Question

What single factor limits the size that most cells are able to attain?

Answer 1

Maintaining a favorable surface-area-to-volume ratio.

Explanation:

Having a high surface-area-to-volume ratio in a cell results in great efficiency within a cell (greater rate of exocytosis, endocytosis, metabolism).

Without this high ratio, a cell will be largely inefficient and not be able to do its job properly. Thus, cells are generally small because if they become too big they will lose that high surface-area-to-volume ratio.