If the diameter is 10 times as big, the radius must also be 10 times as big since 2r = d. Now, if we have 2 cells, one with radius = r, and the other with radius = 10r and the equation for volume = 4/3pi(r)^3, the second cell will be 1000 times as big because r is cubed. Sorry was in a rush, hope that made sense!