affecting the organism as a whole. It is therefore a necessity for our cells to remain microscopic in order for us to function and survive.
Another point to be noted while considering cell size is the fact that cells must stop growing at one point just to survive. The problem lies in the fact that the ratio of the surface area of a cell to its volume reduces as the cell grows because the volume of a cell has a much accelerated growth rate than its surface. The basic function of a cell is to absorb the necessary materials from food and water while passing the waste material out of it. The two-way process is carried out through the surface of the cell and so it must stop growing seeing that otherwise the surface area would soon become too small in comparison to the volume to carry out the basic function of absorption and excretion. Any cell that grows beyond what it should ceases to function and dies eventually because of this phenomenon.