How does surface area to volume ratio affect the rate of diffusion?

Simply put, surface area to volume ratio refers to the size of the surface area relative to the volume of substance that can pass through it at a given time. Since humans have a small surface area to volume ratio and a flat body, diffusion occurs very slowly or not at all, whereas amoeba and certain bacteria have large surface area to volume ratios and high diffusion rates.

Because volume is cubed where surface area is squared, when a cell gets bigger, its volume grows more quickly than its surface area.

Diffusion is less efficient and takes longer when the surface area is smaller than the volume. This is because the substance that is being diffused needs to cover a larger area, but there is less area available for the substance to actually enter the cell.

This is the actual reason for cell division: cells lose efficiency and split in half to increase the surface area to volume ratio when they grow too big and take too long to move materials across the cell.

The surface area to volume ratio influences the rate of diffusion because as the ratio rises, more surface area becomes available for molecules to diffuse across in relation to the volume they must pass through. This leads to a faster rate of diffusion because molecules have to travel less distance to reach the interior of the object from the surface.