1. what happens to the ratio of surface area to volume as the cell size increases without the cell changing shape?

As the cell size increases, the ratio of surface area to volume DECREASES.
The surface area to volume ratio refers to the area per unit volume of a cell. As a cell increase in size, the surface area  and the volume of the cell also increase but at an unequal rate, a point will be reached where the ratio of the surface area to volume will be so low that the diffusion becomes very inefficient, at this point, the cell has to divide in order to increase its surface area to volume ratio and to increase its diffusion rate.