Answer: the answer is the surface area
Explanation: The increase in the radius of the cell will cause an increase in the area of the cell.
The larger the area of the cells, the faster will be the rate of diffusion. The rate at which materials are exchanged will be increased.
The increase in the cell size, however, causes a decrease in the area-to-volume ratio, which will result in efficient diffusion.
Thus, the surface area of the cell and its volume play a crucial role in the exchange of material with the surrounding.