Question

what does a surface area/volume ratio of 3.1 mean for a cell's ability to get materials across the cell membrane compared to the cell with the ratio of 6.1

Answer 1

Each internal region of the cell has to be served by part of the cell surface. As a cell grows bigger, its internal volume enlarges and the cell membrane expands. Unfortunately, the volume increases more rapidly than does the surface area, and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases.