Cells must exchange different mole cules across their boundaries in order to survive. The amount of material that can be taken in or released is limited by the surface area of the cell. a If the ratio of surface area to volume is too low, then the cell is unable to exchange enough material. i Find, in terms of its radius r, the ratio of surface area to volume of a spherical cell. ii Find the largest possible radius of the cell, in metres, if the ratio of surface area to volume must be greater than 955000 (with the radius measured in metres). b Find an expression in terms of radius r for the ratio of surface area to volume for each of the following objects, given that their volume is equal to that of the sphere of radius r: i A cube. ii A cylinder with two halfspheres attached at its bases, and height of cylinder equal to ve times the radius of its base. iii Hence, if the sphere has unit volume, nd how many times more surface area each object will have than the sphere.