Final answer:
Cell size is primarily limited by the surface to volume ratio. This ratio determines how effectively a cell can transport materials across its plasma membrane in relation to its volume.
Step-by-step explanation:
Cell size is limited by surface to volume ratios. As a cell increases in size, the surface area-to-volume ratio decreases. This means that if the cell grows too large, the plasma membrane will not have a sufficient surface area to support the rate of diffusion needed for the increased volume. Larger eukaryotic cells have developed structural adaptations to enhance cellular transport and overcome this limitation. If these adaptations were not in place, the increased difficulty in acquiring sufficient materials to support cellular processes would limit the cell size significantly.