When the cell enlarges beyond its capacity, it fails to supply enough material that can cross the membrane sooner so as to occupy the cellular volume. Hence the diffusion rate also decreases so as the ratio. The cell carry out its various functions to sustain through diffusion when diffusion rate is low it will ultimately affect the ratio. Bigger size affects the diffusion of the material to the out of the cell. as we know the diffusion occurs across the surface of the cell.
