and if you do convert your nurb sphere (or just create a new poly sphere), you apply the transparency this way:
1) Choose Window>Rendering Editor>Hypershade.
2) In Hypershade choose Create>Material>(whatever material you want)
3) A lambert material appears in Hypershade. Double-click it, then change the transparency value to your liking.
4) Close the window for the material.
5) Display faces on your object, select the face you want to be transparent, then right-click the lambert swatch in Hypershade and choose "assign material to selection."