Final answer:
Cells are less efficient when large due to a decreased surface area-to-volume ratio, which hinders the diffusion of materials necessary for cell survival.
Step-by-step explanation:
Cells are not efficient when they grow large because of their surface area-to-volume ratio. Surface area is the amount of external space covering the cell, while volume is the internal capacity of the cell. As cells increase in size, their volume grows faster than their surface area due to volume increasing as the cube of the radius, and surface area increasing as the square of the radius. This disproportionate growth means that when a cell becomes too large, it cannot efficiently transfer materials such as nutrients and wastes through its surface. The necessities of life, like oxygen and nutrients, cannot diffuse fast enough through the relatively small surface area compared to the large volume. Thus, large cells struggle with receiving enough materials and getting rid of wastes quickly, which limits their size and leads to less efficient functioning.